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Master

Affiliation (Master)

  • Faculty of Engineering　Mechanical and Aerospace Engineering　Thermal and Fluid Systems

Affiliation (Master)

  • Faculty of Engineering　Mechanical and Aerospace Engineering　Thermal and Fluid Systems

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Profile and Settings

Degree

  • PhD.（1996/07 The University of Tokyo）

Profile and Settings

  • Profile

    Laboratory for Flow Control (LFC) deals with experimental research on various energy and environmental problems issued in the field of mechanical engineering. We develop ship drag reduction technology, food engineering device, 3D-driven wind turbine, geo-thermofluid physics, and fuel flowmetering management. Particle image velocimetry (PIV) and ultrasound velocity profiling (UVP) support new discoverty of fluid mechanics and assist new design of fluid machinaries.

  • Name (Japanese)

    MURAI

  • Name (Kana)

    Yuichi

  • Name

    200901065173477867

Alternate Names

Achievement

Research Interests

  • Flow Measurement   Natural Energy   Wind turbine   Bubble   Drag Reduction   Ship   Visualization   PIV   Ultrasound   Microbubble   Fluid Engineering   Wind Engineering   Multiphase Flow   Bird   Energy   画像計測   流体力学   Image analysis   Fluid Dynamics   

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Disaster prevention engineering
  • Aerospace, marine, and maritime Engineering / Marine and maritime engineering
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Measurement engineering
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Fluid engineering

Research Experience

  • 2010/04 - Today Faculty of Engineering, Hokkaido University Professor
  • 2005/04 - 2010/03 Graduate School of Engineerig, HokkaidoUniversity Associate Professor
  • 2003/04 - 2005/03 Graduate School of Engneering, Hokkaido University Associate Professor
  • 2001/03 - 2003/03 Imperial College London Visiting Researcher
  • 2000/06 - 2001/02 Faculty of Engineering, Fukui University Associate Professor
  • 1995/04 - 2000/05 Faculty of Engineering, Fukui University Research Associate
  • 1993/04 - 1995/03 Graduated School of Engineering, The University of Tokyo JSPS Research Fellow

Education

  •        - 1996/07  PhD
  •        - 1995/03  The University of Tokyo  Graduate School of Engineering  PhD Course ( Withdrawal)
  •        - 1995/03  The University of Tokyo  Graduate School of Engineering  Division of Mechanical Engineering
  •        - 1991/03  Kanazawa University  Faculty of Engineering
  •        - 1989/03  Ishikawa National College of Technology  Department of Mechanical Engineering

Committee Memberships

  • 2023/08 - Today   JSMF   President
  • 2022/09 - Today   Science Council of Japan   Associate Member
  • 2022/04 - Today   JSME   Board Member, Fellow member
  • 2022/01 - Today   JSFM   Fellow
  • 2020/07 - Today   JST   CRDS advisory committee member
  • 2020/07 - Today   PIV International Symposium   Scientific Committee
  • 2020/06 - Today   Int Symp Doppler Method   Board Member
  • 2018/07 - Today   Lisbon International Laser Conference   Board member
  • 2018/01 - Today   Experiments in Fluids   Associate Editor
  • 2016/04 - Today   JSME Research Committee Chair
  • 2022/08 -2023/08   VSJ   Chair of VSJ Symposium
  • 2016/06 -2023/04   ICMF Governing Board Chair
  • 2019/08 -2022/07   JSMF   Board Member : Int Affair Chair, Vice Chair of JSMF
  • 2021/04 -2022/03   JSME   Representative Member
  • 2016/01 -2021/01   Nuclear Eng. Design   Editor
  • 2012/10 -2017/12   Advisory Editorial board

Awards

  • 2023/03 JSME Hokkaido Branch Technical Award
     国際マラソン用に対応した開口型ロードコーンの耐風技術の開発 
    受賞者: 村井祐一;田坂裕司;朴 炫珍;芦田俊樹;永井繁行
  • 2022/08 JSMF Contribution award
     「学会の国際交流への貢献」 
    受賞者: Yuichi Murai
  • 2020/08 Japan Society of Multiphase Flow Paper Award
     Bubble clustering in gas-liquid two-phase turbulent flow 
    受賞者: Y.Oishi;Y.Tasaka;Y.Murai
  • 2020/07 Visualization Society of Japan VSJ Award
     「回転レーリーベナール対流の渦温度場可視化」 
    受賞者: D.Noto;Y.Tasaka;T.Yanagisawa;H.J.Park;Y.Murai
  • 2018/07 Visualization Soc Japan Technology Award
     Ultrasonic food rheometry 
    受賞者: T.Yoshida;Y.Tasaka;H.J.Park;Y.Murai
  • 2017/04 JSME Technology Award
     「二相流境界層のスマート制御」 
    受賞者: Y.Murai;I.Kumagai;Y.Tasaka;H.J.Park;Y.Takahashi
  • 2017/02 IOP Outstanding Reviewer's Award
     
    受賞者: Yuichi MURAI
  • 2016/03 JSME Branch Award
     Wind farm birdstrike prevention 
    受賞者: Y.Murai;Y.Tasaka;Y.Oishi;Y.Takeda;H.Kumeno
  • 2015/06 Visualization Soc Japan Technical Award
     「文学の流体力学的可視化」 
    受賞者: M.Yamada;Y.Murai;I.Kumagai
  • 2014/07 Japan Society of Multiphase Flow Technical Award
     「混相流の超音波計測」 
    受賞者: Y.Murai;Y.Tasaka;Y.Takeda
  • 2014/07 Visualization Society of Japan Techncal Paper Award
     「粘弾性流体の可視化」 
    受賞者: T.Shiratori;Y.Tasaka;Y.Murai;Y.Takeda
  • 2012/07 JSMF Technical Paper Award
     「水中翼気泡発生装置」 
    受賞者: I.Kumagai;Y.Tasaka;Y.Murai
  • 2011/10 JSME Fluid Eng Div. Frontier Award
     「二相流体工学技術」 
    受賞者: Yuichi MURAI
  • 2010/11 日本ガス協会 Paper Award
     「パイプライン流量計」 
    受賞者: T.Takeuchi;Y.Murai
  • 2010/08 日本混相流学会 日本混相流学会・論文賞
     「気泡流のレイノルズ応力」 
    受賞者: 大石義彦;村井祐一;田坂裕司;武田 靖
  • 2009/07 可視化情報学会 可視化情報学会・最優秀講演賞
     「バードストライク」 
    受賞者: 村井祐一;田坂裕司;武田 靖
  • 2009/07 可視化情報学会 可視化情報学会・20周年記念功労賞
     「混相流OS」 
    受賞者: 村井祐一
  • 2009/03 北海道大学 北海道大学・エクセレントティーチャーズ
     「応用数学」 
    受賞者: 村井 祐一
  • 2008/07 可視化情報学会 可視化情報学会・技術賞
     「宇宙用ギアポンプ」 
    受賞者: 村井祐一;上埜安隆;大岩浩司;宮城直樹;山本富士夫;伊東哲也
  • 2007/10 油空圧機器技術振興財団 油空圧機器技術振興財団・論文賞
     「マイクロポンプ」 
    受賞者: 宮城直樹;村井祐一;宮﨑孝司;山本富士夫
  • 2007/04 MEXT Minister Award
     「流体エネルギー制御システム技術」 
    受賞者: 村井祐一
  • 2005/10 日本機械学会 日本機械学会流体工学部門・貢献賞
     「日韓熱流体会議の運営」 
    受賞者: 村井 祐一
  • 2005/04 日本機械学会 日本機械学会・論文賞
     「気泡間相互作用」 
    受賞者: 北川石英;杉山和靖;笹木俊男;村井祐一
  • 2003/04 日本機械学会 日本機械学会・教育賞
     「市民機械工学講座」 
    受賞者: 村井祐一;伊藤隆基;永井二郎;本田知己;石川拓司
  • 2000/07 日本混相流学会 日本混相流学会・貢献賞
     「ホームページ構築」 
    受賞者: 村井 祐一
  • 1998/07 可視化情報学会 可視化情報学会・研究奨励賞
     「二相流のステレオ可視化」 
    受賞者: 村井 祐一
  • 1998/04 日本機械学会 日本機械学会・論文賞
     「気泡流の数値解析法」 
    受賞者: 松本洋一郎;村井祐一
  • 1989/03 日本機械学会 日本機械学会・畠山賞
     
    受賞者: 村井 祐一

Published Papers

  • Wenqing Zheng, Yuji Tasaka, Kohei Ohie, Yuichi Murai
    Measurement Science and Technology 0957-0233 2024/09/10 
    Abstract We propose a method for estimating volume fraction of emulsions based on ultrasonic velocity profiling viscometry and validate its feasibility through a series of experiments. The experiments involve emulsions composed of silicone oil as continuous phase and tap water with volume fractions ranging from 10vol% to 30vol%. We introduce the viscosity model for this emulsion to establish the mathematical relationship between volume fraction and viscosity. Subsequently, we calibrate this relationship using ultrasonic spinning rheometry (USR). The identified equation is then applied in estimating the inline volume fraction using ultrasonic velocity profiling combined with pressure drop measurement. The key idea is that by measuring the viscosity in a pipeline the volume fraction is then indirectly estimated employing the identified equation. Through the collection and analysis of experimental data, we confirmed that the USR can capture the characteristics of the emulsion viscosity accurately. Moreover, we found that this method demonstrates applicability and accuracy in measuring volume fractions of emulsions. The results indicate that the mean relative error for this estimation is 24.06% at a volume fraction of 10vol%, and 4.78% at a volume fraction of 30vol%.
  • Sotaro Masanobu, Satoru Takano, Marcio Yamamoto, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    Journal of Offshore Mechanics and Arctic Engineering 1 - 40 0892-7219 2024/07/16 
    Abstract The pressure loss due to the hydraulic transport of large solid particles should be predicted for the design of subsea mining systems. The mixture flow in a flexible jumper is expected to be unsteady during lifting operations in an actual mining system. The authors develop a one-dimensional mathematical model that predicts such pressure loss under pulsating mixture flows in a static inclined pipe assuming that the flow in the jumper is fully developed. An experiment is performed on the hydraulic transport of solid particles to obtain data for model validation. In this experiment, several kinds of solid particles are used: alumina beads, glass beads, and gravel. The experimental parameters are mixture velocity, solid concentration, pulsation period and amplitude of water velocity, and pipe inclination angle. The proposed model is validated through a comparison with experimental data. Furthermore, we calculate the pressure loss due to the hydraulic transport of polymetallic sulfide ores using the proposed model. The calculation results show that the time-averaged pressure loss drastically varies with the pipe inclination angle, reaching its maximum value between the pipe inclination angles of 30° and 60°, at which the flow is inclined upward. The results also show that the amplitude of pressure loss pulsation differs little between pipe inclination angles and that the pulsation component of pressure loss should be considered in designing lifting systems.
  • Yuichi MURAI, Shuji OTOMO, Susumu OSUKA, Tetta YAMAGUCHI
    Transactions of the JSME (in Japanese) 90 (933) 2024/05 [Refereed][Not invited]
  • Yasufumi HORIMOTO, Itsuki MORI, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI
    Journal of Fluid Science and Technology 19 (2) JFST0013 - JFST0013 2024/05 [Refereed][Not invited]
  • Yoshimichi Ono, Ryosuke Sayama, Yuichi Murai, Hyun Jin Park, Yuji Tasaka
    Wind Energy 27 483 - 499 1095-4244 2024/04/17 [Refereed][Not invited]
     
    Abstract The use of a turbo‐sail airfoil to improve the power generation of a Darrieus wind turbine was examined. The turbo‐sail airfoil comprises a symmetric blade from which a high‐speed tangential jet is produced to suppress flow separation. For a steady angle of attack, we experimentally confirmed an anti‐stall function of the airfoil at an angle of attack up to and exceeding 30°. Considering the case of the rotation of a single blade of a Darrieus wind turbine, the flow field was replaced with a non‐separated stream around the airfoil particularly even at a tip‐speed ratio lower than 3. The pressure field and local lift‐to‐drag ratio measured by particle image velocimetry quantitatively supported the expected anti‐stall function. Improvements in the torque and power coefficient were estimated from measurements considering the external power consumed in supplying the jet.
  • Yuichi Murai, Takahiro Umemura, Hyun Jin Park, Yasufumi Horimoto, Yuji Tasaka
    Journal of Fluids and Structures 127 104105  2024/04 [Refereed][Not invited]
  • K. Ohie, Y. Tasaka, Y. Murai
    Journal of Fluid Mechanics 983 (A39) 2024/03/25
  • Shūji Ōtomo, Yuji Tasaka, Petr Denissenko, Yuichi Murai
    Physics of Fluids 36 (027104) 1070-6631 2024/02/01 [Refereed][Not invited]
     
    With an increasing demand for small energy generation in urban areas, small-scale Savonius wind turbines are growing their share rapidly. In such an environment, Savonius turbines are exposed to low mean velocity with highly turbulent flows made by complex geographies. Here, we report the flow-induced rotation of a Savonius turbine in a highly turbulent flow (18% turbulence intensity). The high turbulence is realized by using the far-field of an open-jet. Compared to low turbulence inflow (1% turbulence intensity), the turbine rotates 4% faster in high turbulence since the torque/power increases with turbulence intensity. The wake measurement by hot-wire anemometry and particle image velocimetry reveals the suppression of vortex shedding in high turbulence. In addition, a newly developed semi-empirical low-order model, which can include the effect of turbulence intensity and integral length scale, also confirms high turbulence intensity contributes to the rotation of the turbine. These results will boost more installation of small Savonius turbines in urban areas in the future.
  • Yoshihiko Oishi, Sho Onuma, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hideki Kawai
    Flow Measurement and Instrumentation 96 102546 - 102546 0955-5986 2024/02 [Refereed][Not invited]
  • Hyun Jin Park, Tatsuya Hamada, Chiharu Kawakita, Yuichi Murai
    Ocean Engineering 289 116248 - 116248 0029-8018 2023/12
  • Taiji Tanaka, Ryo Aoki, Yuichi Murai
    Experiments in Fluids 64 (147) 0723-4864 2023/08/12 [Refereed][Not invited]
  • Sotaro Masanobu, Satoru Takano, Marcio Yamamoto, Yuichi Murai, Yuji Tasaka, Hyun Jin Park
    Volume 4: Ocean Space Utilization 2023/06/11 [Refereed][Not invited]
     
    Abstract For subsea mining, it is important to predict the pressure loss in oscillating pipes with pulsating slurry flow for the safe and reliable operation of ore lifting. The configuration of pipe is expected to have not only vertical but also inclined parts. In the present paper, the authors focused on the pulsating internal slurry flow in static inclined pipes and derived the mathematical model to predict the pressure loss in such conditions. The slurry transport experiment was carried out to investigate the effects of pulsating slurry flow on the pressure loss in inclined pipes. In the experiment, the data related to slurry flow was measured by the differential pressure gauges, the electromagnetic flowmeter and the ultrasound monitoring. The model derived was validated by a comparison with measured data. The measured pressure loss has an outstanding component with pulsating period of water flow with relatively small higher order harmonic components. Although the prediction model derived in the present study has a tendency to overestimate the pressure loss for larger inclination angles, the calculated pressure loss is within the acceptable range given the simplicity of the model.
  • Hanrui Zhang, Feng Dong, Yuichi Murai, Chao Tan
    Flow Measurement and Instrumentation 90 102326 - 102326 0955-5986 2023/04 [Refereed][Not invited]
  • Daisuke Noto, Yuji Tasaka, Yuichi Murai
    Experiments in Fluids 64 92  2023/04 [Not refereed][Invited]
  • Dongik Yoon, Takumi Hayashi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Satoru Takano, Sotaro Masanobu
    Flow Measurement and Instrumentation 91 102357 - 102357 0955-5986 2023/03 [Refereed][Not invited]
  • Taiji Tanaka, Yoshihiko Oishi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Chiharu Kawakita
    Ocean Engineering 272 113807 - 113807 0029-8018 2023/03 [Refereed][Not invited]
  • Yuichi Murai, Masaaki Ishikawa
    Nuclear Technology 209 1 - 14 0029-5450 2023/02/24 [Refereed][Not invited]
  • Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    Industrial & Engineering Chemistry Research 61 (49) 18157 - 18164 0888-5885 2022/12/14
  • Behaviors of sliding bubbles in an inclinable turbulent channel flow investigated by optoacoustic measurement
    D.Yoon, H.J.Park, Y.Tasaka, Y.Murai
    International Journal of Multiphase Flow, Vol. 158, No. 104258 (2022) 2022/10 [Refereed][Not invited]
  • A.Kitagawa, M.Ota, T.Watamura, T.Tonooka, Y.Murai
    Chemical Engineering Science, Vol. 264, No. 118163 (2022) 264 118163 - 118163 0009-2509 2022/10 [Refereed][Not invited]
  • Yuichi MURAI, Yuji TASAKA, Hyun Jin PARK, Satoru TAKANO, Sotaro MASANOBU
    JAPANESE JOURNAL OF MULTIPHASE FLOW 36 (3) 329 - 335 0914-2843 2022/09/15
  • H.J.Park, D.Yoon, S.Akasaka, Y.Tasaka, Y.Murai
    Experiments in Fluids, Vol. 63, No. 130 (2022.8) 63 (8) 0723-4864 2022/08 [Refereed][Not invited]
  • Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Masako Sugihara-Seki, Yuichi Murai
    Experiments in Fluids 63 (8) 0723-4864 2022/08
  • Yuichi Murai, Takumi Hayashi, Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Satoru Takano, Sotaro Masanobu
    Experiments in Fluids 63 (8) 0723-4864 2022/08
  • Evaluation of time-dependent rheological property in the coagulation of skimmed milk by ultrasonic velocity profiler
    A.Takano, K.Ohie, Y.Horimoto, Y.Tasaka, Y.Murai
    Transaction of JSME, Vol. 88, No. 911, pp.1-13(2022) 2022/07 [Refereed][Not invited]
  • Sotaro Masanobu, Marcio Yamamoto, Satoru Takano, Yuichi Murai
    Proceedings of the ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering (OMAE2022) 4 OMAE2022-79597  2022/06 [Refereed]
     
    Abstract For design and operation of subsea mining system, it is important to predict pressure loss due to the hydraulic transport of solid particles in the flexible jumper which connects the mining tool to the vertical lifting pipe via subsea slurry pump. The configurations of jumper would change according to the motions of the mining tool and the slurry pump, which may be easier to cause the pipe blockage than the vertical pipe. In the present paper, we investigated the effects of jumper configuration on the pressure loss. We assumed the 100 m long flexible jumper of which outer and inner diameters are 0.254 m and 0.200 m, respectively. PMS ore, of which density and diameter are 3,440 kg/m3 and 0.03 m respectively, were assumed as the solid particles. We varied the slurry transport conditions such as slurry concentration and slurry velocity under the condition of a constant production rate of 5,000 t/day. The effects of jumper configuration on internal slurry flow were studied from the viewpoint of pressure loss and specific energy consumption. The allowable slurry velocity in jumper system was also investigated considering pipe inclination by referring to the past literature. Finally, the most desirable operational slurry flow condition was discussed for the jumper system studied.
  • Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    Physics of Fluids 34 (5) 053301 - 053301 1070-6631 2022/05 
    The behavior of bubbles traveling in the proximity of a tilted wall is studied experimentally to understand the fundamental sliding motion of bubbles inside turbulent boundary layers along an inclined wall. The qualitative visualization of sliding bubbles confirms the contribution of bubble buoyancy on the sliding motion for negative and positive inclinations of the channel. An opto-acoustic combined measurement technique is adopted to explore the sliding motion. Liquid velocity profiles in the bubbly flow and the distance between the wall and bottom of the bubble are obtained using the ultrasound pulsed Doppler method, while the bubble diameters and velocities are obtained from particle-tracking type image processing. The combined measurements reveal that the velocity of bubbles decreases under the negative slope condition and increases under the positive slope condition due to opposite buoyancy effects. In addition, the distance between the wall and bottom of the bubble increases with an increase in negative inclination. The lift coefficient is derived from the measured variables using a force–balance equation among the buoyancy, lift, and surface tension. Finally, we propose modeling equations for the lift coefficient expressed in terms of the Reynolds, Weber, and Bond numbers, which apply to the bubbles inside boundary layers.
  • Taiji Tanaka, Yoshihiko Oishi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Chiharu Kawakita
    Ocean Engineering 252 111224 - 111224 0029-8018 2022/05
  • Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    International Journal of Multiphase Flow 149 103995 - 103995 0301-9322 2022/04
  • Taiki Yoshida, Yuji Tasaka, Kohei Ohie, Yuichi Murai
    Nihon Reoroji Gakkaishi 50 (1) 3 - 7 0387-1533 2022/02/15
  • Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    EXPERIMENTS IN FLUIDS 63 (2) 0723-4864 2022/02 
    We propose a practical map representation termed rheology mapping for comprehensively evaluating the dependence of viscoelasticity on applied shear deformation and shear timescale represented by oscillation frequency, utilizing ultrasonic spinning rheometry, which has excellent applicability to a wide variety of polymer solutions. The rheology mapping was applied to two typical kinds of polymer solutions. One is carboxymethyl cellulose (CMC) aqueous solution, a well-known viscous and shear thinning fluid. The other is polyacrylamide (PAM) aqueous solution generally considered as a viscoelastic fluid while its viscoelasticity is difficult to be evaluated by a standard torque-type rheometer. The rheology mapping for the solutions showed notable rheological properties. The viscoelasticity of both the CMC and PAM solutions vary widely from elastic to viscous, depending on the applied shear rate, strain, and oscillation frequency. The mapping also revealed the clear dependence of the viscosity of the solutions: the CMC solutions on the shear rate and the PAM solutions on the shear strain. These results provide quantitative support of findings in other reports associating these macroscopic properties with the microscopic dynamics of polymer coils.[GRAPHICS].
  • Taiki Yoshida, Yuji Tasaka, Peter Fischer, Yuichi Murai
    Applied Clay Science 217 106395 - 106395 0169-1317 2022/02
  • H.J. Park, Y. Tasaka, Y. Murai
    International Journal of Multiphase Flow 2022/01 [Refereed]
  • Taiji TANAKA, Yoshihiko OISHI, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI, Chiharu KAWAKITA
    Transactions of the JSME (in Japanese) 2022
  • Y. Murai, T. Yumoto, H.J. Park, Y. Tasaka
    Experiments in Fluids 62 231  2021/11 [Refereed]
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    Experiments in Fluids 62 (9) 1432-1114 2021/09/01 
    We experimentally investigate air bubbles sticking to a hydrophobic strip on a hydrophilic ceiling in a horizontal turbulent channel flow. Simultaneous measurements of wall-sticking bubbles are conducted in two perpendicular planes using two cameras to estimate their size and contact angles and hence evaluate the drag coefficient. In a range of the bubble Reynolds number, Reb (250 ≤ Reb ≤ 1480) and a range of the Weber number, We (0.7 ≤ We ≤ 6.5), the drag coefficient for a single, deformable bubble stuck on the surface is almost independent of Reb and We and tends to be slightly higher than that of a non-deformable bubble fixed on a wall in linear shear flow. We also investigate the entrapment and cross-flow transport of air bubbles using an oriented hydrophobic strip on a hydrophilic surface. Bubbles creeping along the hydrophobic strip become trapped when reaching its edge where the downstream contact angle changes. When the strip edge is inclined relative to the flow, bubbles creep along the hydrophobic–hydrophilic boundary and thus move in the cross-stream direction. The cross-stream transport of the bubbles strongly depends on the channel Reynolds number and the angle between the hydrophobic strip and the stream. Graphic abstract: [Figure not available: see fulltext.]
  • マイクロバブルによる乱流摩擦抵抗低減
    村井祐一
    ながれ, Vol. 40, pp.252-259 (2021) 40 252 - 259 2021/09 [Refereed][Invited]
  • Ultrasonic Doppler technique for applications in multiphase flow: a review
    C.Tan, Y.Murai, W.Liu, Y.Tasaka, F.Dong, Y.Takeda
    International Journal of Multiphase Flow, Vol. 144, No. 103811 (2021) 144 2021/09 [Refereed][Invited]
  • T.Tanaka, Y.Oishi, H.J.Park, Y.Tasaka, Y.Murai, C.Kawakita
    Ocean Engineering, Vol. 239, No. 109909 (2021) 239 109909 - 109909 0029-8018 2021/09 [Refereed][Not invited]
  • S.Kim, N.Oshima, H.J.Park, Y.Murai
    International Journal of Multiphase Flow, Vol.145, No. 103838 (2021) 145 103838 - 103838 0301-9322 2021/09 [Refereed][Not invited]
  • Ultrasonic velocity profiler applied to explore viscosity-pressure fields and their coupling in ineastic shear thinning vortex streets
    N.Tiwari, Y.Murai
    Experiments in Fluids , Vol. 62, No. 185 (2021) 185 2021/08 [Refereed][Not invited]
  • Bifurcation analysis of bubble-induced convection in a horizontal liquid layer: role of forces on bubbles
    K.Nakamura, H.Yoshikawa, Y.Tasaka, Y.Murai
    Journal of Fluid Mechanics, Vol. 923, R4 (2021) 923 2021/08 [Refereed]
  • Non-intrusive in-line rheometry using ultrasonic velocity profiling
    Y.Tasaka, T.Yoshida, Y.Murai
    Industrial and Engineering Chemistry Research, Vol. 60, pp.11535-11543 (2021) 60 11535 - 11543 2021/07 [Refereed][Not invited]
  • In situ color-to-depth caliburation: toward practical three-dimensional color particle tracking velocimetry
    D.Noto, Y.Tasaka, Y.Murai
    Experiments in Fluids, Vol. 62, No. 131 (2021) 2021/05 [Refereed][Not invited]
  • Coupling structures of two-layer natural convection in a cylindrical vessel investigated by simultaneous two-layer visualization
    D.Noto, Y.Tasaka, Y.Murai
    Experimental Thermal and Fluid Science, Vol.127, No. 110394(2021 2021/04 [Refereed]
  • Bubble fragmentation dynamics in a subsonic Venturi tube for the design of a compact microbubble generator
    Y.Murai, Y.Tasaka, Y.Oishi, P.Ern
    International Journal of Multiphase Flow, Vol. 139, No.103645(2021) 2021/03 [Refereed]
  • H.J.Park, S.Yamagishi, S.Osuka, Y.Tasaka, Y.Murai
    Experiments in Fluids 62 (4) 0723-4864 2021/02 [Refereed][Not invited]
  • Murai Yuichi, HORIMOTO Yasufumi, PARK Hyun Jin, TASKA Yuji, OISHI Yoshihiko, NAGATA Harunori
    The Proceedings of Conference of Hokkaido Branch 一般社団法人 日本機械学会 2021.58 1312  2021
  • Yuichi MURAI, Takahiro UMEMURA, Ryosuke SAYAMA, Yasufumi HORIMOTO, Hyun Jin PARK, Yuji TASAKA, Shuji OTOMO
    The Proceedings of the International Conference on Power Engineering (ICOPE) 2021.15 2021 - 0183 2021
  • S.Nomura, J.Hitomi, Y.Murai, D.C.Giovanni, Y.Tasaka, Y.Takeda, H.J.Park, H.Sakaguchi
    International Journal of Multiphase Flow 136 2021/01 [Refereed][Not invited]
  • N.Tiwari, Y.Tasaka, Y.Murai
    Flow Measurement and Instrumentation 77 2021/01 [Refereed][Not invited]
  • Y.Oishi, Y.Murai, Y.Tasaka
    International Journal of Heat and Fluid Flow 86 2020/12 [Refereed][Not invited]
  • S.Kim, N.Oshima, Y.Murai, H.Park
    Journal of Fluid Science and Technology 15 (3) JFST0020 - JFST0020 2020/12 [Refereed][Not invited]
  • Kotaro Nakamura, Harunori N. Yoshikawa, Yuji Tasaka, Yuichi Murai
    PHYSICAL REVIEW E 102 (5) 2470-0045 2020/11 [Refereed]
     
    We investigate with a linear analysis the stability of a horizontal liquid layer subjected to injection of gas bubbles through a bottom wall. The injection is assumed uniform in space and constant in time. Injected bubbles ascend in the liquid layer due to the Archimedean buoyancy force and are ejected from the top free surface of the liquid layer. Modeling this two-phase flow system as two interpenetrating liquid and gas continua, we show that homogeneous upward gas flows become unstable at large gas fluxes. We determine the critical conditions of this homogeneous-heterogeneous regime transition and show that the critical modes are made of stationary convection rolls, either multi- or whole-layered depending on liquid viscosity, the radius of bubbles, and the thickness of liquid layer. By examining the energy transfer from base to perturbation flows, we indicate that liquid convective motion is driven by the buoyancy on heterogeneously distributed bubbles. We also reveal that the lift forces on bubbles have significant stabilizing effects by homogenizing bubble distribution close to the bottom wall.
  • Atsuhide Kitagawa, Yuriko Shiomi, Yuichi Murai, Petr Denissenko
    EXPERIMENTS IN FLUIDS 61 (11) 0723-4864 2020/10 [Refereed]
     
    This paper presents an experimental study of horizontal channel flow with air-filled superhydrophobic grooves. Air-water interfaces in the grooves are visualized in a range of the channel Reynolds number, Re, (2000 <= Re <= 5000) while flow characteristics are evaluated using particle tracking velocimetry measurements at Re=3000 and 4000. Near the air-water interface in the superhydrophobic groove, turbulent eddies and hence the Reynolds shear stress appreciably attenuate owing to a lack of energy supply through the interface, and it takes a notable distance for the Reynolds shear stress to recover downstream of the groove. Additionally, a secondary cross-flow from the solid surface region between two grooves towards the air-water interface appears and sweeps eddies between the grooves towards the interface. The decay of turbulent eddies and the sweeping of eddies from the solid surface to the air-water interface reduce friction drag both in and immediately downstream of the grooved region.
  • Taiji Tanaka, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    OCEAN ENGINEERING 214 107850 - 107850 0029-8018 2020/10 [Refereed][Not invited]
     
    Although the practical use of bubbly drag reduction for marine vessels has begun to spread, it is unclear how bubbles migrate along spatially developing turbulent boundary layers. We measured the spatiotemporal distribution of the local void fraction beneath a 4-m-long fully transparent flat-bottom model ship towed in a 100-m-long water tank with a ship speed of up to 3.00 m/s. Bubbles were injected with both constant and periodically fluctuated air flow rates into the turbulent boundary layers. With constant flow rates, 2-5-mm bubbles caused spontaneous void waves, i.e., quasiperiodic fluctuation of the local void fraction, standing at 4-8 Hz. When repetitive bubble injection, which formed artificial void waves downstream, was applied, void waves propagated at 47%-53% of the ship speed. During the propagation, we found the apparent diffusion coefficient of the void wave taking values down to 10(-4) m(2)/s and even negative values when the repetition frequency was set lower than the spontaneous frequency of void waves. This indicates that the void waves persist for several tens of meter in application to ship hulls.
  • Applicability evaluation of the stress-optic law in Newtonian fluids toward stress field measurements
    D.Noto, Y.Tasaka, J.Hitomi, Y.Murai
    Physical Review Research 2 2020/09 [Refereed][Not invited]
  • Y.Murai, H.Sakamaki, I.Kumagai, H.Park, Y.Tasaka
    Ocean Engineering 216 2020/08 [Refereed][Not invited]
  • Kodai Fujita, Yuji Tasaka, Takatoshi Yanagisawa, Daisuke Noto, Yuichi Murai
    JOURNAL OF VISUALIZATION 23 (4) 635 - 647 1343-8875 2020/08 [Refereed][Not invited]
     
    To enrich the three-dimensional experimental details of vortex structures in rotating Rayleigh-Benard convection, we established a technique visualizing three-dimensional vortex structures using scanning planar particle image velocimetry. Experiments were performed at fixed Rayleigh number, Ra=1.0x10(7) to 1.0x10(8), corresponding to convective Rossby numbers from 0.1 <= Ro <= 0.5 at which gradual transition between vortical plumes and convective Taylor columns regime is observed. Stream function distributions calculated from horizontal velocity vector fields visualize the vortex structure formed in the regimes. As quantitative information extracted from the visualized structures, distances between vortices recognized on the distributions show a good agreement with that evaluated by a theory. With the accumulated planar stream function distributions and vertical velocity component calculated from the horizontal velocity vectors, the three-dimensional representations of vortices indicate that quasi-two-dimensional columnar vortices straighten in the vertical direction with increasing Ta. Graphic abstract
  • S.Tuckerm K.Igor, Y.Murai, P.Denisenko
    Applied Energy 268 2020/04 [Refereed][Not invited]
  • YOSHIDA Taiki, TASAKA Yuji, MURAI Yuichi
    The Proceedings of the Fluids engineering conference 一般社団法人 日本機械学会 2020 OS01 - 7 2020 

    The dispersed particles make alignments in the sheared direction under unsteady shear flows when the fluid relaxation time is sufficiently long. The alignment changes the effective viscoelasticity because a corded-like pattern of particles functions as a macro-spring effect and reduction of particle interactions. Those experimental findings regarding the effective viscoelasticity of non-Newtonian fluids with spherical particles are found by means of ultrasonic spinning rheometry. Further numerical tests using a simple toy model assuming dispersed particles combined by spring forces considering yield stresses were conducted to clarify factors caused by the particle alignment under unsteady shear flows.

  • Kohei OHIE, Taiki YOSHIDA, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI
    Transactions of the JSME (in Japanese) 2020
  • Shinnosuke Obi, Koji Fukagata, Masaharu Kameda, Chisachi Kato, Yohei Morinishi, Yuichi Murai, Satoshi Watanabe, Masao Watanabe
    JOURNAL OF FLUID SCIENCE AND TECHNOLOGY 15 (2) 1880-5558 2020
  • Toshiki ASHIDA, Yuichi MURAI, Hyun Jin PARK, Yuji TASAKA, Shigeyuki NAGAI
    Transactions of the JSME (in Japanese) 86 (888) 20 - 00184 2020 [Refereed][Not invited]
  • Hyun Jin Park, Shintaro Akasaka, Yuji Tasaka, Yuichi Murai
    IEEE Sensors Journal 1 - 1 1530-437X 2020 [Refereed][Not invited]
  • YOSHIDA Taiki, TASAKA Yuji, OHIE Kohei, MURAI Yuichi
    JAPANESE JOURNAL OF MULTIPHASE FLOW 日本混相流学会 34 (2) 334 - 341 0914-2843 2020 [Refereed][Not invited]
     

    For playing a role of filling a hole in the applicable range of standard rheometer, ultrasonic spinning rheometry (USR) is presented; it is based on equation of motion to explain the fluid rheology and to quantify the rheological properties satisfying the considered equation of motion for complex fluids. Some examples of rheological evaluation for multi-phase fluids using USR were presented; clay dispersion with thixotropy, polymer solution with large-spherical particles, dessert paste with pectin gel including fruit pulps. The efficacy of USR was discussed through those practical tests for complex fluid.

  • Hyun Jin Park, Daichi Saito, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 109 0894-1777 2019/12 [Refereed][Not invited]
     
    Three-dimensional distribution of microbubbles dispersed in a turbulent boundary layer spatially developing along a flat plate is investigated experimentally. The aim of study is to find out visually how microbubbles interact with turbulent eddies to achieve frictional drag reduction on a wall. Setting conditions of the experiments are stream Reynolds number up to 2.3 x 10(4), microbubble volume fraction inside boundary layer less than 10(-5), and microbubble Stokes number smaller than 10(-3). Stream-wise vortices in the boundary layer were visualized by flake optics, of which spacing expands with injection of microbubbles. 3-D microbubble distributions were visualized by a color-coded volumetric illumination. The result showed preferentially accumulated microbubble clouds to low-speed streaks close to viscous sublayer and to hair-pin vortices in the buffer layer, leading to reduced diffusivity of microbubbles relative to the turbulent momentum diffusivity.
  • Tomoaki Watamura, Atsuhide Kitagawa, Yuichi Murai
    CHEMICAL ENGINEERING SCIENCE 208 115132  0009-2509 2019/11 [Refereed][Not invited]
     
    To elucidate the motion of spatiotemporally developing flow structures driven by densely concentrated microbubbles, we experimentally investigated the distribution and motion of microbubbles rising along a vertical plane wall. We performed optical measurements and an ultrasonic velocity profiling to determine the distribution and motion of microbubbles. We found that the microbubbles form clouds (fluid blobs containing rich microbubbles) with a three-dimensional structure, the spatial patterns of which become more periodic in the streamwise direction than in the spanwise direction. In addition, owing to the coalescence of neighboring microbubble clouds caused by the hydrodynamic interaction between them, the separation length of the buoyant force distribution of microbubbles increases with increasing the distance from the bottom of the tank. According to the Reynolds number of the microbubbles cloud presented here, we conclude that the unsteady motion of microbubble clouds can be analogously modeled as an interacting motion of moving bodies in flow. (C) 2019 Elsevier Ltd. All rights reserved.
  • Yoshihiko Oishi, Yuichi Murai, Yuji Tasaka
    JOURNAL OF VISUALIZATION 22 (5) 867 - 876 1343-8875 2019/10 [Refereed][Not invited]
     
    A single vortex ring subject to background rotation in the process of wall impingement has been experimentally investigated by particle tracking velocimetry (PTV). Two parameter conditions of Reynolds and Rossby numbers were chosen in addition to stationary environment as much strong and competitive Coriolis force emerges in comparison with inertia induced by vortex rings. From horizontal PTV windows set on the rotating experimental frame above the bottom wall, comprehensive influences of Coriolis force on the wall-impinging reaction are visualized as space-time three-dimensional vorticity distributions. Against natural growth of azimuthal waves due to Widnall instability, wall-impinging suppresses the waves and rather re-organizes original primary vortex because of cyclonic swirl coherently induced during impingement. This resists to turbulent collapse of vortex ring during the impingement and self-boosts own life time. We try to explain the mechanism of such an anti-decaying process in the final part, untangling the phenomenon with best read from the space-time correlations among three vorticity components.
  • Anubha Garg, Chandrima Shrivastava, Yuichi Murai, Erich J. Windhab
    PHYSICS OF FLUIDS 31 (10) 107109  1070-6631 2019/10 [Refereed][Not invited]
     
    The complex airflow in convection ovens directly influences the heat transferred to the product placed inside, thereby affecting product quality. Characterization of related airflow profiles can provide scientific understanding for improvement of oven designs as well as important parameters for simulation of involved thermal processes. In this study, the particle-imaging velocimetry (PIV) technique was applied to visualize airflow inside a household convection oven with samples placed at three different locations on a baking tray. The oven cavity was modified for optical access, and airflow was measured at room temperature. A 30 mW green laser was used for illuminating tracer particles in a laser sheet that were generated using incense sticks. The flow patterns were captured using a high-speed camera at 1000 fps. The vorticity and turbulent kinetic energy parameters derived from velocity fields reflected adequate mixing of air inside the cavity. The computed heat transfer coefficient distribution from the boundary layer flow fields to the sample surface ranged between 2.0 and 183 W m(-2) K-1. The results showed separation of the laminar boundary layer from the object surface at angles of 85 degrees -90 degrees. The PIV-algorithms and boundary layer flow derived parameters developed in this study can be used for refined characterization of complex air or gas flows and related heat transfer characteristics in closed cavity convection ovens and the like arrangements. Published under license by AIP Publishing.
  • Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    PHYSICS OF FLUIDS 31 (10) 103304  1070-6631 2019/10 [Refereed][Not invited]
     
    The effective viscoelasticity of non-Newtonian fluids with spherical particles has been examined by ultrasonic spinning rheometry [Yoshida et al., "Efficacy assessments in ultrasonic spinning rheometry: Linear viscoelastic analysis on non-Newtonian fluids," J. Rheol. 63, 503 (2019)]. Under unsteady shear flows, the dispersed particles make alignments in the sheared direction if the relaxation time of the fluid media is sufficiently long. The alignments modulate the effective rheological properties, and the effective viscosity does not reach the value estimated by Einstein's law; the effective elasticity increases significantly with increasing volume fraction in the bulk of the measurement volume. To establish further details of factors influencing the aligned particles under unsteady shear flows/deformations, numerical tests using a simple toy model assuming dispersed particles combined by spring forces considering yield stresses were conducted, and the model identified the importance of the relaxation process on the orientation of the particles. Finally, considering the experimental findings, local and macrorheological characteristics are strongly modulated by the particle alignment when the test fluid media have long relaxation times (or high Weissenberg numbers). Published under license by AIP Publishing.
  • Bubble clustering in a horizontal turbulent channel flow investigated via bubble-tracking velocimetry
    Y.Oishi, Y.Tohge, Y.Murai, Y.Tasaka
    International Journal of Multiphase Flow 111 2019/09 [Refereed][Not invited]
  • Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    JOURNAL OF RHEOLOGY 63 (4) 503 - 517 0148-6055 2019/07 [Refereed][Not invited]
     
    We have progressively developed an ultrasonic spinning rheometry (USR) that has the potential to visualize complex details of rheology, such as time-dependence, coexistence of gel and sol, effective viscosity of multiphase fluids, and other particulars. This rheometry makes it possible to overcome the main issues in conventional rheometry, originating from nonideal velocity profiles in the complex fluids. The most notable advantage of USR is the ability to perform "local" rheological evaluations from only the velocity information for a short-time period by solving the equation of motion. This benefit is provided while avoiding noise augmentations by introducing a linear viscoelastic analysis in the frequency domain. Solving the equation of motion with a rheological model equation in the frequency domain, multiple rheological parameters are quantified by minimizing the cost function. In this paper, the analysis presented by USR is verified by comparative experiments using a rheometer with the typical geometry of parallel disks. As a complementary technique for conventional rheometers, the USR efficacies are shown through rheological assessments for Newtonian, shear-thinning, and thixotropic fluids. Additionally, USR can provide instantaneous flow curves O(1 s) that lead to understanding the rheology in complex fluids with time-dependency. (C) 2019 The Society of Rheology.
  • Thermal diffusion interface inside a horizontal pipe flow compared between laminar and turbulent flow regimes
    K.Nakamura, H.J.Park, Y.Murai, T.Takeuchi
    Journal of Visualization 22 809 - 818 2019/06 [Refereed][Not invited]
  • Neetu Tiwari, Yuji Tasaka, Yuichi Murai
    FLOW MEASUREMENT AND INSTRUMENTATION 67 23 - 32 0955-5986 2019/06 [Refereed][Not invited]
     
    A novel algorithm of pressure field estimation based on ultrasound velocity profiler (UVP) is developed. The method consists of UVP measurement of velocity distribution in fluid flows and numerical analysis of the measured data using fluid dynamics equations. We introduce equation of continuity, incompressible Navier-Stokes equation and proper orthogonal decomposition (POD) into the basic algorithm, so that pressure field of space-time two-dimensional unsteady fluid flow is fully reconstructed. Since UVP is based on ultrasound Doppler principle, the local instantaneous pressure distribution is obtained non-intrusively. The performance of an algorithm is evaluated for vortex shedding flow behind a circular cylinder at Re = 1000. Considering the specification of UVP, the optimal method of experimental data conversion to pressure information is proposed. We have found that the one-dimensional velocity measurement by UVP upon Taylor's frozen hypothesis is suitable for evaluation of pressure field in wake of the cylinder. The present algorithm is also demonstrated for opaque fluid flows by considering vortex flow in milk.
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 104 141 - 152 0894-1777 2019/06 [Refereed][Not invited]
     
    This paper presents experimental findings on the behavior of bubbles moving along upper flat plates with different surface wettability in a horizontal channel. The size and velocity of the bubbles are measured by image processing to evaluate the wettability dependence in the range of channel Reynolds number, Re (2000 <= Re <= 5000) and bubble Weber number, We (1 < We < 10). When the bubbles move along a hydrophilic flat plate, their wall-sliding velocity increases with the bubble diameter, and no bubbles adhere to the plate even at low Re. By contrast, their behavior depends strongly on Re when a hydrophobic plate is used. At Re = 5000, an intrinsic cycle of coalescence and breakup of bubbles takes place. In this cycle, large wall-creeping bubbles become stretched by shear, and then each tends to break up into a small bubble that adheres to the plate surface and a medium-sized bubble that is detached from the plate. Because the small, adhered bubbles grow to large creeping bubbles through coalescence with bubbles supplied upstream, this intrinsic cycle repeats downstream. As a consequence, the hydrophobic plate produces two groups of bubbles within the turbulent boundary layer of the plate: one consisting of medium-sized free bubbles and one consisting of small wall-adhering bubbles to large wall-creeping bubbles.
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 103 66 - 77 0894-1777 2019/05 [Refereed][Not invited]
     
    Frictional drag reduction due to bubble lubrication was investigated by measuring liquid films creeping along a wall within a two-phase turbulent boundary layer. We developed noninvasive time-resolved ultrasonic pulse echography for imaging a liquid film at a profiling rate of 3 kHz and a spatial resolution of 50 Various film patterns were obtained for a 4-m-long flat-bottom model ship towed in a 100-m-long water tank, where a drag reduction rate of 30% was recorded for maximum air injection. We found that the liquid-film thickness ranged from 50 to 150 wall units of the single-phase turbulent boundary layer; this film was thicker than the buffer layer depth. With an increase in the air injection flow rate, the average thickness decreased close to the buffer layer limit while the skewness and kurtosis of the probability density function of the film thickness increased. A sudden transition of the film form was detected according to the kurtosis, allowing the monitoring of the criteria of the coalescence of dispersed bubbles into large elongated bubbles via ultrasonic pulse echography.
  • Horizontal diffusive motion of columnar vortices in rotating Rayleigh-Bénard convection
    D.Noto, Y.Tasaka, Y.Murai, T.Yanagisawa
    Journal of Fluid Mechanics 871 401 - 423 2019/04 [Refereed][Not invited]
  • Megumi Akashi, Takatoshi Yanagisawa, Yuji Tasaka, Tobias Vogt, Yuichi Murai, Sven Eckert
    PHYSICAL REVIEW FLUIDS 4 (3) 2469-990X 2019/03 [Refereed][Not invited]
     
    Turbulent Rayleigh-Benard convection was investigated within a liquid metal layer, Prandtl number Pr = 0.03, in a square vessel having a moderate aspect ratio, Gamma = 5. Laboratory experiments were performed at moderate Rayleigh numbers, 7.9 x 10(3) < Ra < 3.5 x 10(5). Ultrasonic velocity profiling was used to visualize the spatiotemporal flow structure in two horizontal planes, while temperature fluctuations were monitored simultaneously in the fluid layer. By using multiple ultrasonic sensors, a grid of orthogonal measurement lines was created. This configuration enabled the identification of coherent flow structures showing periodic oscillations. In particular, oscillatory roll-like structures were observed for Ra less than or similar to 6 x 10(4), while the transition to a new-found, fully three-dimensional cellular structure occurs around Ra = 7 x 10(4). The Fourier analysis of the temperature fluctuations indicates that the convection reaches the developed state of thermal turbulence at this Ra number. This cellular structure of the flow field is recognized as a representation of the large-scale circulation in thermal turbulence for the specific situation of confined convection in the rectangular vessel. The transition from laminar convection to thermal turbulence manifests itself in the occurrence of unstable intermediate regimes accompanied by a stepwise increment in the horizontal scale. We suggest scaling laws for the characteristic velocity and the dominating oscillation frequency and based on that for the horizontal length scale as a function of the Ra number. The comparison to corresponding values of characteristic length scales published for thermal convection in air in larger aspect ratios [Pr = 0.7, T. Hartlep et al., Phys. Rev. Lett. 91, 064501 (2003), A. Pandey et al., Nat. Commun. 9, 2118 (2018), and D. E. Fitzjarrald, J. Fluid Mech. 73, 693 (1976)] reveals a different Ra number dependence of the horizontal wave number.
  • Xuewei Shi, Chao Tan, Feng Dong, Yuichi Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 111 219 - 231 0301-9322 2019/02 [Refereed][Not invited]
     
    As a highly complex and random process, oil-gas-water three-phase flow is commonly encountered in petroleum production and transportation. Flow velocity of each individual phase is an important parameter for production estimation and flow assurance. To measure the phase velocity of three-phase flow, a one-side ultrasonic transducer working in continuous wave Doppler mode and a conductance sensor were combined to obtain the Doppler shift signal and the holdup signal. Firstly, the water holdup fluctuations were decomposed by the continuous wavelet transform to get the local wavelet energy (LWE) coefficients map on the time-frequency diagram to characterize the local flow structures of each typical flow regime. Since the ultrasound was reflected and scattered by both liquid droplets and gas bubbles, the Doppler shift signal contains fluctuations in different scales. The Doppler shift signal was then processed by the short-time Fourier transform to reveal the correlation between the time-varying velocity characteristics and the flow structure. Thirdly, the ensemble empirical mode decomposition was used to decompose the Doppler shift signal into different intrinsic mode functions (IMFs), and the first three IMFs were selected as the main IMFs. Finally, combined with the LWE coefficient map to jointly analyze the flow dynamic characteristics, the specific IMFs were found well-correlated with the flow information of the specific phases. The models for phase velocities extraction were then established. The extraction results were validated through dynamic experiments. The root mean square error of the liquid superficial velocity, the gas superficial and the overall superficial velocity are 0.06 m/s, 0.06 m/s and 0.07 m/s respectively. (C) 2018 Elsevier Ltd. All rights reserved.
  • Yuichi Murai, Daichi Saitoh, Daiki Ushiyama, Hyun Jin Park, Yuji Tasaka
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 2019 
    How microbubbles behave inside turbulent boundary layers are investigated experimentally. Water electrolysis is applied for generation of microbubbles in water, of which electrodes are flash mounted on the solid wall in the upstream section of the measurement area. Four kinds of solid surfaces are examined to compare the microbubble distribution. For a circular cylinder of the radius R= 22 mm at Re=5,000, we found that microbubbles depart from the surface earlier than the liquid boundary layer. For an elliptic cylinder of the curvature radius of R=60 mm and a hydrofoil of NACA0040, microbubble injection made the separation point move downstream in the range of 9,000< Re< 90,000. To compare the effect with the cases of flat solid surfaces (R=infinity), we visualized three-dimensional distribution of microbubbles with color-coded volumetric illumination technique. The result has shown formation of microbubble clusters intermittently, which has Coulomb potential due to negative electric charge on bubble interfaces.
  • Taiji Tanaka, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 2019 
    To investigate the development process of a void wave, spatio-temporal fluctuation of void fraction, we examined experimentally a turbulent boundary layer with bubble injections. The experiments performed on a flat bottom of 4-m-long transparent model ship towed in a tank of 100 m length with the speed of up to 3.00 m/s. In bubbles injection with constant air flow rate, void fluctuations with 4 Hz or 8 Hz appeared dependent on the towing speed. With periodically fluctuated air flow rate, artificial void waves were provided into the turbulent boundary layer and their frequency was maintained during the downstream propagation. The attenuation rate of the fluctuation evaluated using Fourier analysis of the wave took the minimum value at specific injection frequency conditions.
  • Hyun Jin Park, Yuhei Sugano, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 4 2019 
    In this paper, we introduce an imaging technique for capturing 3-imensional smoke density distribution by adopting a three-layer color illumination and a six-layer color illumination for air flow measurements. A camera capable to capture three primary color components (red, green, blue) and a liquid crystal display projector are used as optical equipment. Each color layer is aligned parallel to a photographed plane of the video camera. The present technique assumes two things three primary color signals are received proportionally to smoke density in each color layer and there is a linear relation between the smoke density and the color signals. These assumptions allow that the smoke density can be obtained from the color signals by solving inverse problem. In the three-layer case, solving inverse problem is possible by these assumptions. In the six-layer color illumination, a color layer illumination consisting of three primary colors and their intermediate colors (yellow, cyan, magenta) are projected toward measurement space. This forms an inverse problem with lack of information to reconstruct the smoke density because the number of independent color signals is lower than the number of color layers. To fix this issue, we apply a method to increase the number of color signals in time direction by switching two different illumination patters. The number of color signals becomes six to be equal to the number of variables to solve algebraically.
  • TASAKA Yuji, YOSHIDA Taiki, MURAI Yuichi
    The Proceedings of the Fluids engineering conference 一般社団法人 日本機械学会 2019 OS11-01  2019 [Not refereed]
  • NAKAMURA Hayato, OISHI Yoshihiko, KAWAI Hideki, MURAI Yuichi, KAWAKITA Chiharu, HAMADA Tatsuya
    The Proceedings of the Fluids engineering conference 一般社団法人 日本機械学会 2019 (0) OS2 - 19 2019 

    We measured fluctuations of turbulent shear stress in a horizontal bubbly channel flow. In this research, simultaneous measurement of wall shear stress by a new shear stress sensor using laser Doppler principle and visualization for bubble image by high-speed camera were performed. In order to investigate the relationship between the instantaneous change of shear stress and the passage of bubbles, we evaluated the variation of time series data of the shear stress and the passage distribution of bubbles by analyzing high-order moment and quadrant classification. As a result, it was found that the relationship between the fluctuation of shear stress and the frequency of bubble passage was altered as injection method of bubbles was changed from continuous to repetitive injection. We have confirmed a phenomenon peculiar to repetitive bubble injection, i.e. the shear stress decreased during no bubble passes by. It was also found that the relationship was reversed as the injection frequency of bubbles ranged from 2 to 4 Hz.

  • MURAI Yuichi, Otomo Shuji, TASAKA Yuji, Denissenko Petr
    The Proceedings of the National Symposium on Power and Energy Systems 一般社団法人 日本機械学会 2019 (0) C211  2019 
    Influence of high-intensity turbulence to the performance of a Savonious wind turbine has been investigated experimentally. The turbulent intensity and its isotropic quality are managed in a large wake region of an open-jet type wind tunnel. We have found that the rotational speed of the turbine rather increases with hep of turbulence as a constant load was subject to the turbine. This robustness to the inflow quality is attributed to the drag acting on the blade being intensified by the turbulence. Hot-wire anemometer measurement of the flow behind the turbine revealed that periodic vortex-shedding due to the blade-passing frequency was suppressed with strong turbulence in the inflow.
  • TANAKA Taiji, PARK Hyun Jin, TASAKA Yuji, MURAI Yuichi, KAWAKITA Chiharu
    The Proceedings of the National Symposium on Power and Energy Systems 一般社団法人 日本機械学会 2019 (0) A122  2019 [Refereed][Not invited]
  • Ichiro Kumagai, Kakeru Taguchi, Chiharu Kawakita, Tatsuya Hamada, Yuichi Murai
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 2019 [Refereed][Not invited]
     
    Copyright © 2019 ASME. Air entrainment and bubble generation by a hydrofoil bubble generator for ship drag reduction have been investigated using a small high-speed channel tunnel with the gap of 20 mm in National Maritime Research Institute (NMRI). A hydrofoil (NACA4412, chord length = 40 mm) was installed in the channel and an air induction pipe was placed above the hydrofoil. The flow rate of the entrained air was quantitatively measured by thermal air flow sensors at the inlet of the air induction pipe. The gas-liquid flow around the hydrofoil was visualized by a backlight method and recorded by a high-speed video camera. As the flow velocity in the channel increased, the negative pressure generated above the suction side of the hydrofoil lowered the hydrostatic pressure in the channel, then the atmospheric air was entrained into the channel flow. The entrained air was broken into small air bubbles by the turbulent flow in the channel. The threshold of air entrainment, the air flow rate, and gas-liquid flow pattern depends on Reynolds number, angle of attack (AOA), and hydrofoil type. We identified at least three modes of air entrainment behavior: intermittent air entrainment, stable air entrainment, and air entrainment with a ventilated cavity. At high flow speed in our experimental condition (9 m/s), a large volume of air bubbles was generated by this hydrofoil system (e.g. air flow rate was 50 l/min for NACA4412 at AOA 16 degrees), which has a high potential to reduce ship drag.
  • Daisuke Noto, Yuji Tasaka, Takatoshi Yanagisawa, Hyun Jin Park, Yuichi Murai
    JOURNAL OF VISUALIZATION 21 (6) 987 - 998 1343-8875 2018/12 [Refereed][Not invited]
     
    We established a vortex detection method using instantaneous temperature fields that were visualized using thermochromic liquid crystals (TLCs) to investigate behaviors of vortical structures in a rotating Rayleigh-Benard convection. Experimental testing was performed at a fixed Rayleigh number in water containing encapsulated TLCs. Vortices were recognized as undulations that appear in the horizontal temperature fields, thus making vortex detection with high spatial resolution possible, and this enabled quantitative investigation of the dynamics of vortical structures. Standard template matching was used to detect individual vortices on visualized temperature fields, and two-dimensional curved surface fitting was adopted to remove erroneous detections and to evaluate shapes of local temperature fields corresponding to vortical structures. Additionally, vortex tracking clearly showed geometric advection pattern of vortical structures.
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    EXPERIMENTS IN FLUIDS 59 (11) 0723-4864 2018/11 [Refereed][Not invited]
     
    Frictional drag reduction, a technique by which bubbles are injected into the turbulent boundary layer surrounding the hull of a marine vessel, is now at the stage of practical applications. In achieving drag reduction, void waves often stand out naturally, the reason for which still remains unclear. The present study aims at an experimental characterization of void waves along a flat-bottom ship. A 100-m-long water reservoir is used in which a 4-m-long fully transparent experimental model ship, equipped with wall shear stress sensors and cameras, is towed by a train at speeds of up to 3m/s. From measurements of the transition of the bubble distribution from random to wavy accumulated swarms downstream, the accompanying intrinsic passing frequency of void waves is examined. A 30% drag reduction rate was recorded with the appearance of void waves in the boundary layer at an average void fraction of 4%. This is much greater than the trivial inertia effect from drag reduction. To clarify the characteristics of the measured void waves, we compare the void wave frequency range to those of several flow instabilities that may occur in bubbly two-phase boundary layer flows.
  • Yuichi Murai, Yuji Tasaka, Yoshihiko Oishi, Yasushi Takeda
    EXPERIMENTS IN FLUIDS 59 (11) 0723-4864 2018/11 [Refereed][Not invited]
     
    Injection of bubbles into Taylor-Couette flow creates new flow modes which have not been experienced in single-phase flow conditions. An array of spiral vortices array is one such mode departing from the original toroidal Taylor vortices. The aim of the present study is to explore the mode transition of the two-phase flow using particle tracking velocimetry. Vertical-axis concentric cylinder with a rotating inner cylinder was used to measure the motion of both phases in the range 600
  • Yuichi Murai, Gretar Tryggvason
    NUCLEAR ENGINEERING AND DESIGN 337 317 - 317 0029-5493 2018/10
  • Accuracy and robustness evaluations on algorithms of ultrasonic spinning rheometry
    Taiki Yoshida, Yuji Tasaka, Hyun Jin Park, Yuichi Murai
    11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering 2018/09 [Refereed][Not invited]
  • Weiling Liu, Chao Tan, Xiaoxiao Dong, Feng Dong, Yuichi Murai
    IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT 67 (9) 2129 - 2142 0018-9456 2018/09 [Refereed][Not invited]
     
    Oil-water two-phase flow commonly exists in many industries. The accurate measurement of flow velocity is beneficial for safety operation and economic efficiency. A combination of a pulse-wave ultrasonic Doppler (PWUD) sensor and a conductance/ capacitance (CCC) sensor is proposed for flow velocity measurement in dispersed oil-water two-phase flow. The PWUD sensor estimates dispersed phase velocity', and the CCC sensor provides phase fraction. The overall superficial flow velocity (J) and individual flow velocities are estimated by combining the outputs of the two sensors. The dual-modality sensing system was designed and experimentally verified on a horizontal multiphase flow loop. Ignoring the slippage between two phases, the J is estimated with an average relative error (ARE) of 5.58%, water superficial velocity with 6.42%, and oil superficial velocity with 6.91%. To further improve the measurement accuracy, slip velocity-based measurement model is presented by introducing the drift-flux model. The distribution parameter of this model is derived from theoretical analysis. The correlation between relative velocity and J is analyzed by the force analysis of dispersed phase in water/oil-continuous flow theoretically and experimentally. The results demonstrate that the proposed model estimates the J with an ARE of 2.21%, water superficial velocity with 3.56%, and oil superficial velocity with 3.80%. Besides, ARE of different flow patterns shows a uniform distribution. The slip velocity-based measurement model has an advantage of less error in overall superficial flow velocity estimation, reduced by 60% compared with that of the nonslip velocity-based measurement model.
  • Rheological properties of montmorillonite dispersions in dilute NaCL concentration investigated by ultrasonic spinning rheometry
    T.Yoshida, Y.Tasaka, S.Tanaka, H.J.Park, Y.Murai
    Applied Cray Science, Vol.161, pp.513-523 2018/04 [Refereed][Not invited]
  • Taiki Yoshida, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hiroki Teramura, Shigenobu Koseki
    JOURNAL OF VISUALIZATION 21 (2) 253 - 265 1343-8875 2018/04 [Refereed][Not invited]
     
    We proposed a novel ultrasonic Doppler-echo visualization method that is expected to realize nondestructive visualization using an ultrasonic velocity profiler. The visualization uses information of both the Doppler velocity and echo intensity that have usually been used by the ultrasonic velocity profiler to obtain instantaneous velocity profiles. The feasibility of the method is confirmed by measurements of a rubber ball, apple, and tomato having different acoustic impedances, pulp hardnesses, shapes, and inner structures. Mathematical relations and image processing parameters were discussed to obtain images of the inner structures of test objects using the ultrasonic velocity profiler. Trial measurements of test objects elucidated that the Doppler velocity and echo intensity detect different features of the test objects. Using the Doppler velocity and echo intensity, the outlines and inner structures of the objects can be visualized.
  • Yuji Tasaka, Taiki Yoshida, Richard Rapberger, Yuichi Murai
    RHEOLOGICA ACTA 57 (3) 229 - 240 0035-4511 2018/03 [Refereed][Not invited]
     
    To achieve a stable evaluation of the linear viscoelasticity of bubble suspensions, which have difficulties for conventional rheometers from spatial distributions of rheological properties with bubble deformations, we proposed a novel rheometry based on spatio-temporal velocity data obtained by ultrasonic velocity profiling (UVP). A frequency-domain algorithm was adopted to overcome a critical influence of measurement noise on the rheological assessment, which is inferred from error propagation characteristics through the equations of motion in discretized form. Applicability and advantage of the present rheometry with the frequency-domain algorithm were verified by two kinds of fluids: high viscous oil as a Newtonian fluid and polyacrylamide aqueous solution as a shear thinning, viscoelastic fluid. The rheometry was finally adopted for bubble suspensions subject to high oscillatory shear, and it could validly extract elasticity-originated momentum transfer as a function of space.
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 113 1200 - 1211 0017-9310 2017/10 [Refereed][Not invited]
     
    Natural convection heat transfer from a heated wall in water with near-wall injection of millimeter-sized bubbles is studied experimentally. Velocity and temperature measurements are conducted in the near wall region. In the range of the heated wall angles from 0 to 417 from the vertical, the heat transfer coefficient increases by up to an order of magnitude with bubble injection. The ratio of the heat transfer coefficient with bubble injection to that without injection increases with the wall inclination angle. Based upon measured liquid temperature distributions and liquid flow velocity profiles, enhancement of heat transfer by bubble injection is explained by two mechanisms. First, wall-parallel transport of cold liquid into the thermal boundary layer is enhanced by the bubble-driven flow. Second, wall-normal mixing of warm liquid and cold liquid occurs, as a result of wall-normal velocity fluctuations of the liquid phase activated by a combination of bubble rising motion, vortex shedding from the bubbles, and unsteady vortices formed within the boundary layer. The unsteady vortices travel along the wall together with the bubbles, primarily contributing to the enhancement of heat transfer at higher wall inclination angles. (C) 2017 Elsevier Ltd. All rights reserved.
  • Bruno van Ruymbeke, Yuichi Murai, Yuji Tasaka, Yoshihiko Oishi, Celine Gabillet, Catherine Colin, Noureddine Latrache
    JOURNAL OF VISUALIZATION 20 (2) 349 - 358 1343-8875 2017/05 [Refereed][Not invited]
     
    We develop a novel method to study the gas phase features in a bubbly Taylor-Couette flow when bubbles are arranged as elevated toroidal strings. The flow is recorded in the front view plane with a highspeed camera for a Reynolds number of 1500 and a global void fraction of 0.14 %. An image processing algorithm is developed to discriminate bubbles accumulated in clouds near the inner cylinder (cloud bubbles) from bubbles trapped in the bulk flow by vortices (swirl bubbles). The analysis of the preferential positions, azimuthal velocities, and equivalent void fraction of clouds and swirl bubbles separately provides a new insight into the dynamics of the bubble's entrapment.
  • Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    JOURNAL OF RHEOLOGY 61 (3) 537 - 549 0148-6055 2017/05 [Refereed][Not invited]
     
    We propose a rheometry using ultrasonic velocity profiling (UVP) that visualizes and evaluates quantitatively opaque complex fluids in a cylindrical open vessel performing unsteady rotation. The methodology termed "ultrasonic spinning rheometry (USR)" is expected to provide details of various rheological properties. In our study of USR applications, an enhancement in measuring some rheological properties was achieved for three different non-Newtonian fluids. For quantitative evaluations, we focused on momentum propagation in unsteady shear flows from an oscillating cylindrical container. In such flows, this propagation is represented in the radial profiles of the phase lag of velocity fluctuations. The phase lag information is obtained by a discrete Fourier transform of the spatio-temporal velocity distributions measured using UVP and indicates that the phase lag changes substantially as rheological properties change in a test fluid. As the primary rheological property, a local effective viscosity that is representative of the Newtonian viscosity in the bulk of a measurement volume is determined using UVP. In addition, the shear stress distribution, yield stress, spatial viscosity profile, and shear modulus are obtained as secondary rheological properties. (C) 2017 The Society of Rheology.
  • 中村幸太郎, 田坂裕司, 村井祐一
    混相流, Vol. 31 2017/04 [Refereed][Not invited]
  • Kotaro Nakamura, Yuji Tasaka, Yuichi Murai
    Japanese Journal of Multiphase Flow 31 (1) 20 - 28 2017/01 [Refereed][Not invited]
  • Junpei Hitomi, Yuichi Murai, Hyun Jin Park, Yuji Tasaka
    IEEE ACCESS 5 15021 - 15029 2169-3536 2017 [Refereed][Not invited]
     
    The combined use of ultrasound pulse-echo intensity and Doppler shift frequency is examined as a means to measure strong unsteady three-phase pipe flows of a gas and two liquids. With air, oil, and water as components of the fluid media, particular attention is given to analyze ultrasound responses at the air-oil and oil-water interfaces. Reciprocating slugging is generated inside a 55-mm-diameter circular pipe, of which edges oscillate vertically at a controlled frequency. We use an ultrasound velocity profiler to obtain the 1-D cross-sectional distributions of the instantaneous flow velocity at the sampling rate of 60 Hz. All the measurements are realized by a single ultrasound transducer located outside the pipe. Measurement accuracy is validated using a high-speed camera coupled with particle image velocimetry that is synchronized with the profiler. The results demonstrate that the proposed technique works properly in sensing both interfaces as well as in-phase flow velocity distributions. In addition, multiphase volume flow rates for the constituents are obtained by velocity profile integration assuming vertical phase stratification in an approximation.
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 80 126 - 138 0894-1777 2017/01 [Refereed][Not invited]
     
    This paper presents an experimental study of the influence of wall surface wettability on the behavior of hydrogen microbubbles rising along a nearly vertical wall. Multiple optical diagnostics, including particle tracking velocimetry, have been employed for the study. The microbubble behavior observed along three different kinds of wall surfaces (hydrophobic, hydrophilic, and super-hydrophilic) was characterized by the microbubble-wall attachment, bubble size distribution, bubble coalescence, and microbubble layer formation. Microbubbles rising along the wall with poor wettability soon attach to the wall and grow to millimeters in size as a result of bubble coalescence. Such millimeter-sized bubbles detach from the wall because of their increased buoyancy, and eventually enhance transverse diffusion of microbubbles, which is known as the sweep-out effect. In contrast, in the case of very good wettability, almost no microbubbles attach to the wall and smoothly form a thin microbubble layer in the wall proximity. The observed phenomena contradict our intuitive expectation of the effect of surface wettability on gas bubbles, and hence may be regarded as a feature of microbubbles that distinguishes them from large bubbles. (C) 2016 Elsevier Inc. All rights reserved.
  • Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 27 (12) 0957-0233 2016/12 [Not refereed][Invited]
  • Hyun Jin Park, Yoshihiko Oishi, Yuji Tasaka, Yuichi Murai
    EXPERIMENTS IN FLUIDS 57 (12) 0723-4864 2016/12 [Refereed][Not invited]
     
    The injection of bubbles into a turbulent boundary layer can reduce the skin friction of a wall. Conventionally, the drag reduction rate is evaluated using time-averaged quantities of the mean gas flow rate or mean void fraction. Actually, as bubbles are subject to strong shear stresses near the wall, void waves and local bubble clusters appear. For pipe and channel flows, such wavelike behavior of the dispersed phase has been investigated intensely as an internal two-phase flow problem. We investigate how this wavy structure forms within the boundary layer as an external spatially developing two-phase flow along a horizontal flat plate. We describe how our model ship is designed to meet that purpose and report bubble-traveling behavior that accompanies unexpectedly strong wavy oscillations in the streamwise direction. A theoretical explanation based on a simplified two-fluid model is given to support this experimental fact, which suggests that void waves naturally stand out when drag reduction is enhanced through the local spatial gradient of the void fraction.
  • Tomoaki Takeuchi, Jumpei Ohkubo, Norio Yonezawa, Yoshihiko Oishi, Ichiro Kumagai, Yuji Tasaka, Yuichi Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 87 45 - 53 0301-9322 2016/12 [Refereed][Not invited]
     
    Internal gas velocity fluctuations and their effects on the mist diffusion process were examined in a long horizontal pipe to understand oil mist transportation, particularly in the laminar-to-turbulent flow transition region. Three hot-wire anemometers and aerosol concentration monitors were used to deduce these effects as the two-phase mist flow gradually developed in the stream-wise direction. We found significant axial mist diffusion at Reynolds numbers (Re) < 1000 because of passive scalar transport by Poiseuille flow. However, this diffusion was restricted by the non-zero inertia of the mist at a Stokes number, 0(10(-5)), relying on the Brownian motion of the mist. At Re > 2400, a sharp mist waveform was maintained by a turbulent flow with active radial mixing. New data were obtained within the range of 1000 < Re < 2400, which cannot be explained by interpolation between the above-mentioned two states. The mist concentration displays multiple temporal peaks at Re < 2000 owing to perturbations of localized turbulence as well as radial anisotropy as being conveyed more than 2000-diameters in distance. This behavior is caused by intermittent disturbances induced by the pipe wall roughness, which sharply distorts the wall-aligned laminar mist layer left by parabolic axial stretching of local laminar flow. (C) 2016 Elsevier Ltd. All rights reserved.
  • Jumpei Ohkubo, Yuji Tasaka, Hyun Jin Park, Yuichi Murai
    JOURNAL OF VISUALIZATION 19 (4) 643 - 651 1343-8875 2016/11 [Refereed][Not invited]
     
    A novel visualization technique was proposed to extract the three-dimensional vortex structure of a turbulent puff, which is a local turbulence event that is observed in pipe flows at relatively low Reynolds numbers. The technique is based on multi-color illumination of microscopic flakes that are suspended in the flow, which makes structural visualization more informative than conventional monochrome approaches. A special optical arrangement of two laser sheets, colored green and blue, was established for the circular pipe. Based on an image analysis sequence, the internal structure of the puff is reconstructed as a cross-sectional temporal 3D image consisting of voxels with unicolor degrees between green and blue, where an individual single vortex is extracted as a pair of two-color stripes. This allows quantification of the azimuthal wavenumber of the vortical structure that characterizes the puff. The wavenumber results agreed well with the results of previous studies, thus supporting the applicability of the proposed visualization technique..
  • Instability provoked by ascending bubbles in a horizontal liquid layer
    K. Nakamura, H. N. Yoshikawa, Y. Tasaka, Y. Murai
    Proceedings of annual meeting of Japan Society of Fluid Mechanics 2016/09 [Refereed][Not invited]
  • Quantitative evaluation of rheological properties for complex fluids using ultrasonic spinning rheometry
    Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 10) 2016/09 [Refereed][Not invited]
  • Takahiro Nakashima, Takahisa Shiratori, Yuichi Murai, Yuji Tasaka, Yasushi Takeda, Eric J. Windhab
    FLOW MEASUREMENT AND INSTRUMENTATION 48 97 - 103 0955-5986 2016/04 [Refereed][Not invited]
     
    Ultrasound velocity profiling was applied to viscoelastic flow induced around a moving permeable disk. There were two objectives to this measurement. The first was to find technical advantages and restrictions when applying ultrasonic Doppler velocimetry to a viscoelastic liquid. This issue has not been clarified even though ultrasonic pulses may interact with an elastic medium in the monitoring of the Doppler shift frequency. The second objective was to determine the fluid physics of a viscoelastic liquid around a permeable object, which will help in designing mixing process for materials subject to strong rheological resistance. In this paper, we report a representative response of a viscoelastic liquid in terms of its spatiotemporal velocity distribution. The response highlighted is cyclic lateral waves that form behind the disk, which were hardly detectable by particle image velocimetry. We discuss multiple reasons for this phenomenon considering not only fluid properties but also the measurement principle of ultrasound velocity profiling as applied to viscoelastic liquid. (C) 2015 Elsevier Ltd. All rights reserved.
  • Takahisa Shiratori, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 71 1 - 13 0894-1777 2016/02 [Refereed][Not invited]
     
    A method to characterize viscoelastic fluids in transient shear is proposed based on spatiotemporal flow velocimetry. Particle tracking velocimetry and ultrasound velocity profiling are functionally applied to obtain shear rate and shear strain of a fluid within a Couette system. The ratio of the cylinder radii is set large differently from ordinary Couette systems so that shear stress and shear strain in their designed ranges are available without changing the rotational speed. Simultaneously performing a torque measurement of the rotating cylinder with flow velocimetry, the spatiotemporal fluid response is converted into a triadic relation among shear rate, shear strain, and shear stress. The relationship is graphically represented as a "flow surface" in the three-dimensional parameter space. For an aqueous polyacrylamide solution, the elementary features, such as yield stress, shear wave, and shear-thinning trend, of the viscoelastic fluid reflected in the flow surface are read off. Finally, the experimental flow surface is directly applied for momentum conservation equation to simulate the viscoelastic flow structure as a demonstration. (C) 2015 Elsevier Inc. All rights reserved.
  • SATO Shu, TASAKA Yuji, MURAI Yuichi
    The Proceedings of Conference of Hokkaido Branch 一般社団法人 日本機械学会 2016 61 - 62 2016
  • Shuji OTOMO, Susumu OSUKA, Yuji TASAKA, Yuichi MURAI, Petr DENISSENKO
    The Proceedings of Conference of Hokkaido Branch 2016.54 (0) 79 - 80 2016
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 26 (12) 0957-0233 2015/12 [Refereed][Not invited]
     
    The behavior of a bubbly two-phase flow in the vicinity of a wall affects heat, mass, and momentum transfer; therefore, there is great interest in developing a quantitative technique to monitor this behavior. Herein we propose a new method based on ultrasound echo signal processing that it feasible for industrial applications where the boundary layer is modified by traveling bubbles. By introducing time-resolved direct waveform analysis at 100 MHz, we have succeeded in the spatio-temporal detection of bubble surfaces at echographic profiling frequencies in the range of 15-20 kHz. Unlike conventional approaches, which use short pulses, a relatively long pulse length is applied to allow ultrasound Doppler velocimetry in the liquid phase. Examination of the horizontal bubbly two-phase turbulent channel flows demonstrated the feasibility of this method; spatio-temporal echography of moving bubble surfaces is successfully achieved as the bubbles travel on length scales smaller than the spatial ultrasonic pulse length near the wall. The applicable range of parameters (e.g. bubble size and shape, and flow speed) was determined by 3D numerical analysis of the wave equation and its application to bubbles flowing beneath a flat-bottom model ship.
  • Hyun Jin Park, Yuji Tasaka, Yoshihiko Oishi, Yuichi Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 75 12 - 25 0301-9322 2015/10 [Refereed][Not invited]
     
    To promote the efficiency of frictional drag reduction using bubbles, we designed a novel bubble control method that involves repetitive injection of bubbles rather than the conventional continuous bubble injection approach. Even if the mean void fraction of bubbles to be injected into the turbulent boundary layer is set to be low, repetitive bubble injection (RBI) maintains the frictional drag reduction by generating bubble swarms. The enhanced drag reduction mechanism and the effectiveness of the RBI approach are investigated by studying wall shear stress and the velocity vector field in the liquid phase when measured in a turbulent horizontal channel flow. The bubble swarms generated by RBI consist of bubbles of various sizes with leading large air films, which have high reproducibility. The leading air films, which are a result of the concentrated void fraction, maintain a high drag reduction effect by air lubrication and by suppression of Reynolds shear stress events in the turbulent vortical structures beneath the bubble swarm. The latter effect of RBI in particular plays a significant role at higher Reynolds numbers. Based on the combination of these effects, we confirmed that RBI provides an extra drag reduction effect when compared with continuous bubble injection. (C) 2015 Elsevier Ltd. All rights reserved.
  • Takahisa Shiratori, Yuji Tasaka, Yoshihiko Oishi, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 26 (8) 0957-0233 2015/08 [Refereed][Not invited]
     
    We propose a new rheometry for characterizing the rheological properties of fluids. The technique produces flow curves, which represent the relationship between the fluid shear rate and shear stress. Flow curves are obtained by measuring the circumferential velocity distribution of tested fluids in a circular Couette system, using an ultrasonic velocity profiling technique. By adopting a widened gap of concentric cylinders, a designed range of the shear rate is obtained so that velocity profile measurement along a single line directly acquires flow curves. To reduce the effect of ultrasonic noise on resultant flow curves, several fitting functions and variable transforms are examined to best approximate the velocity profile without introducing a priori rheological models. Silicone oil, polyacrylamide solution, and yogurt were used to evaluate the applicability of this technique. These substances are purposely targeted as examples of Newtonian fluids, shear thinning fluids, and opaque fluids with unknown rheological properties, respectively. We find that fourth-order Chebyshev polynomials provide the most accurate representation of flow curves in the context of model-free rheometry enabled by ultrasonic velocity profiling.
  • Yuichi Murai, Takahisa Shiratori, Ichiro Kumagai, Patrick A. Ruehs, Peter Fischer
    FLOW MEASUREMENT AND INSTRUMENTATION 41 121 - 128 0955-5986 2015/03 [Refereed][Not invited]
     
    An experimental method for measuring the effective viscosity of two dimensional dispersion systems is proposed. The method is based on interfacial rheology, which was originally developed to investigate surface active adsorption layers such as protein film formed at liquid-liquid interfaces. Bubbles or rigid particles at around 50% of volume fraction in liquid are positioned in the gap between a rotating disk and a stationary cylindrical container. With this configuration, shear-rate dependent effective viscosities of bubble and particle layers were investigated. Steep shear-thinning property is observed for spherical bubble systems in the shear rate regime from 10(-1) to 10(2) s(-1). This is explained by topological transition from regular to random arrangement of the bubbles at the interface. For rigid particle systems, the viscosity starts from high value due to solid contact friction, then decreases sharply due to fluidization process until inter-particle collision lead to an increase of the viscosity. (C) 2014 Elsevier Ltd. All rights reserved.
  • Yuichi Murai, Takahisa Shiratori, Ichiro Kumagai, Patrick A. Ruehs, Peter Fischer
    FLOW MEASUREMENT AND INSTRUMENTATION 41 121 - 128 0955-5986 2015/03 [Refereed][Not invited]
     
    An experimental method for measuring the effective viscosity of two dimensional dispersion systems is proposed. The method is based on interfacial rheology, which was originally developed to investigate surface active adsorption layers such as protein film formed at liquid-liquid interfaces. Bubbles or rigid particles at around 50% of volume fraction in liquid are positioned in the gap between a rotating disk and a stationary cylindrical container. With this configuration, shear-rate dependent effective viscosities of bubble and particle layers were investigated. Steep shear-thinning property is observed for spherical bubble systems in the shear rate regime from 10(-1) to 10(2) s(-1). This is explained by topological transition from regular to random arrangement of the bubbles at the interface. For rigid particle systems, the viscosity starts from high value due to solid contact friction, then decreases sharply due to fluidization process until inter-particle collision lead to an increase of the viscosity. (C) 2014 Elsevier Ltd. All rights reserved.
  • Ichiro Kumagai, Yoshiaki Takahashi, Yuichi Murai
    OCEAN ENGINEERING 95 183 - 194 0029-8018 2015/02 [Refereed][Not invited]
     
    We have developed a new power-saving device to reduce the drag of a ship's hull using small bubbles. The device reduces the energy required for bubble generation. The device, which consists of angled hydrofoils with air introducers, uses the low-pressure region produced above the hydrofoil as the ship moves forward to drive atmospheric air into the water. We describe the device principles obtained from simple fluid dynamic theory, and, through experiments performed in a small towing tank, show the fundamental air entrainment and bubble generation processes for the flow behavior around a hydrofoil beneath a free surface. We also present a semi-empirical scaling process for practical application to full-size ships to estimate the net drag reduction achieved by this device. Finally, the results of a series of full-scale tests are reported and show that, with correct operation, our device can produce a net power saving of 5-15% for ships. (C) 2014 The Authors. Published by Elsevier Ltd.
  • Y. Tasaka, T. Kimura, Y. Murai
    EXPERIMENTS IN FLUIDS 56 (1) 0723-4864 2015/01 [Refereed][Not invited]
     
    We have proposed a novel methodology using ultrasonic velocity profiling to estimate the effective viscosity of bubble suspensions that are accompanied by non-equilibrium bubble deformations in periodic shear flows. The methodology was termed "ultrasonic spinning rheometry" and validated on measurement of the effective viscosity of particle suspensions that has a semi-empirical formula giving good estimation of the actual viscosity. The results indicated that the proposed technique is valid for particle volume fractions below 3.0 %. Applying this to bubble suspensions suggested that the effective value of temporal variations in the capillary number, Carms, is an important indicator to distinguish regimes in estimating the effective viscosity: Unsteady flows having larger Carms number than the critical capillary number for the deformation of bubbles are categorized into Regime 2 that includes both highly unsteady conditions and large steady deformation of bubbles.
  • Atsuhide Kitagawa, Yuichi Murai
    CHEMICAL ENGINEERING SCIENCE 116 694 - 703 0009-2509 2014/09 [Refereed][Not invited]
     
    Based on the experimental finding that microbubble swarms dramatically promote heat transfer from a vertical heated wall, despite their potentially adiabatic nature, tests of microbubble fluid mechanics in the isothermal state are performed to clarify the unique motion characteristics of microbubble swarms. At constant bubble flow rate, the microbubble swarm shows a significant pulsatory rise along a vertical flat wall, particularly for small bubbles. Particle tracking velocimetry applied to the microbubbles shows that a two-way interaction between the microbubbles and the liquid flow self-excites the pulsation during their co-current rise. The sequence consists of the following processes: (i) increase in the bubble number density close to the wall as a result of the liquid velocity gradient driven by the microbubbles themselves; (ii) wave generation inside the microbubble swarm to induce the pulsatory rise of the swarm; and (iii) amplification of the waves, which results in void-bursting motion in the final stage. (C) 2014 Elsevier Ltd. All rights reserved.
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Yoshihiko Oishi
    CHEMICAL ENGINEERING SCIENCE 116 486 - 496 0009-2509 2014/09 [Refereed][Not invited]
     
    Bubbles injected into a wall turbulent boundary layer can modify heat, mass, and momentum transfers of the wall. One factor responsible for the phenomenon is alternation of the vortical flow structures near the wall. To demonstrate this graphically, we directly visualized the interaction between the vortical flow structures and a bubble swarm composed of bubbles with various sizes, by means of two-color laser-sheet illumination of the wall turbulence with a dilute suspension of flakes. Image processing realized quantitative characterization of interaction events in the buffer and logarithmic layers, referring to multiple measured quantities such as the relative advection velocity between bubbles and turbulence, spacing of vortices both in streamwise and spanwise directions, persisting lengths of vortices in both directions, and statistical inclination angles of the streamwise vortices. A particular finding from the present visualization is that the streamwise vortices in the buffer layer were swept by the bubble swarm but brought to the backside of the swarm to survive until the swarm passed by. (C) 2014 Elsevier Ltd. All rights reserved.
  • Yuichi Murai
    EXPERIMENTS IN FLUIDS 55 (7) 0723-4864 2014/07 [Refereed][Invited]
     
    The injection of gas bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. This explains why a number of different void-drag reduction relationships have been reported to date, while early works pursued a simple universal mechanism. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. Each regime has inherent physics of bubbly liquid, highlighted by keywords such as bubbly mixture rheology, the spectral response of bubbles in turbulence, buoyancy-dominated bubble behavior, and gas cavity breakup. Among the regimes, bubbles in some selected situations lose the drag reduction effect owing to extra momentum transfer promoted by their active motions. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. This article reviews the roles of bubbles in drag reduction, which have been revealed from fundamental studies of simplified flow geometries and from development of measurement techniques that resolve the inner layer structure of bubble-mixed turbulent boundary layers.
  • Transition of flow structure at marginal conditions in internally heated convection with background rotation
    Y.YAMAGUCHI, Y.TASAKA, Y.OISHI, Y.MURAI, T.YANAGISAWA
    Asia Oceania Geosciences Society 2014 USB  2014/07 [Not refereed][Not invited]
  • Investigation of cell patterns on a rotating convection by ultrasonic velocity profile measurements
    K.FUJITA, Y.TASAKA, Y.OISHI, Y.MURAI, T.YANAGISAWA
    Asia Oceania Geosciences Society 2014 USB  2014/07 [Not refereed][Not invited]
  • Visualization of bubble motion in a horizontal channel using different surface conditions
    A.KITAGAWA, M.GOTO, Y.KIMURA, Y.OISHI, Y.MURAI
    16th International Symposium on Flow Visualization 2014 Okinawa ISFV16-1060 1 - 10 2014/06 [Refereed][Not invited]
  • Measurement of Bubble cluster formed in a horizontal Turbulent channel flow
    Y.OISHI, T.TASAKA, Y.MURAI, Y.TOHGE
    16th International Symposium on Flow Visualization 2014 Okinawa ISFV16-1279 1 - 11 2014/06 [Refereed][Not invited]
  • Yoshihiko Oishi, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 55 128 - 139 0894-1777 2014/05 [Refereed][Not invited]
     
    Flow field modified by a single large bubble in a horizontal wall turbulent boundary layer is measured by particle tracking velocimetry. We focus on intermediate bubble size being comparable to the thickness of boundary layer to find out the events altering the original turbulent shear stress field. The results are all presented by quantities relative to single phase flow on Lagrangian grid system that moves with the bubble. The measurement results reveal bubble-produced secondary flow around itself, which involves twin roll vortices, separation on the bubble surface, and strong sweeping flow. For a small and nearly spherical bubble, the sweeping flow is provided strongly to enhance the turbulent momentum exchange while negative exchange is detected for a large flat bubble. This effective length approximately corresponds to the size of the bubble. (C) 2014 Elsevier Inc. All rights reserved.
  • KITAGAWA Atsuhide, OKU Tatsuaki, OZATO Takuya, MURAI Yuichi
    TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series A The Japan Society of Mechanical Engineers 80 (811) TEP0044 - TEP0044 2187-9761 2014 
    This paper presents the temperature and velocity measurements to clarify effects of inclination angle of a heated plate φ on natural-convection heat transfer enhancement by millimeter bubbles. In the range 0≤φ≤30˚, the heat transfer coefficient with bubble injection is much higher than that without injection, and the ratio of the heat transfer coefficient with bubble injection to that without injection (heat transfer coefficient ratio) ranges from 3.0 to 5.0. This is due to enhancement of both the transport of the warm liquid toward the downstream region and the mixing of warm liquid and cool liquid. The former results from the bubble-induced liquid entrainment, and the latter is mainly due to the increase in the liquid velocity fluctuation induced by a combination of the bubble motion and the vortex shedding from the bubble interface. Moreover, the significant bubble-induced liquid entrainment and the unsteady vortex occur near the heated wall at higher inclination angle of the heated plate. Hence, the heat transfer coefficient ratio increases with increasing inclination angle of the heated plate.
  • Norio Yonezawa, Yoshihiko Oishi, Yuji Tasaka, Yuichi Murai
    8TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1592 177 - 186 0094-243X 2014 [Refereed][Not invited]
     
    As small solid particles are mixed in gas flow in a horizontal pipe, the particles are sometimes long suspended downstream due to dynamic interaction between two phases in turbulent states. Dunes of such particles are naturally formed at the bottom of the pipe in case of heavy flow rate of particles, and the dunes rather help the particles with suspension further downstream. In this study, PTV has been applied for measurement of such particles floating inside a horizontal pipe behind a synthetic dune. Time-resolved PTV analysis of the particle behavior in the section perpendicular to the mainstream has revealed that long-suspended particles keep floating with fountain like convection pattern inside the circular pipe, which consists of ascending flow at the center of the pipe, bouncing flow at the wall, and downwash at the oblique part. The present paper shows their dynamic statistics of the particle behavior for the cross-sectional distributions of concentration, velocity vector, and acceleration vector.
  • Ichiro Kumagai, Yuichi Murai, Yoshiaki Takahashi, Haruki Sakamaki, Takahiro Tsukahara, Tsubasa Ozaki, Yuji Tasaka, Yoshihiko Oishi
    8TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1592 322 - 328 0094-243X 2014 [Refereed][Not invited]
     
    We have invented two types of hydrofoil bubble generator for drag reduction of ship that can reduce the energy for air bubble generation on the ship hull. Their fundamental process of air entrainment and subsequent bubble generation by the hydrofoil facility are described by a simple fluid dynamic model. We experimentally determined the critical velocity of the bubble generation and the relationship between air volume flow rate and the hydrofoil velocity. The magnitude of the negative pressure produced above the hydrofoil, which is a driving force of the air entrainment, depends on the shape of the hydrofoil, gap ratio (normalized depth of the hydrofoil), Reynolds number, Froude number, and angle of attack. Recent applications of the drag-reduction technology with air bubbles to a ship save about 10%-15% of the total energy consumption of the ship. The device works as a self-priming pump when the draft of the ship is shallow (< similar to 5 m) as predicted by the theory. For ships of deeper draft, the device needs the assistance of an air compressor. Because the magnitude of the negative pressure above the hydrofoil depends on the flow condition around the hydrofoil, proper operation of compressors is necessary. We also show experimental results on optimization of hydrofoils to enhance the hydrofoil performance of air entrainment and air bubble generation.
  • Atsuhide Kitagawa, Takuya Mimura, Masaaki Ishikawa, Yuichi Murai
    JOURNAL OF VISUALIZATION 16 (4) 313 - 321 1343-8875 2013/11 [Refereed][Not invited]
     
    We use visualization to investigate the structure of the counter-current convection induced by microbubbles and small particles. In particular, we study the effect of small particles with different specific gravities on the gas-phase flow. In our experiments, microbubbles are injected into stationary liquid from a bubble generator that is set at the bottom of a vertical channel, and small particles are injected from a particle injector that is set at the top of the channel. The mean kinetic energy of the gas-phase is significantly lower in the flow with microbubbles and small particles than in the flow with only microbubbles. This results from significant suppression of the interaction of bubble plumes by the small particles. Moreover, the mean kinetic energy of the gas-phase in the flow with microbubbles and small particles is strongly dependent on the specific gravity of the small particles.
  • Takahisa Shiratori, Yuji Tasaka, Yuichi Murai, Yasushi Takeda
    JOURNAL OF VISUALIZATION 16 (4) 275 - 286 1343-8875 2013/11 [Refereed][Not invited]
     
    In the field of rheology, properties of non-Newtonian fluids have been traditionally represented on graphs such as viscosity curves. In this paper, we propose a visualizer to express the fluid properties as visualized fluid motions in a rotating cylinder. To highlight different fluid motions, three patterns of rotation were given to the cylinder: rapid start of constant rotation (spin-up), rapid stop from constant rotation (spin-down), and periodic rotation. Relationships between fluid motion and fluid properties are discussed by comparing velocity profiles for three fluids: silicone oil, yogurt, and a polyacrylamide (PAA) solution. Ultrasonic velocity profiler (UVP) was used to obtain spatio-temporal velocity maps. The velocity maps reflect essential rheological properties, such as shear thinning, yield stress, and elasticity. Two additional display modes are proposed to explore fluid motions due to viscoelasticity of the PAA solution and yogurt: a grid deformation field and a shear rate field. These two visualizations can provide intuitive understanding of viscoelasticity because deformation and shear rate determine elastic and viscous stresses, respectively. In spin-down tests, the recovery of deformed grids, which is caused by elasticity, can be explicitly observed. Further, the shear rate distributions indicate that kinetic energy of the fluid dissipates near the lateral wall right after the wall stops rotating. In short, these two quantity fields visualize energy conversion among kinetic, elastic, and thermal energy; such energy conversions are characteristic of viscoelastic fluids.
  • Yuichi Murai, Jozef H. A. Vlaskamp, Yuichi Nambu, Takahiro Yoshimoto, Mark A. Brend, Petr Denissenko, Peter J. Thomas
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 51 342 - 353 0894-1777 2013/11 [Refereed][Not invited]
     
    A new simple optical method for visualizing flow structures generated in a rotating flow is presented. The method consists of planar PTV with sheet illumination slightly offset to the rotation axis and a geometric reconstruction of velocity vector field under the assumption of azimuthal periodicity. Two types of columnar flows intrinsically associated with rotating flows are investigated with the method. The two types of flow are a local columnar wake induced behind a moving sphere, and an asymmetrically precessing Taylor Column created below a spinning disk. By means of this new technique we obtain the first quantitative visualization of the columnar wake and the three-dimensional structure of the Taylor Column. (C) 2013 Elsevier Inc. All rights reserved.
  • Time-Resolved Measurement of Frictional Drag Reduction by Bubbles with Void Waves
    Y.OISHI, T.WATAMURA, Y.TASAKA, Y.MURAI
    The 12th International Symposium on Fluid Control, Measurement and Visualization (FLCOME2013) OS8-03-2 USB  2013/11 [Refereed][Not invited]
  • H.SAKAMAKI, I.KUMAGAI, Y.OISHI, Y.TASAKA, Y. MURAI
    4th International Conference on Jets, Wakes and Separated Flows, (ICJWSF-2013) 一般社団法人日本機械学会 2013 (4) ICJWSF2013-1051, pp.1-6 (CD-RO - 1"-"1051-6" 2013/09 [Refereed][Not invited]
     
    With the aim of optimizing performance of a hydrofoil bubble introducer for drag reduction of ship, the flows and free surface deformation around a hydrofoil were investigated experimentally in a wide range of Reynolds number, Froude number, gap ratio (normalized depth), and angle of attack. Image processing for the obtained images of flows and free surface elucidated the key factor of the free surface deformation and the conditions of flow separation on hydrofoils. Flow fields around the hydrofoil determined by PTV represent influence of the free surface with large deformation on the flow field quantitatively. These results provide fruitful information for the optimization of this hydrofoil facility.
  • Structure of a Vortex Ring Impacting on a Solid Boundary with Background Rotation
    Y.AIKAWA, Y.NAMBU, Y.OISHI, Y.TASAKA, Y.MURAI, P.J.THOMAS
    4th International Conference on Jets, Wakes and Separated Flows, (ICJWSF-2013) ICJWSF2013-1062, pp.1-6 (CD-RO  2013/09 [Refereed][Not invited]
  • Atsuhide Kitagawa, Yuichi Murai
    CHEMICAL ENGINEERING SCIENCE 99 215 - 224 0009-2509 2013/08 [Refereed][Not invited]
     
    The effects of microbubble injection on natural convection heat transfer from a vertical heated plate in water are experimentally investigated. Thermocouples are used to measure the temperature, and an image processing technique is used to obtain the bubble diameter, bubble velocity, and bubble layer thickness. Tap water is used as the working liquid, and hydrogen bubbles generated by water electrolysis are used as the microbubbles. At a constant wall heat flux, microbubble injection significantly increases the heat transfer coefficient in both the laminar and transition regions. The ratio of the heat transfer coefficient with bubble injection to that without injection is 1.6-2.0 in the laminar region and 1.5-2.0 in the transition region. The enhancement of heat transfer in the laminar region results from both the forced convection and mixing effects. In contrast, the enhancement of heat transfer in the transition region arises mainly because microbubble injection accelerates the transition to turbulence. (C) 2013 Elsevier Ltd. All rights reserved.
  • Miyuki Yamada, Yuichi Murai, Ichiro Kumagai
    JOURNAL OF VISUALIZATION 16 (3) 247 - 257 1343-8875 2013/08 [Refereed][Not invited]
     
    A new method for visualization of stories in literary works was explored. Our story visualization method consists of two parts: keyword-based statistical analysis for multiple themes and imagery expression of the results for visual understanding. In this study, we focused on novels as the targets, and discussed ways in which complex structures can be simultaneously visualized using multiple themes. The method was applied for the comparison of Charles Dickens' novels with Shakespeare's plays in order to identify any existing evidence concerning literal interest created by the overlapping of multiple scenarios in a single story. We also applied the method to non-literary documents such as newspaper articles, and showed that these documents contain simple statistic patterns regarding a given theme, which contrasts with the case involving novels that include the dynamic fluctuation of individual story elements.
  • Color Tomographic PIV Improved by Removal of Color Contamination
    Y.MURAI, T.YUMOTO, Y.OISHI, Y.TASAKA
    The 10th International Symposium on Particle Image Velocimetry PIV2013 USB, pp.1-8  2013/07 [Refereed][Not invited]
  • Dynamic 1D-2C PTV for boundary layer measurement
    Y.OISHI, Y.MURAI
    The 10th International Symposium on Particle Image Velocimetry PIV2013 P19, USB, p.187  2013/07 [Refereed][Not invited]
  • T. Watamura, Y. Tasaka, Y. Murai
    PHYSICS OF FLUIDS 25 (5) 1070-6631 2013/05 [Refereed][Not invited]
     
    The effect of the presence of microbubbles on a flow state is experimentally investigated in a Taylor-Couette flow with azimuthal waves, in order to examine the interaction mechanism of bubbles and flows that result in drag reduction. The average diameter of the bubbles is 60 mu m, which is smaller than the Kolmogorov length scale, and the maximum void fraction is 1.2x10(-4) at the maximum case. The modifications of the fluid properties, bulk density, effective viscosity, and the extra energy input caused by the addition of microbubbles are expected to have a small effect on modifying flow states. The power of the basic wave propagating in the azimuthal direction is enhanced; its modulation, however, is decreased by adding microbubbles in the flow regime corresponding to modulated Taylor vortex flow. Moreover, the gradient of the azimuthal velocity near the walls, source of the wall shear stress, decreases by 10%. The modified velocity distribution by adding microbubbles is comparable to that obtained with a 20% lower Reynolds number. Microbubbles in the coherent structure of the wavy Taylor vortices are visualized and exhibit a preferential distribution and motion at the crests and troughs of the waviness. The roles of the inhomogeneously distributed microbubbles in wavy vortical structures are discussed in view of our findings. (C) 2013 AIP Publishing LLC.
  • Tomoaki Watamura, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 47 68 - 80 0894-1777 2013/05 [Refereed][Not invited]
     
    Color-based three-dimensional (3D) Particle Tracking Velocimetry (PTV) using a single camera and an liquid crystal display (LCD) projector, which can measure the out-of-plane velocity component from particle color information, is improved for practical use in 3D velocimetry without losing the original simplicity on the optical configuration of planner 2D PTV. To minimize the uncertainties in identifying the representative color of particles, we propose new color identifying algorithms that average hue in polar rather than linear coordinates. The proposed algorithm, a saturation-weighted-averaged hue in polar coordinates, yields smaller standard deviations than conventional algorithms: 1.4% in hue and 2.0% in position detection. Use of a multiple color-cycle gradation light for volumetric illumination of the fluid layers also improves the resolution of the position and velocity measurements in the depth direction. The proposed measurement technique can display the flow patterns of an axisymmetric rotating flow from instantaneous 3D-3C velocity vector fields, as well as the vortex structure of an unsteady flow represented as iso-surfaces of enstrophy density. (C) 2013 Elsevier Inc. All rights reserved.
  • Clustering of Air Bubbles Injected in Horizontal Channel Flow
    Y.OISHI, Y.TOHGE, Y.TASAKA, Y.MURAI
    International Conference on Multiphase Flow 2013 ICMF2013-584 USB, pp.1-6  2013/05 [Refereed][Not invited]
  • Effects of flaps and vortex generators on air entrainment by a hydrofoil bubble generator for drag reduction of ships
    KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji, OISHI Yoshihiko, SAKAMAKI Haruki, YAMAUCHI Hideaki, ISAHIKAWA Yutaro, EGASHIRA Ryu
    Proceedings of International Conference on Multiphase Flow 2013 (ICMF2013) #594 2013/05 [Refereed][Not invited]
  • Xiaoshu Cai, Zhiyao Huang, Feng Dong, Yuichi Murai
    PARTICUOLOGY 11 (2) 134 - 134 1674-2001 2013/04
  • T.Watamura, Y.Tasaka, Y.Murai
    Theoretical and Applied Mechanics Japan 61 2013/02 [Refereed][Not invited]
  • Kosuke Sakurai, Yuji Tasaka, Yuichi Murai
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 79 (797) 1 - 11 0387-5016 2013 [Refereed][Not invited]
     
    A new approach to deduce the effective viscosity of bubbly liquid with considering non-equilibrium bubble deformations in transient shear flows was proposed. Simultaneous measurement of the bubble shape and the spatio-temporal velocity distribution clarified that bubble deformation has delay from a variation of the local Capillary number under a transient process of flows from a stationary state to a rigid body rotation (spin-up) in a rotating cylinder. Relative viscosity of the bubbly liquid against the single phase condition estimated by the proposed method shows 60 % increase as the maximum. Such large increase of the effective viscosity cannot be introduced by mixture of spherical bubbles and bubbles with equilibrium deformations, and thus the non-equilibrium bubble deformations take a primary role on the modification of the effective viscosity in unsteady shear flows. © 2013 The Japan Society of Mechanical Engineers.
  • TASAKA Yuji, MURAI Yuichi
    Transactions of the Japan Society of Mechanical Engineers Series C The Japan Society of Mechanical Engineers 79 (798) 227 - 227 0387-5016 2013 
    式にフォントが乱れているものがございましたので，修正させていただきます．
  • Atsuhide Kitagawa, Takuya Ozato, Yuichi Murai
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 79 (800) 701 - 711 0387-5016 2013 [Refereed][Not invited]
     
    This paper presents an experimental investigation of motion characteristics of microbubbles rising close to a vertical plane wall. The study focuses on how microbubble behaviors change with the bubble diameter and along the wall for a constant bubble flow rate. Tap water is used as the working fluid, and hydrogen microbubbles are generated by water electrolysis. A particle tracking velocimetry technique is used to precisely measure the microbubble velocity, with which we found that the mean rise velocity of microbubbles is much faster than theoretically estimated rise velocity of single microbubble in stationary water. The mean bubble rise velocity increases with the bubble diameter and decreases in the downstream direction, and both are related to the balance between accumulation and diffusion of spatial buoyancy distribution near the wall. In particular, in the case of small microbubbles, bubble clouds are generated close to the wall and show intermittent roll-up motion in the wall-perpendicular direction (void burst motion). We discussed on this motion with various waveforms of the bubble rise velocity and bubble-bubble distance. ©2013 The Japan Society of Mechanical Engineers.
  • マイクロバブルの導入による水平混合層の局所乱流スペクトル変形
    渡村友昭, 田坂裕司, 村井祐一
    日本混相流学会論文集 27 (5) 521 - 530 2013 [Refereed][Not invited]
  • KITAURA Hidekazu, MURAI Yuichi, TASAKA Yuji, KUMAGAI Ichiro, KINO Seiji
    Transactions of the Japan Society of Mechanical Engineers Series C The Japan Society of Mechanical Engineers 79 (801) 966 - 979 0387-5016 2013 [Refereed][Not invited]
     
    Fluid dynamic process of density destratification enabled by a bubble plume is investigated. General parametric dependence to global mixing is studied with numerical simulation coded by number density model of bubbly flow and then multiple experiments using dye visualization and ultrasonic velocity profiling (UVP) are carried out to find out the spatiotemporal structure of the two-phase flow emerging during destratification. The results show that intermittent convection driven in the near field of the bubble plume plays the primary role of the destratification. The intermittency is triggered by interaction between the near-field turbulence and the far-field wavy motion of bubble plume, which is clearly shown by the recurrence map and the power spectra of the velocity fluctuation measured by UVP.
  • シリコンオイルによる水平チャネル内気泡流の摩擦抵抗特性（第2報 壁面せん断応力の時間変動解析）
    大石義彦, 村井祐一, 田坂裕司
    混相流 28 (1) 81 - 89 2013 [Refereed][Not invited]
  • シリコンオイルによる水平チャネル内気泡流の摩擦抵抗特性（第1報 摩擦抵抗計測とゲイン評価）
    大石義彦, 村井祐一, 田坂裕司
    混相流 28 (1) 71 - 80 2013 [Refereed][Not invited]
  • 熊谷 一郎, 大薮 剛志, 田坂 裕司, 村井 祐一
    混相流 25 (5) 399 - 406 0914-2843 2012/08 [Refereed][Not invited]
  • MURAI Yuichi, TASAKA Yuji, OISHI Yoshihiko
    Transactions of Visualization Society of Japan The Visualization Society of Japan 32 (126) 19 - 22 0916-4731 2012/07/01 
    A variety of gas-liquid two-phase flow patterns observed in a horizontal channel is introduced in the paper. The motivation of the experiment originates from drag reduction technique development for marine vessels in sea water, which requires physical mechanism toward practical utilization. The authors' group carried out high-speed air-water mixture visualization as well as low-speed silicone oil loop experiment so that what the figure of the gas-liquid interfaces imply when we discuss about the mechanism. The series of visualization showed multiple novel interpretation of the mechanism; spanwise clustering of bubbles takes place in laminar bubbly two-phase flow, streamwise striping of bubble distribution is formed in turbulent condition, and chained bubbles with large deformation appear at the intermediate conditions. The difference of the bubble clustering is understood to have a correlation to wall shear stress that has been reduced when clustering becomes strong.
  • Flow visualization around a hydrofoil close to a free surface
    I.Kumagai, T.Kushida, K.Oyabu, Y.Tasaka, Y.Murai
    Visualization of Mechanical Processes 3 (3-120) 1 - 7 2012/06 [Refereed][Not invited]
  • Ichiro Kumagai, Koji Oyabu, Takafumi Kushida, Yuichi Murai, Yuji Tasaka, Yoshiaki Takahashi
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 78 (787) 500 - 503 0387-5016 2012 [Refereed][Not invited]
     
    We have invented a new power-saving device for ship drag reduction using microbubbles in order to reduce CO 2 emissions from ships. The new device, which consists of angled hydrofoils with air introducers, has been installed on a coaster and helps achieving ∼10% net power saving. This device utilizes a low-pressure region produced above the hydrofoil as the ship moves forward, which drives atmospheric air into the water. Emissions can be reduced by about 87 million CO 2 ton/year if international shipping uses this new device, with 10% net-power reduction. We present the principal and optimization of this device on the basis of laboratory experiments on hydrofoils moving close to a free surface. In particular, we discuss free surface deformation and entrainment process using hydrofoils. © 2012 The Japan Society of Mechanical Engineers.
  • Atsuhide Kitagawa, Kazuaki Yamamoto, Yuichi Mural
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 78 (793) 1539 - 1549 0387-5016 2012 [Refereed][Not invited]
     
    This paper describes effects of microbubble injection on natural convection heat transfer from a vertical heated plate in water. Thermocouples are used for the temperature measurement and an image processing technique is used for obtaining the bubble diameter, the bubble velocity and the bubble layer thickness. The working fluid used is tap water. and li drogcn bubbles generated b electrolysis of the water are used as the inicrobubbles. For a constant bubble flow rate and a constant wall heat flux, in the laminar and transition regions. the heat transfer coefficient is significantly increased by the microbubble injection (The ratio of the heat transfer coefficient with bubble injection to that without injection is I .6-2.0 in both regions). The heat transfer enhancement in the laminar region results from both the forced-cons cction and mixing effects due to microbubbic injection. On the other hand, the heat transfer cnhaiemncnt in the transition region is iiiainlv affected b' acceleration of the transition to turbulence due to microbubblc injection. © 2012 The Japan Society of Mechanical Engineers.
  • Hideki Murakawa, Tatsuya Kawaguchi, Hironari Obayashi, Yuichi Murai, Yuji Tasaka
    Fluid Mechanics and its Applications 101 227 - 262 0926-5112 2012 [Refereed][Not invited]
     
    We have many demands to understand flow phenomena in many industrial applications. Detecting the gas-liquid interface is important when measuring velocities in two-phase flow or in an open channel. We want to obtain velocity distributions two dimensionally, also. To extend the applicability, many techniques utilizing the ultrasonic Doppler velocity profiler (UVP) have been recently developed. This chapter shows these extended techniques. Liquid and gas velocity distributions are obtained simultaneously using a multi-wave transducer are described in Sect. 7.1. Techniques detecting a gas-liquid interface depending on fluid interface relative to the ultrasonic wavelength are presented in Sect. 7.2. The UVP is utilized for measuring void fraction distributions in Sect. 7.3. Section 7.4 shows a technique measuring two-dimensional velocity components. A new approach for improving temporal resolution using the ultrasonic correlation method is presented in Sect. 7.5.
  • Yuichi Murai, Noriyuki Furuichi, Yasushi Takeda, Yuji Tasaka
    Fluid Mechanics and its Applications 101 71 - 103 0926-5112 2012 [Refereed][Not invited]
     
    On the basic of the ultrasonic principle made clear in Chaps. 1- flow velocity profiling can be realized if the Doppler method is applicable to the flow system. There are standard velocity fields, which are the most appropriate systems for examining the performance of ultrasonic velocity profiling (UVP) and training users in making UVP measurements. The standard velocity fields have a one-dimensional one-component velocity distribution, irrespective of whether they are steady or unsteady, such as in the case of flow in a rotating circular cylinder and laminar flow in a pipe. Measuring flow in such systems helps clarify the functions of UVP subject to diverse practical problems. Once velocity information is acquired, it is suitably adjusted in post-processing. Post-processing has two purposes: one is to improve the data quality in response to the inclusion of noise in velocity data, and the other is to derive statistical and other quantities.
  • Yuji Tasaka, Beat Birkhofer, Noriyuki Furuichi, Hiroshige Kikura, Hisato Minagawa, Yuichi Murai, Hideki Murakawa, Masaaki Motozawa, Samsun Nahar, Hironari Obayashi, Tatsuo Sawada, A. K. Jeelani Shaik, Yasushi Takeda, Kenichi Tezuka, Yoshiyuki Tsuji, Takatoshi Yanagisawa, Sanehiro Wada, Johan Wiklund, Erich J. Windhab
    Fluid Mechanics and its Applications 101 107 - 200 0926-5112 2012 [Refereed][Not invited]
     
    Because of the advantages of the ultrasonic velocity Doppler profiler (UVP), namely in spatiotemporal velocity field measurements and in its applicability for opaque liquids, UVP has a wide field of application in science and industry. The following chapter introduces carefully selected examples of applications covering relatively basic areas of application. The focus of the contents in this chapter is categorized into (1) studies of flow instability and transition (Sect. 5.1), (2) measurements and investigations of liquid metal flows (Sect. 5.2), (3) developments of new rheometry (Sect. 5.3), (4) determinations of rheological properties (Sect. 5.4), (5) studies of magnetic fluids (Sect. 5.5) and (6) gas-liquid two-phase flow (Sect. 5.6), (7) measurements of flowrate in turbidity flows (Sect. 5.7), and (8) -determinations of flows in a deforming tube for biomedical applications (Sect. 5.8). The measurement and post-processing techniques used in this chapter are described in detail in Chaps. 4 and 7, and, detailed explanations of these aspects are omitted in this chapter.
  • Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    7TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1428 0094-243X 2012 [Refereed][Not invited]
     
    Ultrasound pulse Doppler method is applied for componential volumetric flow rate measurement in multiphase pipe flow consisted of gas and liquid phases. The flowmetering is realized with integration of measured velocity profile over the cross section of the pipe within liquid phase. Spatio-temporal position of interface is detected also with the same ultrasound pulse, which further gives cross sectional void fraction. A series of experimental demonstration was shown by applying this principle of measurement to air-water two-phase flow in a horizontal tube of 40 mm in diameter, of which void fraction ranges from 0 to 90% at superficial velocity from 0 to 15 m/s. The measurement accuracy is verified with a volumetric type flowmeter. We also analyze the accuracy of area integration of liquid velocity distribution for many different patterns of ultrasound measurement lines assigned on the cross section of the tube. The present method is also identified to be pulsation sensor of flow rate that fluctuates with complex gas-liquid interface behavior.
  • Koji Oyabu, Ichiro Kumagai, Yuji Tasaka, Yuichi Murai
    7TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1428 0094-243X 2012 [Refereed][Not invited]
     
    We have conducted laboratory experiments on the flow past a circular cylinder moving beneath an air-water interface. The vortex street and the free surface profile are visualized for Reynolds number between 200 and 15000 and for Froude number between 0.01 and 3.2. For the lower Reynolds number (Re <= 3000), the vortex shedding from a circular cylinder is suppressed by the free surface at the small gap ratio for Re<1000. As a result, the vortex structure becomes smaller and the frequency of eddy shedding decreases. At the higher Reynolds number (>10000), the surface deformation becomes substantial in the downstream of the cylinder and intermittent bubble injection by wave breaking is observed. In order to investigate the relationship between the frequency of the vortex shedding and the free-surface wave behavior, Lagrangian Frame PIV measurement is conducted. From the results of Strouhal-Reynolds number relationship for gap ratios between 0.25 and 2.0, the period of the vortex shedding becomes long when the gap ratio is small.
  • Ichiro KUMAGAI, Takafumi KUSHIDA, Koji OYABU, Yuji TASAKA, Yuichi MURAI
    Visualization of Mechanical Process 1 (3) 10.1615 /VisMechProc.v1.i3.120  2012 [Refereed][Not invited]
  • MURAI Yuichi
    JAPANESE JOURNAL OF MULTIPHASE FLOW THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 25 (3) 237 - 244 0914-2843 2011/09/15 
    Particle image velocimetry and ultrasound velocity profiling have around 25 years in history from their first appearance on literature. The early type of their instruments measures flows only at very slow speed in simple spatial structure. The rapid advances in computing tip above silicon cycle escalated them onto the stage of wide applications from fundamental study in fluid mechanics to major experimental tool for designing, managing, and evaluating of thermo-fluid phenomena. Extension to multiphase flow in the last decade is making their big news both in science and engineering researches. This article reports on the current topics and technical problems in multiphase flow toward next generation.
  • Akinari Shigetomi, Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    RENEWABLE ENERGY 36 (2) 536 - 545 0960-1481 2011/02 [Refereed][Not invited]
     
    The use of a Savonius type of vertical axis wind turbine is expanding in urban environments as a result of its ability to withstand turbulence as well as its relatively quiet operation. In the past, single turbine performance has been investigated primarily for determining the optimum blade configuration. In contrast, combining multiple Savonius turbines in the horizontal plane produces extra power in particular configurations. This results from the interaction between the two flow fields around individual turbines. To understand quantitatively the interaction mechanism, we measured the flow field around two Savonius turbines in close configurations using particle image velocimetry. The phase-averaged flow fields with respect to the rotation angle of the turbines revealed two types of power-improvement interactions. One comes from the Magnus effect that bends the main stream behind the turbine to provide additional rotation of the downstream turbine. The other is obtained from the periodic coupling of local flow between the two turbines, which is associated with vortex shedding and cyclic pressure fluctuations. Use of this knowledge will assist the design of packaged installations of multiple Savonius turbines. (c) 2010 Elsevier Ltd. All rights reserved.
  • Ichiro Kumagai, Yuichi Murai, Kei Kurita
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 77 (784) 2236 - 2245 0387-5016 2011 [Refereed][Not invited]
     
    The dynamics of melt migration in partially molten media has long been of interest in physical systems. In order to understand the spatio-temporal patterns of fluid transport in partially molten materials, we explored laboratory experiments on the behavior of viscous flow through deformable porous media. Our experiments were carried out in a transparent rectangular tank (2 × 20 × 18 cm) filled with deformable gel beads (poly acrylamide). A viscous fluid (sugar syrup-water mixture) was injected from a nozzle or a slit placed at the top of the tank. The viscosity and the flow rate of the injected fluid were varied (0.1∼11 Pa.s 0.05∼0.33 ml/s). We identified three types of fluid flow in the experiments: (1) homogeneous permeable flow, (2) pulsating flow, and (3) localized continuous plume flow. The transition from the homogeneous permeable flow to the localized fluidized flow depends on injection flow rate, viscosity of the fluid, and deformation behaviors of the porous media. The second type of the flow has a characteristic period equivalent to the pulsation interval. This pulsating phenomenon within the gel mixture is excited by the fluid motion of the injected fluid and is controlled by a self-adjustable hydrodynamic valve composed of deformable gel beads. © 2011 The Japan Society of Mechanical Engineers.
  • マイクロバブルプーム群の浮上成長に関する定量的可視化実験
    日本機械学会論文集 B77 88 - 97 2011 [Refereed][Not invited]
  • KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji, NAKAMURA Naoya
    JFST The Japan Society of Mechanical Engineers 6 (6) 2152 - 2159 1880-5558 2011 [Refereed][Not invited]
     
    Wave breaking and air bubble generation by a 2-D cylinder moving beneath a free surface were experimentally investigated. Measurements of the free surface profile and visualization of the air bubbles yield the threshold and the regime diagrams of the bubble generation, which depend on the cross-sectional shape of the cylinder, Reynolds number, effective Froude number, normalized depth of the cylinder and angle of attack. As the Reynolds and Froude numbers increase, the surface deformation becomes substantial in the downstream of the cylinder. A breaking wave with air entrainment occurs when the ratio of the wave height to the wave length is greater than ∼0.1. Our results provide useful information for design of facilities such as marine constructions and a hydrofoil air pump for drag reduction of ships.
  • Kotaro Takeshima, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 (D) 693 - 700 2011 [Refereed][Not invited]
     
    Since Darrieus turbine is omnidirectional against the wind, it has a great essential advantage in turbulent wind environment. However, a disadvantage on the starting up is known in low velocity conditions of the wind compared with propeller turbines. Darrieus turbine has a low efficiency problem at low tip-speed ratios due to this disadvantage. Some studies have done to overcome this problem, but these have been on the beginning of the way toward the solution. The reason is that the angle of attack for Darrieus blades is changed largely during the rotation relative to the wind direction. In this study, we found a new technique to improve the efficiency. The technique is the providing a large internal cylinder rotating together with the blades, which can control the angle of attack of the blades. We evaluated the influence of cylindrical diameter on the blade performance by the time-averaged velocity distribution and the intensity of the velocity fluctuation comparing between with cylinder and without cylinder. The flow field around the blades is measured with two kinds of instruments. One is Hot Wire Anemometer for analyzing temporal variations of flows, and the other is Particle Image Velocimetry for analyzing the spatial flow structure in detail. Angles of attack and lift coefficients are calculated from the measured relative velocity vector field. As a result, the angles of attack and the lift coefficients are improved in some rotational angles, which are also confirmed by numerical simulations. Copyright © 2011 by ASME.
  • Ryuta Abe, Yuji Tasaka, Ichiro Kumagai, Yuichi Murai, Takatoshi Yanagisawa
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 (D) 2717 - 2722 2011 [Refereed][Not invited]
     
    Internally heated convection is a fundamental phenomenon, largely governing the dynamics of natural systems such as the atmosphere and Earth's mantle. It also plays an important role in industrial applications. Here we have investigated the separation of the top thermal boundary layer in order to understand the cell enlargement and the dynamics of the cell pattern formation. To observe the development of the thermal boundary layer non-invasively, the temperature distribution of the vertical plane in a convective cell was visualized by particle image thermometry (PIT). Micro-encapsulated thermo-chromic liquid crystals (TLCs) were seeded in the test fluid and illuminated by a white light sheet, and scattering light was taken by a digital camera. For quantitative temperature measurement, we have calibrated the temperature changes with the variation of the hue color component. The development of the thermal boundary layer with respect to the Rayleigh number has been investigated. The results show the local Rayleigh number determined from the thickness of the thermal boundary layer, which increases towards a critical local Rayleigh number ∼600. Copyright © 2011 by ASME.
  • Takahisa Shiratori, Yuji Tasaka, Yuichi Murai, Kazuya Oyama, Ichiro Kumagai, Yasushi Takeda
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 (D) 2657 - 2662 2011 [Refereed][Not invited]
     
    Velocity vector fields around a falling sphere in a 1.0 wt % polyacrylamide (PAA) solution are obtained on a vertical cross section by particle image velocimetry (PIV). PAA solution is known as non-Newtonian fluid, which has shear thinning and viscoelastic property. Strain rate tensor fields and deformation fields are calculated from the velocity vector fields in order to visualize the dynamic behavior of the fluid quantitatively. In velocity vector field, two typical flow regions are observed in the wake of the sphere: approaching flow to the sphere, rising flow called "negative wake" [1]. Results show that the strain rate tensor field gives fluid strain at the approaching flow region and the edge of the negative wake. Furthermore deformation history of one portion of the fluid shows that fluid is strained in the approaching flow region, and the strain rate at the edge of the negative wake represents their recovery to the original status of the fluid in the moving frame. Copyright © 2011 by ASME.
  • Yoshihito Miyagishima, Tomoaki Watamura, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 (D) 2669 - 2675 2011 [Refereed][Not invited]
     
    This study aims to clarify the self-organized structure of microbubble plume as a result of two-way interaction between microbubbles and a flow of the surrounding liquid medium. We observed a sequence on a development of microbubble plumes in a thin fluid layer. Here the microbubbles show accumulation pattern with a different wavenumber depending on the height in the vessel. Variation of spatial wavenumber in the developing process was determined from visualization images, and three areas were distinguished in this process (1) the area of rising microbubbles with a large wavenumber in a horizontal direction without time dependence (2) the area of forming a large-scale flow structure, called 'microbubble plume' here, which keeps the primary information, horizontal wavenumber of the bubble accumulation with a large wavenumber (3) the area where the microbubble distribution takes a smaller wavenumber and makes vertical accumulation pattern inside the bubbly flow that is due to the mutual interaction between rising microbubbles and a flow induced by bubbles. To clarify these mutual interactions between liquid and gas phases, we visualized fluid motion of the liquid phase around the microbubble plumes by laser induced fluorescence, LIF. In this way, swaying motions on the tip of rising up bubble plume and liquid phase entrainment into the bubble plumes were visualized. We found the mechanisms for the creation of the self-organized distribution of microbubbles in bubbly flows and its temporal change as the result of the interaction between gas and liquid phase motions in bubbly flows. Copyright © 2011 by ASME.
  • Yoshihito Miyagishima, Tomoaki Watamura, Yuji Tasaka, Ichiro Kumagai, Yuichi Murai
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 77 (784) 2306 - 2315 0387-5016 2011 [Refereed][Not invited]
     
    The evolution of a plume formed by ascending micro-bubbles is investigated by using quantitative visualization to understand the elementary processes that contribute to the inverse energy cascade as small scale flow grows to a large convective flow process. To make the visualization manageable, the plume is confined between two close parallel plates so that the plume-driven convection is restricted to two-dimensions. The results indicate that the bubble plume self-organizes, with a negative diffusion coefficient of buoyancy distribution. A mechanism for the enlargement of the plume is given in terms of two-dimensional flow interaction with the liquid phase. It is confirmed that the kinetic energy is concentrated in the low wavenumber flow from the energy spectra of the liquid phase. © 2011 The Japan Society of Mechanical Engineers.
  • MIYAGISHIMA Yoshihito, WATAMURA Tomoaki, TASAKA Yuji, KUMAGAI Ichiro, MURAI Yuichi
    TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B 一般社団法人 日本機械学会 77 (784) 2306 - 2315 1884-8346 2011 [Not refereed][Not invited]
     
    The evolution of a plume formed by ascending micro-bubbles is investigated by using quantitative visualization to understand the elementary processes that contribute to the inverse energy cascade as small scale flow grows to a large convective flow process. To make the visualization manageable, the plume is confined between two close parallel plates so that the plume-driven convection is restricted to two-dimensions. The results indicate that the bubble plume self-organizes, with a negative diffusion coefficient of buoyancy distribution. A mechanism for the enlargement of the plume is given...
  • Miyuki Yamada, Yuichi Murai
    JOURNAL OF VISUALIZATION 13 (4) 355 - 363 1343-8875 2010/11 [Refereed][Not invited]
     
    A stereoscopic method of identifying story patterns in literary works is newly developed. The pattern is extracted from textual information by the detection of thematically assigned keywords, and depicted as visual imageries. The applicability of the method is demonstrated in several of Shakespeare's plays. The complex scenario patterns in Shakespeare's tragedies are successfully captured with applying the method for two different themes in each play. As the result, the organization of story accompanying multiple themes in a single play has been obtained as a pair of visual imageries, i.e. stereoscopic story visualization. This approach, in combination with a quadrant analysis of the plots, allows us in interpretation further complexity of human psychology in the characters and scene-by-scene transitions in each play.
  • Yuichi Murai, Yuji Tasaka, Yuichi Nambu, Yasushi Takeda, S. Roberto Gonzalez A
    FLOW MEASUREMENT AND INSTRUMENTATION 21 (3) 356 - 366 0955-5986 2010/09 [Refereed][Not invited]
     
    Ultrasound reflects strongly off the gas-liquid interface when there is a large change in acoustic impedance. We exploit this phenomenon to detect the instantaneous position of the interface from the time of flight of pulsed ultrasound. Because the characteristics of the reflected wave depend on the shape and size of the interface relative to the ultrasound wavelength, the single-sensing principle is insufficient to capture the interface for generalized gas-liquid two-phase flows. In the present study, we design and examine three types of ultrasound interface detection techniques: the echo intensity technique, the local Doppler technique, and the velocity-variance technique, and investigate and compare the merits and limitations of each. The results indicate that the echo intensity technique is appropriate for turbulent interfaces that cause ultrasound scattering over wide angles. In contrast, the local Doppler technique is required to capture information from waves reflected from smooth interfaces and bubbles. Finally, we find that the velocity-variance technique works for quasi-steady and periodical two-phase flow, and we apply this technique to horizontal slug flow in a tube. (C) 2010 Elsevier Ltd. All rights reserved.
  • Jumpei Takahashi, Yuji Tasaka, Yuichi Murai, Yasushi Takeda, Takatoshi Yanagisawa
    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 53 (7-8) 1483 - 1490 0017-9310 2010/03 [Refereed][Not invited]
     
    This study determines the flow structure in a convection cell with an internally heated layer by PIV to elucidate the convection cell transition mechanisms. The vertical velocity component is determined and the cell behaviour with respect to Rayleigh number is investigated quantitatively. Cell expansion process is described as a consequence of development of the descending flow at the centre of cells. The results suggest that a spoke-like structure is stable in this system in ideal conditions and a double-cell structure is formed when there are restrictions on the system, i.e. finite lateral boundaries. (C) 2009 Elsevier Ltd. All rights reserved.
  • Shuhei Fujimoto, Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    JOURNAL OF VISUALIZATION 13 (1) 17 - 23 1343-8875 2010/02 [Refereed][Not invited]
     
    Interfacial waves of two immiscible layers in a spin-up container were investigated using experimental visualization. While the interface near the central part rose up, instability waves propagated in an azimuthal direction on the interface. These waves were mainly caused by Kelvin-Helmholtz instability for the velocity difference between two layers during spin-up, but had complicated transient characteristics owing to the rotation in a closed system. We visualized the structure of the interfacial waves by the use of three types of optical characteristics of the interface. Image processing provided the detailed factors of the interfacial waves that were classified in four life stages from their generation to disappearance. The initial generation process involved many frequency modes due to a large velocity difference, and then a low mode stood out during the growth, and disappeared with an ellipsoidal sloshing mode to achieve the rigid rotation in both layers.
  • Tomoaki Watamura, Yuji Tasaka, Yuichi Murai, Yasushi Takeda
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 (772) 2160 - 2167 0387-5016 2010 [Refereed][Not invited]
     
    We investigated the interaction between microbubbles and Taylor-vortices, which are generated in a fluid layer between coaxial-rotating double cylinders. O (10 μm) -diameter hydrogen bubbles were generated by water electrolysis and dispersed into the fluid layer. The maximum void fraction, which is estimated by the input power for the water electrolysis, was smaller than 0.02%. From the time averaged velocity distribution, which is observed by Ultrasonic Velocity Profiling (UVP), these values are changed with different tendency at Re/Re c = 3.0 or 4.0, where Rec is the critical Reynolds number for onset of the primary instability. As initially expected, the existence of the microbubbles does not modify the axial wavelength of the vortices and the frequency of the azimuthal waves either. However, the power of the modulation wave component, which comes from the flow instability, is lowered by the addition of microbubbles at Re/Rec = 8.0 This phenomenon is caused by the rising bubbles with the pattern, which makes inhomogeneous local void fraction.
  • Ichiro Kumagai, Yuichi Murai, Yuji Tasaka, Naoya Nakamura
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 (772) 2152 - 2159 0387-5016 2010 [Refereed][Not invited]
     
    We have conducted laboratory experiments on air-bubble generation by a submerged twodimensional body moving at a constant velocity U0 in order to understand the fundamental flow physics of marine constructions such as pipe lines close to the air-water interface. Measurements of the free surface profile and visualization of the air bubbles yield the threshold and the regime diagrams of the bubble generation, which are described by cross-sectional shape of the cylinders, Reynolds number (Red= U0d/v, where d and v are the vertical thickness of the cylinders and kinematic viscosity of the water, respectively), Froude number (Frh= U0/(gh) 1/2, where h is the depth of the cylinders), and normalized depth of the cylinder (a = h/d). For circular cylinders, as Red and Fr h numbers increase, the surface deformation becomes substantial in the downstream of the cylinder and breaking wave with air entrainment occurs. The bubble generation by the breaking wave is also observed in the case of the elliptic cylinder although the condition of the bubble generation in the Re d-Frh regime diagram is different from that observed in the case of the circular cylinder. In any cases of the cylinders, the ratio of the wave height to the wave length, which should be the physical criterion of the breaking wave with bubble generation, is about 0.1.
  • Hidekazu Kitaura, Yuichi Murai, Yasushi Takeda, Peter J. Thomas
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 (772) 2143 - 2151 0387-5016 2010 [Refereed][Not invited]
     
    Ultrasound Velocity Profiler (UVP) is applied to measurement of two-dimensional velocity vector field of vortex rings in water. The instantaneous flow field passing through the measurement section is reconstructed from spatio-temporal distribution of velocity component obtained along two different ultrasound measurement lines. The method of reconstruction is valid when vortex rings have axisymmetric structure having constant translational velocity at the measurement section. Using this principle, vortex ring subject to background rotation is also presented to discuss the effect of weak Coriolis force on formation process of vortex rings.
  • Yuichi Murai, Yuji Tasaka, Daiki Tanaka, Yasushi Takeda, Hirotaka Takeuchi
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 (765) 747 - 754 0387-5016 2010 [Refereed][Not invited]
     
    Wake structure of permeable object is one of great concerns for wind engineering, chemical processing, and fluid machineries. It produces the drag greater than the same-sized solid object due to friction dominant nature even at Reynolds numbers higher than 10s. In order to characterize the wake structure in such a condition, we measure the flow field around the permeable cylinder made of wire mesh and annularly arrayed thin cylinders. The parametric study presents a spatially delayed amplification of turbulence due to vortex shedding in two frequencies compound in the wake. We also measure the flow for a rotating permeable cylinder to find the interaction between circulating elements and macroscopic behavior of flow. The result indicates a curtain effect of the elements to expand the momentum loss region behind the rotating cylinder.
  • Yuichi Murai, Ichiro Kumagai, Yuji Tasaka, Yasushi Takeda, Yoshiaki Takahashi
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 (763) 483 - 485 0387-5016 2010 [Refereed][Not invited]
     
    Installation of hydrofoils to ship wetted surface enables bubble generation to be realized with power consumption much lower than conventional bubble generators. With help of this principle, net effect of frictional drag reduction for ships can be improved. We have already obtained around 10% net power-saving efficiency for a cargo ferry throughout about half a year. The power-saving has a large potential to be improved more by considering multiphase fluid dynamics in terms of the hydrofoil-water-air triple interaction. This paper presents the principle of the bubble generation, the estimation of net power-saving, and the flow structure visualized by experimental and numerical approaches.
  • Akinari Shigetomi, Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 76 (763) 366 - 368 0387-5016 2010 [Refereed][Not invited]
     
    Wind tunnel experiments are conducted to explore the flow field around two widely spaced Savonius windmills that interact to each other. The flow visualization with single and two arranged windmills is conducted with Particle Image Velocimetry (PIV). The mean and the fluctuation velocities are evaluated from PIV so that the interaction mechanism between two windmills is classified into the mean and the turbulent components. The best arrangement of two windmills is found to be a coupling of them with counter rotation at an inclined angle to the main flow. The pressure distribution on the best coupling condition is obtained by the data analysis of PIV, which indicates how the pressure field interferes positively to promote the rotations. From the present finding both for one-way and two-way interactions, the phase optimization for blades of each windmill is suggested for further promotion of the power-increasing interaction.
  • Tomoaki Takeuchi, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 21 (1) 1 - 10 0957-0233 2010/01 [Refereed][Not invited]
     
    We investigate the tracer gas pulse injection method for flowmetering of natural gas pipelines. The principle of the measurement consists of detecting the passage of the pulse at two locations along the pipeline, from which the time of passage is calculated. The measurement accuracy depends on how the pulse form evolves due to turbulent diffusion and convective distortion in the pipe, as well as due to the influence of bends. We discuss these factors to evaluate the applicability of the method to pipelines of kilometer distances. We also perform a three-dimensional numerical analysis to understand the spatial pulse dispersion, and numerical analysis shows that the influence of pipe bends was not significant. Both experimental and theoretical results indicate the existence of axial diffusion coefficients, even in pipelines with bends. These results enable us to predict the evolution of the pulse concentration profile. Finally, we demonstrate acceptable precision for practical flowmetering applications in actual utility pipelines.
  • Jamshidnia Hamidreza, Tasaka Yuji, Murai Yuichi, Takeda Yasuhsi
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2010 181 - 182 2010 
    The vertical flow structure around a standing baffle in a rectangular open channel has been investigated by an Ultrasonic Velocity Profiler (UVP). Spatial distributions of the time-averaged of vertical velocity components and relative turbulent intensities for vertical components at vertical measuring lines indicate how the flow structure changes from up- to downstream of it. At baffle's upstream they indicate the flow structure of the uprising flow. But behind the baffle indications of vortex shedding and flow separation such as the prominent peak values in the relative turbulent intensity profiles are observed. Spatio-temporal distributions of the vertical velocity at up- and downstream sections confirm the existence of periodic change of flow direction near the baffle edge at its downstream which can be attributed to the vortex shedding. Smoothed space-dependent power spectra indicate the existence of some peak structures near the baffle's edge at its downstream which are corresponding to the periodic nature of flow concentrated mainly near the baffle's edge in the spatio-temporal vertical velocity distributions. Such peak structures could not be observed for the upstream sections.
  • MURAI Yuichi
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2010 121 - 122 2010 
    Ultrasound velocity profiling obtains 1-D 1-C flow velocity distribution from a single ultrasound transducer, and is suitable for monitoring one-component dominant flow field such as in pipes. Instead, two-dimensional flow structure such as vortex cannot be directly observed. This note reports several trials done by the author in terms of two-dimensional flow field reconstruction that is classified into three flow confifurations; transverse, rotational, and outward measurements.
  • W. H. Liu, T. Wan, W. Cheng, Yuichi Murai
    6TH INTERNATIONAL SYMPOSIUM ON MULTIPHASE FLOW, HEAT MASS TRANSFER AND ENERGY CONVERSION 1207 646 - + 0094-243X 2010 [Refereed][Not invited]
     
    The flow pattern of gas-liquid two-phase flow in an aeration tank is of critical effect upon mass transfer by the convection. Bubble plume provides unsteadily fluctuating two-phase flow during the aeration. This paper the study on the unsteady structure of bubble plume is dealt with from experiment. The time-serial bubble plume images of different cases in tank have been analyzed. The RCC-PIV has been employed to calculate the velocities in those cases, and then the time-serial vortex, the total turbulence intensity, the time-serial streamline are obtained. It has been shown that the aspect ratio and void fraction are the dominant factors influencing the unsteady structure of bubble plume. When the aspect ratio is unity and the void fraction gets higher, the bubble plume has symmetrical vortex structure and longest residence time, which is beneficial for optimizing the aeration system and enhancing the applied range of bubble plume.
  • Yuichi MURAI, Yuji TASAKA, Yuichi NAMBU, Yasushi TAKEDA, S. Roberto, GONZALEZ A
    Flow Meas. Inst. 21 (3) 356 - 366 0955-5986 2010 [Refereed][Not invited]
  • Koji Okamoto, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 20 (11) 0957-0233 2009/11 [Not refereed][Not invited]
  • Yuichi Murai, Shoko Ohta, Akinari Shigetomi, Yuji Tasaka, Yasushi Takeda
    MEASUREMENT SCIENCE AND TECHNOLOGY 20 (11) 114003  0957-0233 2009/11 [Refereed][Not invited]
     
    A method for measuring the spatial distribution of the void fraction in bubbly two-phase flow is presented. The method is referred to as ultrasonic void fraction profiling since it is based on the signal processing of an ultrasonic pulse scattering on a bubble interface. The method is established using two processes for the ultrasonic sensing of bubbles. One approach is to detect the bubble interface along a measurement line, i.e. the path of the ultrasonic pulse in the liquid. The interface is captured using two types of signal-processing schemes: the echo intensity method and the Doppler method. The other approach is to reconstruct the void fraction profile from the number of bubble interfaces. A theoretical formula for the estimation is proposed by considering ultrasonic reflection in a suspension of bubbles. The validity of the formula is examined with theoretical and numerical bases. Finally, the method developed here is applied to four flow configurations for the demonstration, in which the void fraction profile governs the modulation of liquid flow field.
  • H.J. Park, Y. Oishi, Y. Tasaka, Y. Murai, Y. Takeda
    Journal of Physics: Conference Series 147 (12037) 012037 - 13 2009/03 [Refereed][Not invited]
  • Huang Jian, Murai Yuichi, Yamamoto Fujio
    JOURNAL OF HYDRODYNAMICS 21 (1) 93 - 99 1001-6058 2009/02 [Refereed][Not invited]
     
    Our previous Study showed that the frictional drag decreases with increasing void fraction at Re > 1300, while it increases at Re < 1000. Decomposition of the Reynolds shear stress also implied that bubbles induce isotropy of turbulence. In order to confirm our previous analysis and to further investigate flow fields in the vicinity of bubbles, we analyze velocity fluctuations on the quadrant space in the streamwise and transverse directions (u'-v' plane). Here, we focus oil two specific Reynolds numbers (at Re approximate to 900 and approximate to 14 10, which are close to the laminar-to-turbulent transition regime) and discuss bubble effects on sweep (u'>0, v'<0) and ejection (u'<0, v'>0) events as a function of the Reynolds number. We also illustrate velocity fluctuations in the vicinity of all individual bubble and a swarm of bubbles oil the u'-v' coordinates. The results show that a bubble swarm suppresses the velocity fluctuations at Re approximate to 1410.
  • J. Huang, T. Suzuki, Y. Murai, F. Yamamoto
    Journal of Physics: Conference Series 147 1742-6596 2009 
    Our previous study showed that the frictional drag decreases with increasing void fraction at Re > 1300, while it increases at Re < 1000. Decomposition of the Reynolds shear stress also implied that bubbles induce isotropy of turbulence. In order to confirm our previous analysis and to further investigate flow fields in the vicinity of bubbles, we analyze velocity fluctuations on the quadrant space in the streamwise and transverse direction (u' - v' plane). Here, we focus on two specific Reynolds numbers (at Re 900 and 1410, which are close to the laminar-to-turbulent transition region) and discuss bubble effects on the sweep (u' > 0, v' < 0) and ejection (u' < 0, v' > 0) events as a function of the Reynolds number. We also illustrate the velocity fluctuations in the vicinity of an individual bubble and a swarm of bubbles on the u' - v' coordinates. The result shows that a bubble swarm suppresses the velocity fluctuations at Re 1410. We then rearrange the scatted PTV vectors and compute power spectra of the kinematic energy of each velocity component. It only indicates that the elongated bubble suppresses low frequency Ew at Re 1410. © 2009 IOP Publishing Ltd.
  • Visualization of transient interfacial waves induced by spin-up of two immiscible fluid layers
    Journal of Visualization 10 1007  2009 [Refereed][Not invited]
  • S. Roberto Gonzalez A, Yuichi Murai, Yasushi Takeda
    Advances in Chemical Engineering 37 1 - 27 0065-2377 2009 [Refereed][Not invited]
     
    Ultrasonic velocity profiler (UVP) measurements are performed for gas-liquid two-phase flow. The UVP measurements are conducted in a rectangular channel and in a pipe, both horizontally oriented. The liquid velocity measurements and ultrasound echo intensity are used to locate the position of the gas-liquid interface information. Liquid velocity data are analyzed to obtain the bubble interface for the study of the mechanism of drag reduction. The peak ultrasound echo intensity is used to locate the position of the gas-liquid interface in a pipe for the estimation of the liquid flow rate. No gas-flow rate calculations are performed. The experiments in the pipe are performed using three UVP-DUO systems simultaneously to obtain a more accurate shape for the gas-liquid interface. The tests conducted belong to three different flow regimes: stratified, elongated bubble, and slug flow. The results show very good agreement with the actual liquid flow rates. © 2009 Elsevier Inc. All rights reserved.
  • Tetsushi Kanda, Yuichi Murai, Yuji Tasaka, Yasushi Takeda, Hideaki Tezuka, Michitsugu Mori
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 75 (751) 561 - 563 0387-5016 2009 [Refereed][Not invited]
     
    The present study aims at developing a 3-D trajectory measurement system for birds, in particular for endangered species, e.g. raptorial, flying around wind turbines as a part of its complete system to be applied for prevention from bird strike. The method is based on stereoscopic photography, which is similar to 3-D particle tracking velocimetry. For stabilizing the bird-image detection performance in natural background, the time differential technique is proposed and examined considering constraint of time of day and weather on the measurement. All tests are conducted in outdoor farm. For the demonstration purpose, 3-D trajectories of crows flying above the farm are obtained and shown in order to assess the effectiveness of stereoscopic photography for live birds.
  • Shoko Ohta, Akinari Shigetomi, Yuji Tasaka, Yuichi Murai, Yasushi Takeda, Munehiko Hinatsu
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 75 (751) 538 - 540 0387-5016 2009 [Refereed][Not invited]
     
    Friction drag accounts for 80% of the total drag for large ships, and drag reduction realized by injecting air bubbles is expected as one of the feasible ways because of less environmental impact. We have measured the turbulent boundary layer structure altered by bubbles beneath 127 m-ship by means of ultrasonic Doppler velocimetry. This short paper mainly describes the measurement method of seawater velocity profiles and the some typical results on the influences of bubbles.
  • M. Yamada, Y. Murai
    JOURNAL OF VISUALIZATION 12 (2) 181 - 188 1343-8875 2009 [Refereed][Not invited]
     
    With the rapid advance in information technology, the applicability of computers has moved from the scientific field towards simulating human intelligence. We are already familiar with using computers to produce music and art and for language translation. A further use is in understanding traditional man-made products; best exemplified by literary works. In this study, we focus on enabling a computer to visualize the meaning of stories. Four world-famous plays by William Shakespeare have been chosen to demonstrate how the visualization scheme works in grasping the meaning of the stories. The scheme employs primitive keyword detection and ellipsoidal differential equations to create a visual imagery of the story. This methodology ensures uniqueness in the visualization of an individual work. In addition, color palettes obtained from pictures relevant to each story are used to enrich the consistency between the visual sense and the meaning of the story.
  • FUJIMOTO Shuhei, MURAI Yuichi, TASAKA Yuji, KUMAGAI Ichiro, TAKEDA Yasushi
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2009 89 - 90 2009 
    We report a little-known deformation phenomenon occurring at the interface between two immiscible liquids. The two liquids are in a cylindrical container and set into motion by a rotating lid positioned above the interface. The upper liquid is about 100 times viscous than the lower and a difference in density between the liquids is about 3.5 %. Depending on the rotational speed of the lid (Ω), the topology of the interface changes drastically: from low Ω to high Ω, a simple hump, a cusp shape, a shape like Mt. Fuji, and a shape like a bell appears in sequence.
  • MURAI Yuichi, Yoshida Koji, TASAKA Yuji, TAKEDA Yasushi
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2009 63 - 64 2009 
    Vortex patterns in Taylor-Couette flow are uniquely determined with Reynolds number in single-phase medium. It never contains hysteresis in any transition from one to another for sufficiently large aspect ratio. In contrast, inclusion of bubbles provides a remarkable hysteresis in wavy vortex regime, snowing a periodic switching between spiral and toroidal modes. From this fact, space-time four-dimensional mechanism on bubble-vortex interaction is to be deduced from a number of physical aspects. Moreover, the interaction is tightly relevant to frictional drag reduction that occurs at high gain factor up to 10. We report on the interpretation on this phenomenon in this paper.
  • Y. Murai, M. Yamada
    JOURNAL OF VISUALIZATION 12 (1) 5 - 5 1343-8875 2009 [Refereed][Not invited]
  • Takamasa SUZUKI, Yoshihiko OISHI, Yuichi MURAI, Yuji TASAKA, Yasushi TAKEDA
    J. Phys: Conference Series 147 012012  2009 [Refereed][Not invited]
  • Koji YOSHIDA, Yuji TASAKA, Yuichi MURAI, Yasushi TAKEDA
    J. Phys: Conference Series 147 012013  2009 [Refereed][Not invited]
  • Frictional Drag Reduction Promoted by Intermittent Bubble Injection
    H.-J. PARK, Y.OISHI, Y.TASAKA, Y.MURAI, Y.TAKEDA
    European Drag Reduction and Flow Control Meeting 2008 Book of Abstracts 34 - 35 2008/09 [Refereed][Not invited]
  • Yuichi Murai, Hiroshi Oiwa
    FLUID DYNAMICS RESEARCH 40 (7-8) 565 - 575 0169-5983 2008/07 [Refereed][Not invited]
     
    The effective viscosity of bubbly liquids is measured using the Stokes drag of a falling sphere, i.e. falling sphere viscometry. This method can evaluate the influence of a bubble's transient deformation. Viscosity relative to a single-phase fluid is directly obtained by the terminal falling velocities of the sphere. When bubbles are distributed around the sphere up to a void fraction of alpha, the following results are obtained. The relative viscosity for spherical bubble dispersion agrees with the Stokes-Einstein formula; 1 + alpha. For large capillary numbers, relative viscosity converges to approximately 1 - (5/3)alpha because bubble deformation is fully yielded. Between these two states, relative viscosity has a value higher than in simple shear flow. The critical capillary number is found to be 3.5, being five times as that of simple shear flow. The viscosity-increasing mechanism for trans-critical capillary numbers is deduced from the fact that bubbles have transient deformation along the streamline. (c) 2008 The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.
  • Jian Huang, Yuichi Murai, Fujio Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 19 (2) 93 - 105 0955-5986 2008/04 [Refereed][Not invited]
     
    To investigate the effect of microbubble injection into a turbulent boundary layer, we measure the velocity fields of gas-liquid two-phase flow in a horizontal water channel with a Particle Tracking Velocimetry (PTV) technique. In this study, we focus on a thin shear layer where the Reynolds shear stress is the highest. The effect of the shallow focal depth-of-field (DOF) in a lens system assists to improve the spatial resolution of the PTV results. Considering the distribution of luminous flux, we first enhance the illumination intensity to label the objects on images. With their assistance together with an image processing filter, we can then improve the in-depth resolution of tracer particles and determine their positions more accurately. We apply this shallow DOF-based PTV technique to measure the streamwise and spanwise velocity components and visualize the motion of bubbles relative to continuous phase in the near-wall region at three downstream positions. The result shows that the averaged velocity right downstream of the bubble injector clearly decreases due to microbubbles. The local instantaneous flow structure around bubbles shows no clear coherence because of highly turbulent background; however, the frequency spectrum analysis finds that the bubbles reduce the kinetic energy in a frequency range higher than the bubble passing frequency. (C) 2008 Published by Elsevier Ltd.
  • Yuichi Murai, Hiroshi Oiwa, Yasushi Takeda
    PHYSICS OF FLUIDS 20 (3) 1 - 8 1070-6631 2008/03 [Refereed][Not invited]
     
    Frictional drag reduction due to the presence of small bubbles is investigated experimentally using a Couette-Taylor flow system; i.e., shear flow between concentric cylinders. Torque and bubble behavior are measured as a function of Reynolds number up to Re = 5000 while air bubbles are injected constantly and rise through an array of vortical cells. Silicone oil is used to avoid the uncertain interfacial property of bubbles and to produce nearly monosized bubble distributions. The effect of drag reduction on sensitivity and power gain are assessed. The sensitivity exceeds unity at Re < 2000, proving that the effect of the reduction in drag is greater than that of the reduction in mixture density. This is due to the accumulation of bubbles toward the rotating inner cylinder, which is little affected by turbulence. The power gain, which is defined by the power saving from the drag reduction per the pumping power of bubble injection, has a maximum value of O (10) at higher Re numbers around 2500. An image processing measurement shows this is because of the disappearance of azimuthal waves when the organized bubble distribution transforms from toroidal to spiral modes. Moreover, the axial spacing of bubble clouds expands during the transition, which results in an effective reduction in the momentum exchange. (C) 2008 American Institute of Physics.
  • Y. Murai, Y. Oishi, Y. Tasaka, Y. Takeda
    JOURNAL OF VISUALIZATION 11 (1) 63 - 70 1343-8875 2008/01 [Refereed][Not invited]
     
    Particle tracking velocimetry (PTV) is applied for measuring the motions of luminous particles in fireworks. The objective of the study is to clarify the technical problems encountering in large-scale quantitative visualization in natural environment. The major problems are found to be uncontrolled background in nature, low pixel resolution relative to particle size, and large perspective. The ways to deal with these problems in current technological level are discussed. In the application, two cameras are located at 1.3 km from the launching point with 30-degree opening angle to implement 3-D PTV. The transient 3-D velocity distributions of around 200 m-scale diameter fireworks are obtained during the light emission from the explosion till burnout. Moreover, the evolution of the mean particle diameter that decreases continuously with the combustion is estimated with the measured velocity information by the particle's equation of motion.
  • FURUYA Naoki, FUJIMOTO Shuhei, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2008 93 - 94 2008 
    In this study, we aim to develop a scheme for estimating properties of viscoelastic liquid, by means of Ultrasonic Velocity Profiler (UVP). Unsteady velocity profiles of a visco-elastic fluid driven by sudden spin are measured with it to find out the behavior of the fluid motion as well as to assess the visco-elastic properties. The measurement result shows typical response due to the elastic property. In addition, we carried out numerical simulation of the transient flow based on Bingham model considering yield stress, to clarify the oscillatory behavior.
  • Yuuta NOMURA, Yuji TASAKA, Yuichi MURAI, Yasushi TAKEDA
    J. Phys: Conference Series 137 012001 - 6 2008 [Refereed][Not invited]
  • Ultrasonic Doppler visualization of slug flow in a horizontal pipe
    S.R. Gonzales, Y.MURAI, Y.TASAK, Y.OISHI, Y.TAKEDA
    Proc. 13th International Symposium on Flow Visualization 2008 [Refereed][Not invited]
  • Interaction Between Streamwise Vortex and Bubbles in Horizontal Channel Flow
    T.SUZUKI, Y.OISHI, Y.MURAI, Y.TASAKA, Y.TAKEDA
    Proc. 13th International Symposium on Flow Visualization 2008 [Refereed][Not invited]
  • Y.OISHI, Y.MURAI, Y.TASAKA, Y.TAKEDA
    Proc. 6th Intl. Sym. Measurement Tech. for Multiphase Flows 147 USB-proceedings, No. 5, Book o - 14 2008 [Refereed][Not invited]
  • Yuichi Murai, Kazumasa Inaba, Yasushi Takeda, Fujio Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 18 (5-6) 223 - 229 0955-5986 2007/10 [Refereed][Not invited]
     
    Backlight imaging tomography is used to experimentally investigate interfacial structures of gas-liquid two-phase flow in circular tubes. The tomography method is based on the attenuation of visible light that causes the inside of the liquid phases to be colored with dye. Increasing the number of light projections provides accurate phase distributions to be reconstructed by a linear backward projection scheme. After the reconstruction performance is examined with numerical simulations for several test cases, the method is applied to slug flows that have complicated 31) interfaces from turbulence. Interfacial structures are compared between straight and helical tubes to determine the effect of centrifugal acceleration. The result demonstrates that centrifugal acceleration provides a liquid-clinging layer on the inner wall against gravity while a high-speed collision of liquid with the top wall happens in a straight tube. (c) 2007 Elsevier Ltd. All rights reserved.
  • Yuichi Murai, Taishi Nakada, Takao Suzuki, Fujio Yamamoto
    MEASUREMENT SCIENCE AND TECHNOLOGY 18 (8) 2491 - 2503 0957-0233 2007/08 [Refereed][Not invited]
     
    Particle tracking velocimetry (PTV) is applied to flows around a Savonius turbine. The velocity vector field measured with PTV is utilized to estimate the pressure field around the turbine, as well as to evaluate the torque performance. The main objective of the work is the establishment of the pressure estimation scheme required to discuss the turbine performance. First, the PTV data are interpolated on a regular grid with a fourth-order ellipsoidal differential equation to generate velocity vectors satisfying the third-order spatio-temporal continuity both in time and space. Second, the phase-averaged velocity vector information with respect to the turbine angle is substituted into three different types of pressure-estimating equations, i.e. the Poisson equation, the Navier-Stokes equation and the sub-grid scale model of turbulence. The results obtained based on the Navier-Stokes equation are compared with those based on the Poisson equation, and have shown several merits in employing the Navier-Stokes-based method for the PTV measurement. The method is applied to a rotating turbine with the tip-speed ratio of 0.5 to find the relationship between torque behaviour and flow structure in a phase-averaged sense. We have found that a flow attached to the convex surface of the blades induces low-pressure regions to drive the turbine, namely, the lift force helps the turbine blades to rotate even when the drag force is insufficient. Secondary mechanisms of torque generation are also discussed.
  • Motion of Microbubbles Relative to Streamwise Vortices in the Wall Turbulence
    Y.OISHI, Y.MURAI, Y.TASAKA, Y.TAKEDA
    Abstracts of the6th International Conference on Multiphase Flow S1_Wed_C_37, CD-ROM 55  2007/08 [Refereed][Not invited]
  • Yuichi Murai, Hiroshi Fukuda, Yohiko Shi shi, Yoshiaki Kodama, Fujio Yamamoto
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 33 (2) 147 - 163 0301-9322 2007/02 [Refereed][Not invited]
     
    Microbubble and air film methods are believed to be applicable to skin friction reduction in ships. Small bubbles are dispersed into the turbulent boundary layer in the former case, and wide air layers cover the wall surface in the latter case. Previous studies did not specifically address the intermediate case between the microbubble and air film conditions. This study is concerned with the possibility and mechanism of drag reduction using relatively large air bubbles compared to the boundary layer thickness in a horizontal turbulent channel flow. The relationship between local skin friction and the bubble's interfacial structure is investigated by synchronizing the measurement of wall-shear stress with the image acquisition of bubbles. The bubble sizes range from 2 to 90 mm approximately. As a result, a negative correlation between the local skin friction and the local void fraction is confirmed by the time-resolved measurement. A new observation is the fact that the local skin friction decreases drastically in the rear part of individual large bubbles, and rapidly increases after the bubble's rear interface passes. This characteristic underlies the bubble-size dependency of the average skin friction in the intermediate bubble size condition. (c) 2006 Elsevier Ltd. All rights reserved.
  • Wen Cheng, Chun-Di Yang, Yuichi Murai, Fujio Yamamoto
    AIP Conference Proceedings 914 453 - 457 0094-243X 2007 
    Aeration plays an important role in the treatment of activated sludge. The aeration performance is deeply affected by the movement law of bubble liquid flow in aeration tank. In order to discuss the influence of gas-phase, liquid-phase motions in an aeration tank on the sewage disposal, three kinds of boundaries and initial conditions were applied in the experiment to study the law of two-phase flow. A developed two-equation turbulence model was employed in this paper. Results obtained by experiment are compared with those from the mathematical model. It is found that the results of measurement and simulation agree with each other. © 2007 American Institute of Physics.
  • Yoshihiko Oishi, Hiroshi Fukuda, Yuichi Murai
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 73 (6) 1298 - 1306 0387-5016 2007 
    Flow field modified by a single large bubble in a horizontal wall turbulent boundary layer is measured by particle tracking velocimetry. We focus on intermediate bubble size being comparable to the thickness of boundary layer to find out the events altering the original turbulent shear stress field. The results are all presented by quantities relative to single-phase flow on Lagrangian coordinate that moves with the bubble. The measurement results reveal bubble-produced secondary flow around itself, which involves twin roll vortices, separation on the bubble surface, and strong sweeping flow. For a small and nearly spherical bubble, the sweeping flow is provided strongly to enhance the turbulent momentum exchange while negative exchange is detected for a large flat bubble. This effective length approximately corresponds to the vertical size of the bubble.
  • MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi, ISHIKAWA Masaaki
    Transactions of Visualization Society of Japan The Visualization Society of Japan 27 (107) 253 - 258_1 0916-4731 2007
  • KANDA Tetsushi, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 27 (2) 91 - 92 0916-4731 2007 
    This study is positioned as a basic research for PIV measurement of large spatial airflow using soap bubbles. Bubbles are applied as for airflow tracer because of less environmental impact for the application in nature. The bubble dynamics characteristics are investigated by comparing with smoke-based PIV measurement. The inverse analysis method is constructed to obtain airflow vector field from the bubble vector field, which takes into account the fundamental force components of the bubbles.
  • YANO Kanako, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, YANAGISAWA Takatoshi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 27 (1) 271 - 272 0916-4731 2007 
    We attempted to measure the velocity distribution of thermal plume by means of ultrasonic velocity profiling, UVP. To investigate a behavior of the plume at velocity field, both of the visualization and UVP measurement was done in transparent liquids, water and glycerol solution. Ascending velocity of the plume obtained by each method showed good agreement each other. Spatio-temporal velocity distribution measured by UVP further showed the periodic separation of the thermal boundary layer, which is difficult to be observed by the visualization. The velocity distribution of the plume appearing in liquid gallium was also measured by UVP and applicability of the measurement system on the thermal plume measurement was confirmed.
  • KANDA Tetsushi, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 27 (1) 161 - 162 0916-4731 2007 
    This study aims to develop a PTV measurement method which is applicable to large spatial airflows, such as flows around windmill. Bubbles (soap bubbles) are considered as airflow tracer because of less environmental impact for the application in nature. The motion characteristics of the bubbles in high acceleration field are evaluated by comparing with ordinary smoke-based PIV. The size-dependent traceability of the bubbles for flows around an airfoil that involves separation in high attack angle is reported in this paper.
  • MURAI Yuichi, OIWA Hiroshi, TAKEDA Yasushi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 27 (1) 129 - 130 0916-4731 2007 
    Microbubble drag reduction in Taylor-Couette flow system is investigated experimentally. We measured torque acting on rotating inner cylinder and evaluated the power gain of the drag reduction as function of Reynolds number from 600 to 4, 500. The results have shown that the gain increased up to 20 in the case that the bubble distribution organized by Taylor cell was altered from toroidal to spiral structures. This range coincided with the fact that the wavelength of the bubble-cluster spacing was elongated due to bubble-to-vortex interaction.
  • SUZUKI Takamasa, OISHI Yoshihiko, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 27 (1) 113 - 114 0916-4731 2007 
    Longitudinal vortices sensitively govern the turbulent momentum transport in boundary layers. In order to obtain the fundamental knowledge on microbubble drag reduction mechanism, the interaction between the vortices and the bubbles are experimentally investigated in this study. The longitudinal vortex is generated artificially from a delta wing installed inside the shear layer in a channel. According to PTV measurement, the vorticity is reduced by presence of bubbles compared to the original. Significant displacement of the vortex core is also confirmed to explain the momentum transfer modification. Moreover, numerically simulated bubble trajectories on the measured velocity yields to high persistency of the interaction for small bubbles.
  • Tetsushi Kanda, Yuji Tasaka, Yuichi Murai, Yasushi Takeda
    FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT AMSE/JSME FLUIDS ENGINEERING SUMMER CONFERENCE VOL 1, PTS A AND B 679 - 686 2007 [Refereed][Not invited]
     
    Availability of particle tracking velocimetry (PTV) that is applied to movie images of soap bubbles in airflow is investigated experimentally. This study is positioned as a basic research for measuring environmental flow with a large spatial scale, such as flows around building, trees, and near-ground airflow boundary layer. Instead of solid fine particles, soap bubbles are used as the airflow tracer for reducing environmental impact. Typical bubble size provided by the present bubble generator is controlled around 20mm, at which the bubbles obviously have relative velocity to the airflow. We report three topics on the bubble tracking velocimetry(BTV) in this paper: 1) optics of bubble-imaging for quantitative visualization, and application to 3-D) visualization using color illumination, 2) theoretical estimation of bubble's relative velocity to airflow based on an equation of bubble's translational motion, 3) comparison of velocity vector field obtained by the BTV with that from cross-correlation PIV applied for smoke image. For the latter two topics, airflow around a NACA airfoil is chosen as the target of BTV measurement since it causes significant slip motion of soap bubbles from the airflow that accompanies shear rate, convective acceleration, pressure gradient, and separation.
  • Cheng Wen, Zhang-Bin Wang, Yuichi Murai, Fujio Yamamoto
    MULTIPHASE FLOW: THE ULTIMATE MEASUREMENT CHALLENGE, PROCEEDINGS 914 877 - + 0094-243X 2007 [Refereed][Not invited]
     
    In bubbly two-phase flow, the gas phase and liquid phase have different flow fields. The mathematical expression for the motion of a small bubble at low Re number has been already established, the liquid velocity along the trajectory of the bubble is calculated inversely by using the motion equation. Whole field liquid flow structure has also estimated using a spatial and/or temporal interpolation method. This paper proposes an algorithm for estimating the liquid phase flow field based on measurement data on bubble data on bubble motion. The applicability of the algorithm is examined with Taylor-Green vortex flow as an analytical test case. Meanwhile, The result based on the theory, has been applied to reconstruct liquid phase velocity field by using the data of bubble velocity in an aeration tank.
  • 水平壁面乱流境界層内の単一気泡がもたらす流動場変調
    大石義彦, 福田浩士, 村井祐一
    日本機械学会論文集 B編 73 (730) 1298 - 1306 2007 [Refereed][Not invited]
  • Alternation of a Pair of Streamwise Vortex by Bubbles
    T.SUZUKI, Y.OISHI, Y.MURAI, Y.TASAKA, Y.TAKEDA
    Bulletin of 60th Annual Meeting of the Division of Fluid Dynamics, American Physical Society 52 (17) 136  2007 [Refereed][Not invited]
  • Particle Image Velocimetry for Air Flows Behind Permeable Cylinders
    H.TAKEUCHI, Y.OISHI, Y.TASAKA, Y.MURAI, Y.TAKEDA
    The 2nd Hokkaido University - Seoul National University Symposium on Mechanical and Aerospace Engineering 88  2007/01 [Not refereed][Not invited]
  • PTV Assessment of Friction-Modifying Events in Bubbly Turbulent Shear Flow
    Y.OISHI, H.FUKUDA, Y.MURAI, F.YSMSMOTO, Y.TAKEDA
    Proc. The5th Int. Symposium on Measurement Techniques for Multiphase Flows 567 - 571 2006/12 [Refereed][Not invited]
  • Stereoscopic Particle Tracking Velocimetry Applied to Fireworks
    M.MORINAGA, Y.OISHI, Y.TASAKA, Y.MURAI, Y.TAKEDA
    APS Gallery of Fluid Motion Poster Session 2006/11 [Refereed][Not invited]
  • Takehiro Ido, Yuichi Murai
    FLOW MEASUREMENT AND INSTRUMENTATION 17 (5) 267 - 275 0955-5986 2006/10 [Refereed][Not invited]
     
    A new type of interpolation algorithm for particle tracking velocimetry is proposed. The algorithm is established based on a combination of ellipsoidal differential equations, i.e. a recursive process from a lower to a higher order interpolation. Each equation is solved as a boundary value problem by using the discrete velocity vector information as boundary conditions. In this paper the performance of the interpolation scheme, such as errors and cross correlations, is examined using the Taylor-Green vortex flow and isotropic turbulent flow. The examination results reveal that the recursive process from linear to hexagonal interpolation provides the best reconstruction in comparison to the single process. A quantitative evaluation is also carried out for integral and derivative information of the velocity vector, such as stream function and vorticity. (c) 2006 Elsevier Ltd. All rights reserved.
  • Y. Murai, Y. Oishi, Y. Takeda, F. Yamamoto
    EXPERIMENTS IN FLUIDS 41 (2) 343 - 352 0723-4864 2006/08 [Refereed][Not invited]
     
    Particle tracking velocimetry (PTV) is applied to a bubbly two-phase turbulent flow in a horizontal channel at Re = 2 x 10(4) to investigate the turbulent shear stress profile which had been altered by the presence of bubbles. Streamwise and vertical velocity components of liquid phase are obtained using a shallow focus imaging method under backlight photography. The size of bubbles injected through a porous plate in the channel ranged from 0.3 to 1.5 mm diameter, and the bubbles show a significant backward slip velocity relative to liquid flow. After bubbles and tracer particles are identified by binarizing the image, velocity of each phase and void fraction are profiled in a downstream region. The turbulent shear stress, which consists of three components in the bubbly two-phase flow, is computed by analysis of PTV data. The result shows that the fluctuation correlation between local void fraction and vertical liquid velocity provides a negative shear stress component which promotes frictional drag reduction in the bubbly two-phase layer. The paper also deals with the source of the negative shear stress considering bubble's relative motion to liquid.
  • ITOH Tetsuya, MURAI Yuichi, UENO Yasutaka, OIWA Hiroshi, MIYAGI Naoki, YAMAMOTO Fujio
    Transactions of the Visualization Society of Japan The Visualization Society of Japan 26 (4) 27 - 32 1346-5260 2006/06 [Refereed][Not invited]
     
    Flow visualization of an inscribed gear pump is carried out to grasp the flow structure governed by the deformation and the volume change of the fluid chamber surrounded by the inner and outer trochoid gears. A platelet type of light-reflecting tracer particles "Kalliroscope" is adopted and applied to the visualization of flow patterns using a transparent model of the pump. Upon taking phase-statistic for the time serial images, the dependence of the flow on Reynolds number and the volumetric efficiency is evaluated.
  • Waveforms of Local Frictional Drag Modified by Bubbles
    Y.OISHI, Y.MURAI, Y.TASAKA, Y.TAKEDA, Y.KODAMA
    Proc. European Drag Reduction and Flow Control Meeting 25 - 26 2006/04 [Refereed][Not invited]
  • Yuichi MURAI, Hideki FUJII, Yuji TASAKA, Yasushi TAKEDA
    Journal of Fluid Science and Technology The Japan Society of Mechanical Engineers 1 (1) 12 - 23 1880-5558 2006 [Refereed][Not invited]
     
    Ultrasound velocity profiler (UVP) is applied to measurements of a horizontal turbulent bubbly channel flow to ascertain the mechanism of bubble-induced frictional drag reduction. Typical parameter regimes of the target flow are Re number of 0.6-6.0 x104, void fraction of 0-3%, and bubble diameter of 10-50mm. Since the UVP system only outputs velocity profiles on an ultrasound beam inside a liquid phase, a signal processing method for raw velocity data is proposed and used to detect the bubble interface. A conditional averaged liquid phase velocity profile that excludes gas phase data, has shown for the first time the structure of a turbulent boundary layer altered by large buoyant bubbles sliding along the channel wall.
  • Y Murai, S Yoshikawa, S Toda, M Ishikawa, F Yamamoto
    NUCLEAR ENGINEERING AND DESIGN 236 (1) 94 - 106 0029-5493 2006/01 [Refereed][Not invited]
     
    Air-water two-phase flow in helically coiled tubes is investigated experimentally to elucidate the effects of centrifugal acceleration on the flow regime map and the spatial and the temporal flow structure distribution. Three kinds of test tubes with 20 mm inner diameters including a straight tube are used to compare the turbulent flow structure. Superficial velocities up to 6 m/s are tested so that the centrifugal Froude number covers a range from 0 to 3. The interfacial structure is photographed from two directions by a high-speed video system with synchronized measurement of local pressure fluctuations. The results reveal that the flow transition line alters due to centrifugal force acting on the liquid phase in the tube. In particular, the bubbly flow regime is narrowed significantly. The pressure fluctuation amplitude gets large relatively to the average pressure loss as void fraction increases. The frequency spectra of the pressure fluctuation have plural peaks in the case of strong curvature, implying that the periodicity of slugging two-phase flow is collapsed by an internal secondary flow activated inside the liquid phase. Moreover, under large Froude number conditions, the substantial velocity of the gas phase that biases to the inner side of the helical coil is slower than the total superficial velocity because the liquid flow is allowed to pass through the outer side and so resembles a radial stratified flow. (c) 2005 Elsevier B.V. All rights reserved.
  • Yuichi Murai, Jian Wu Qu, Fujio Yamamoto
    Multiphase Science and Technology 18 (2) 175 - 197 0276-1459 2006 [Refereed][Not invited]
     
    Three-dimensional bubble-bubble interaction in quiescent liquid is investigated experimentally using a stereoscopic bubble-tracking technique. An accurate labeling method and a three-dimensional stereo-matching method are applied to the measurement of the three-dimensional centroid for individual bubbles. The velocity vectors of the bubbles are measured by a 3-D four-time-step tracking algorithm and then the relative velocity vectors of two nearest-neighbor bubbles are captured with high statistic reliability. With the measurement data for intermediate Reynolds numbers ranging from 5 to 75, the vertical attraction and the horizontal repulsion are confirmed for Re < 10 as known by a past study based on Navier-Stokes simulation. The new finding of the present measurement is that bubbles of Re > 30 have more repulsive velocity both in the horizontal and the vertical directions because they rise closely. Moreover, the three-dimensional structure of the bubble-bubble interaction is discussed with the data analysis of the interaction vector fields.
  • KONDOH Takayuki, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2006 197 - 198 2006 
    Thermal efficiency of polymer electrolyte fuel cell extremely depends on a water distribution in Gas Diffusion Layer (GDL). Fuel cell model was prepared in order to investigate the water distribution in GDL by ultrasonic techniques. Acoustic impedance of GLD, which is porous plate of carbon, was estimated as bulk model to know approximated value of reflection ratio of ultrasonic echo. We attempted to measure an instantaneous ultrasonic echo that changes by the quantity of the water to detect existing water in GDL.
  • W Cheng, Y Murai, F Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 16 (5) 303 - 308 0955-5986 2005/10 [Refereed][Not invited]
     
    In bubbly two-phase flow, the gas phase and liquid phase have different flow fields. The relative velocity of the two phases depends on the motion characteristic of the bubbles. The mathematical expression for the motion of a small bubble at low Reynolds number is already established. Using the equation, the liquid velocity along the trajectory of the bubble is calculated inversely using the motion equation. Whole field liquid flow structure is also estimated using a spatial and/or temporal interpolation method. This paper proposes an algorithm for estimating the liquid phase flow field from measurement data on bubble motion. In order to verify this principle, Taylor-Green vortex flow and Karman vortex shedding from a square cylinder have been chosen. The results reveal that by combining the inverse analysis and PTV with the spatio-temporal post-processing algorithm one can reconstruct well the carrier phase flow of the gas-liquid two-phase flow. (c) 2005 Published by Elsevier Ltd
  • PIV Measurement of Gas-Liquid Two-Phase Flows
    F.YAMAMOTO, Y.MURAI, T.SASAKI, Y.OISHI, H.FUKUDA
    Proc. 8th FLUCOME 2005 103 - 104 2005/08 [Not refereed][Not invited]
  • Two-Phase PTV for Bubbly Turbulent Boundary Layer and New Findings on Microbubble Drag Reduction Mechanism
    Y.MURAI, Y.OISHI, F.YAMAMOTO
    Proc. 6th Int. Symp. on Particle Image Velocimetry, Pasadena 1 - 7 2005/08 [Refereed][Not invited]
  • Y Murai, H Oiwa, T Sasaki, K Kondou, S Yoshikawa, F Yamamoto
    MEASUREMENT SCIENCE AND TECHNOLOGY 16 (7) 1459 - 1468 0957-0233 2005/07 [Refereed][Not invited]
     
    Air-water two-phase flow in a helically coiled tube is investigated, using backlight imaging tomography to elucidate the effect of centrifugal acceleration on phase distribution and interfacial structure. Superficial velocities up to 6 in s(-1) in 20 min diameter tube are tested. We focused on a slug flow regime in which centrifugal acceleration dominates the flow. The interfacial structure is visualized in six directions using a set of originally designed mirror-mounted water jackets. A temporal expansion image is made from line-sampled images and is used to reconstruct phase distribution through a linear backward projection algorithm. The present topography measurement showed various new features of gas-liquid two-phase flow in a helically coiled tube, such as a wall-covering effect in the case of high superficial velocity.
  • Turbulent Shear Stress Profiles inaHorizontal Bubbly Channel Flow using PTV
    Y.OISHI, Y.MURAI, Y.KODAMA, F.YAMAMOTO
    2nd International Symposium on Seawater Drag Reduction 2005/05 [Refereed][Not invited]
  • Modification of Skin Frictional Drag of Gas-Liquid Two-Phase Flow in a Horizontal Channel
    H.FUKUDA, Y.OISHI, Y. MURAI, Y.KODAMA, F.YAMAMOTO
    2nd International Symposium on Seawater Drag Reduction 2005/05 [Refereed][Not invited]
  • W Cheng, Y Murai, T Sasaki, F Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 16 (1) 35 - 46 0955-5986 2005/03 [Refereed][Not invited]
     
    An image analysis method for measuring bubble velocity fields at high bubble number density is proposed. It is based on computing the cross correlation of bubble images with multiple spatial resolutions, i.e. a recursive cross correlation technique. Comparing several PTV and PIV schemes, it is confirmed that the recursive cross correlation leads to the best measurement results because of the robustness with respect to optical and dynamic characteristics of bubbles. The method is applied successfully to the measurement of bubble motion in bubble plumes accompanying a strong unsteadiness over a wide frequency range. The results reveal that the high frequency fluctuations of bubble velocities grow in the shear layer and near the top surface, while low frequency fluctuations dominate in the middle part of the tank. The characteristic frequency divides the frequency spectrum of the bubble fluctuation intensity into two regions: where there are turbulent behaviors and where there are macroscopic convection patterns in the bubble plumes. (C) 2004 Elsevier Ltd. All rights reserved.
  • Ct-Based visualization of Gas-Liquid Two-Phase flow in helically coiled tubes
    Hiroshi Oiwa, Yuichi Murai, Toshio Sasaki, Shinji Yoshikawa, Fujio Yamamoto
    4th World Congress in Industrial Process Tomography 428 - 433 2005 
    Air-water two-phase flow in a helically coiled tube is investigated using backlight imaging tomography to elucidate the effect of centrifugal acceleration on phase distribution and interfacial structure. Superficial velocities up to 6 m/s in 20mm-diameter tube are tested. We focused on a slug flow regime in which centrifugal acceleration dominates the flow. The interfacial structure is visualized in six directions using a set of originally designed mirror-mounted water jackets. A temporal expansion image is made from line-sampled images, and is used to reconstruct phase distribution through a linear backward projection algorithm. 3D PTV is also carried out to capture a secondary flow induced by the curvature. The present topography measurement showed a V-shaped interface and a wallcovering effect of liquid in the case of high superficial velocity.
  • Masaaki Ashihara, Atsuhide Kitagawa, Yuichi Murai, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 71 (710) 2393 - 2400 0387-5016 2005 [Refereed][Not invited]
     
    Wall-sliding bubbly flow is experimentally investigated using a shallow focus imaging technique. The technique allows to capture the motion of tracer particles inside a thin layer from a wall. Adding digital image processing provides further fine spatial resolution up to 100 ratio of the length of the viewing area to the focused thickness. Bubble-bubble interaction, which is one of dominant phenomena in wall-sliding bubbles, is analyzed with using Particle Tracking Velocimetry applied to both phases. Transition of bubbles' pattern from vertically chained to horizontally clustered arrangement is discussed with the local liquid phase flow structure around individual bubble. The results reveal that the temporally high fluctuation velocity in the liquid phase generates during the transition, and the circulation of bubble-vicinity liquid induces rapid transition of the arrangement.
  • Hiroshi Oiwa, Yuichi Murai, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 71 (706) 1550 - 1557 0387-5016 2005 [Refereed][Not invited]
     
    The fractional drag reduction provided with small bubbles is investigated experimentally using vertical concentric cylinders. The friction reduction ratio is measured using a torque meter mounted on the inner cylinder for a wide range in Reynolds number from wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTV). The present data show around 36% drag reduction in the case of WVF regime at Re = 600 and the reduction maintains until Re=4 000. The friction reduction ratio η defined by the unit void fraction obeyed in a linear relation with inverse values of Froude number, and reached up to 10 in the best case, that implies the highest sensitivity for the drag reduction. The bubble distribution measured in the gap showed a peak near the inner cylinder surface resulting in high local shear stress reduction.
  • Yoshihiko Oishi, Yuichi Murai, Hiroshi Fukuda, Yoshiaki Kodama, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 71 (706) 1542 - 1549 0387-5016 2005 [Refereed][Not invited]
     
    Skin frictional drag of bubbly two-phase mixture in a horizontal turbulent channel is investigated experimentally using a shear stress sensor and a high-speed video camera. We choose non-micro bubbles having a size of 1 to 10 mm intentionally to confirm that the drag reduction still works with relatively large bubbles to the channel height. The measurement results have shown that the drag reduction realized in case of a void fraction higher than a critical value that depends on liquid flow velocity. Also, significant bubble size dependence was found in the region near bubble injector. A synchronized measurement of local shear stress and interfacial structure has newly shown that the instantaneous friction factor decreased in rear part of individual bubble.
  • Qu Jian-wu, Yuichi Murai, Fujio Yamamoto
    JOURNAL OF HYDRODYNAMICS 17 (2) 243 - 251 1001-6058 2005 [Refereed][Not invited]
     
    Bubble-bubble interaction in free rising bubbly flows is experimentally investigated in the present study. The velocity vectors of the bubbles are measured by a stereoscopic bubble-tracking technique and then the relative velocity vectors of two nearest-neighbor bubbles are calculated with high statistical reliability. With the measurement data at Reynolds number ranging from 5 to 75, the vertical attraction and the horizontal repulsion are confirmed for Re < 10 as known by the past study based on Navier-Stokes simulation. The new finding of the present measurement is that the bubbles of Re > 30 have repulsive velocity bothin the horizontal and the vertical directions as those rise closely. Moreover, the three-dimensional structure of the bubble-bubble interaction is discussed with the data analysis of the interaction vector fields.
  • Y Murai, T Sasaki, MA Ishikawa, F Yamamoto
    JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME 127 (1) 117 - 123 0098-2202 2005/01 [Refereed][Not invited]
     
    This paper is concerned with flow visualization and image measurement of bubbly flows around various shapes of cylinders. A coaxial confined double rectangular chamber is constructed in order to provide a wide two-dimensional uniform bubble distribution upstream. The experiment shows that a wide two-phase convection is induced around the obstacle, though such an effect is not observed in research on the single-phase flow around objects. The spatial scale of the two-phase convection depends sensitively on the shape of the obstacle. Dense arrangement of cylinders is also investigated to find the interaction among the convection. The measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by image processing including particle tracking velocimetry, explore the detailed mechanism of generating the convection.
  • YAMAMOTO Fujio, MURAI Yuichi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 25 (2) 255 - 256 0916-4731 2005 
    The analytical algorithm of PIV and PTV has advanced in the last two decades from simple cross correlation method to binary image cross correlation method, Delaunay tessellation method, velocity, gradient tensor method, and recursive cross correlation method. In parallel, useful post-processing schemes for PIV/PTV such as ellipsoidal equation method and inverse analysis method were proposed so that detailed flow structure could be evaluated including pressure field. This paper concerns with such a history of the research and future possibility for further advance of the PIV/PTV.
  • ITOH Tetsuya, MURAI Yuichi, UENO Yasutaka, OIWA Hiroshi, MIYAGI Naoki, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 25 (2) 303 - 304 0916-4731 2005 
    Flow visualization of an inscribed gear pump is carried out to grasp the influence of deformation rate and the rotation of the fluid chamber provided by the two trochoid gears. A transparent model of the pump, which resists friction, is made. A platelet type of light-reflecting tracer particles "Kalliroscope" is adopted and applied to the visualization of flow patterns. Upon taking phase-statistic for the time serial images, the dependence of the flow on Reynolds number is evaluated.
  • OHASHI Junichi, INABA Kazumasa, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 25 (2) 289 - 290 0916-4731 2005 
    An experimental study of air-water two-phase slug flow in a horizontal tube is performed using UVP and high-speed camera. The spatio-temporal velocity profile on the vertical axis is obtained and analyzed using phase-averaging technique. The results show that an upward rising flow is induced inside the liquid slug in the central region of the tube, and remains in the downstream liquid layer below the gas bubble. This implies the liquid slug has a secondary circulation in the cross-section.
  • OISHI Yoshihiko, FUKUDA Hiroshi, MURAI Yuichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 25 (1) 29 - 30 0916-4731 2005 
    Skin frictional drag of the gas-liquid two-phase flow is investigated using silicon oil in a horizontal channel. The silicon oil has three characteristics, i.e. stable interfacial property, high viscosity, and low surface tension in comparison to water. The present study is planned to grasp the skin friction characteristics modified with bubbles in the oil. The measurement and the visulization results show increment of the frictional drag by bubbles because of promotion of the laminar to turbulent flow transition. Bubble shapes changing with the transition is also discussed.
  • Y. Murai, H. Oiwa, Y. Takeda
    14TH INTERNATIONAL COUETTE TAYLOR WORKSHOP 14 143 - 156 1742-6588 2005 [Refereed][Not invited]
     
    Bubble distributions organized in a vertical Taylor-Couette flow are experimentally investigated. Modification of shear stress due to bubbles is measured with a torque sensor installed on the rotating inner cylinder. The wall shear stress decreases as bubbles are injected in all the tested range of Re from 600 to 4500. The drag reduction ratio per void fraction measured in the present experiment, which indicates net gain of the drag reduction, has been evaluated. The gain was more than unity for Re<2000 while it descends negative for Re>4000. The maximum gain achieved was around 10 at Re=600, at which point the bubbles dispersed widely on the inner cylinder surface and effectively restrict momentum exchange of fluid between the two walls. The expansion of Taylor vortices in the vertical direction by the presence of bubbles was confirmed by flow visualization including particle tracking velocimetry. Such bubble behaviours interacting with Taylor vortices are discussed in detail in this paper.
  • J Huang, M Ashihara, Y Murai, Y Kodama, SM Wang, F Yamamoto
    ISTM/2005: 6TH INTERNATIONAL SYMPOSIUM ON TEST AND MEASUREMENT, VOLS 1-9, CONFERENCE PROCEEDINGS 5220 - 5223 2005 [Refereed][Not invited]
     
    Experiments were performed to measure the flow structures of turbulent bubbly flow in a horizontal channel with PTV Streamwise and spanwise components of velocities in the boundary layer were obtained using shallow focal imaging technique which enabled to visualize the motion of bubbles and tracer particles suspended in the near-wall region. Measurements results at three locations downstream a bubble injector showed that the average streamwise velocity in the vicinity of the wall was attenuated by presence of bubbles, implying the reduction of skin frictional resistance.
  • IOP Journal of Physics: Conference Series: Vol.14, 14th International Couette-Taylor Workshop -Sapporo 2005 (2005)
    Institute of Physics UK 2005 [Not refereed][Not invited]
  • Direct measurement of wall-shear stress and flow visualization of bubbles in a horizontal channel
    H.FUKUDA, Y.MURAI, Y.OISHI, M.KOUKAWA, F.YAMAMOTO
    Proc. of International Symposium on Advanced Mechanical Engineering, Between University of Fukui – Pukyong National University 253 - 258 2004/11 [Refereed][Not invited]
  • Shallow Focal Particle Image Velocimetry for Bubbly Flows In a Wall Boundary Layer
    Y.OISHI, M.ISHIKAWA, Y.MURAI, F.YAMAMOTO
    Proc. of 7th Asian Symposium on Visualization CD-ROM, 2B-4,  2004/11 [Refereed][Not invited]
  • A Kitagawa, K Sugiyama, Y Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 30 (10) 1213 - 1234 0301-9322 2004/10 [Refereed][Not invited]
     
    Bubble-bubble interactions in a wall-sliding bubble swarm are investigated experimentally using a particle tracking velocimetry (PTV) technique. Firstly, the drag coefficient of a single wall-sliding bubble is measured, in which the distance between the wall and the bubble interface is much shorter than the average bubble diameter. Secondly, the probability distribution of the nearest bubble around individual bubbles in the bubble swarm is detected in the range from Re = 1 to around 20. Two kinds of statistical sampling techniques are used in order to identify the two-dimensional structure of the bubble-bubble interactions. A local modification of the drag coefficient in the swarm is obtained by calculating the interactive velocity of an individual bubble. Furthermore, the transition of a bubble's arrangement in the swarm is discussed by computing the relative velocity vector. The feature of the interaction patterns obtained by these techniques is classified based on Reynolds number. (C) 2004 Elsevier Ltd. All rights reserved.
  • PIV Measurement of Turbulent Bubbly Two-Phase Flow in a Horizontal Channel
    J.HUANG, M.ASHIHARA, Y.OISHI, Y.MURAI, Y.KODAMA, F.YAMAMOTO
    Proc. of the 4th International Symposium on Measurement Techniques for Multiphase Flows 2004 253 - 259 2004/09 [Refereed][Not invited]
  • Particle Tracking Velocimetry of Turbulent Bubbly Flows in a Horizontal Channel
    Y.MURAI, Y.OISHI, Y.KODAMA, F.YAMAMOTO
    Proc., of the 7th International Congress on Optical Particle Characterization (41) 1 - 5 2004/08 [Refereed][Not invited]
  • Hiroshi Oiwa, Yuichi Murai, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 70 (697) 2286 - 2293 0387-5016 2004 [Refereed][Not invited]
     
    The effective viscosity of bubbly liquid is measured by means of falling sphere method in Stokes drag region. The method can evaluate the influence of bubble's transient deformation around the falling sphere. The relative viscosity, which is defined by the effective viscosity divided by the single-phase viscosity, is directly obtained by the ratio of the terminal falling velocity of the sphere. The results have shown the following points. 1) The relative viscosity at low capillary number agrees to the theoretical formula for the spherical bubble dispersion. 2) The relative viscosity drops down to less than unity as the capillary number gets higher than a critical value. 3) The critical capillary number is around 3.5 for the falling sphere method, and is much larger than that for simple shear flow. 4) The effective viscosity increasing mechanism by bubble's transient deformation is discussed with visualization results and some theoretical works done in the past.
  • 宮城 直樹, 村井 祐一, 宮崎 孝司, 山本 富士夫
    日本機械学会論文集 B 72 (714) 375 - 382 0387-5016 2004 [Refereed][Not invited]
  • Qu Jian-wu, Yuichi Murai, Fujio Yamamoto
    JOURNAL OF HYDRODYNAMICS 16 (6) 756 - 766 1001-6058 2004 [Refereed][Not invited]
     
    A Particle Image Velocimetry (PIV) method based on the image separation and reconstruction with the median filter and triangular Bezier patch was proposed to measure multiple velocity fields from single-camera images in the present study. The method was examined on synthetic PIV images with the Green-Taylor two-phase vortex flows and the test results showed high accuracy and highly correct tracking percent compared with the exact solution. An experiment of the bubbly jet flow was also conducted as a practical demonstration of the present method. As a result, it is confirmed from the simulation image examination and the experimental measurement that the proposed method shows a good performance in the measurement of bubble and particle phases.
  • OISHI Yoshihiko, MURAI Yuichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 24 (1) 125 - 126 0916-4731 2004 
    Particle tracking velocimetry is applied to a bubbly two-phase flow in a horizontal channel to investigate the mechanism of turbulent shear stress reduction using bubbles. We derived three componential stresses to express the phenomenon hidden in the turbulent shear layer and measured them with the PTV data at Re=4×104. It is newly found that the role of a vertically correlated shear stress is important to reduce the total stress effectively.
  • FUKUDA Hiroshi, OISHI Yoshihiko, MURAI Yuichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 24 (1) 111 - 112 0916-4731 2004 
    As a basic study of skin friction reduction using bubbles, the relationship between the skin friction and the bulk void fraction in a horizontal rectangular channel is investigated experimentally for Re=9700. The skin friction is reduced for the void fraction larger than 17% in our test facility, in which the bubble size ranges from 2 to 30mm. The negative correlation between the local skin friction and the local void fraction is confirmed by a time-resolved synchronized measurement, and we also found that the local skin friction decreased in the rear region of large bubbles.
  • MURAI Yuichi, QU Jian Wu, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 24 (1) 173 - 174 0916-4731 2004 
    This paper concerns with experimental measurement of bubble-bubble interaction in a free-rising bubbly flow using three-dimensional Particle Tracking Velocimetry (3-D PTV). An accurate labeling method is employed to measure correctly the center of gravity for individual bubble so that the relative velocity vector in a swarm of bubbles is captured with high statistic reliability. The bubble-bubble interaction is discussed for the range of 5
  • MURAI Yuichi, TODA Shin-ichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2004 259 - 260 2004 
    Helical coil type heat exchanger tubes are used in the evaporator and the superheater of the prototype fast-breeder reactor (FBR) Monju. The present study visualizes the flow pattern of gas-liquid two-phase flow in the helical tubes to clarify the influence of centrifugal acceleration due to the curvature. The three-dimensional interfacial structure is measured using CT from the backlight projection image acquired in six directions at a local section. The results have shown that the interfacial structure became asymmetric in the case of high Ga number, oiwing to combination of gravity and centrifugal acceleration.
  • OISHI Yoshihiko, FUKUDA Hiroshi, MURAI Yuishi, KODAMA Yoshiaki, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2004 243 - 244 2004 
    Experiments were carried out to measure skin friction in a horizontal rectagular channel flow which contains various size of air bubbles. First of all, the relationship between the bubble motion and the temporal fluctuation of local skin friction is investigated experimentally at Re =l.lx10^4, in which approximate bubble size ranges from 3 to 30mm. The negative correlation between the local skin friction and the local void fraction is confirmed by simultaneous measurement of shear stress and interfacial visualization. It became clear that the local skin friction decreased in the rear region of large bubbles. Secondly, particle tracking velocimetry is applied to a bubbly two-phase flow to investigate the mechanism of turbulent shear stress modification. We measured three componential stresses with the PTV data at Re=2.0x10^4 and found that a role of the vertically correlated shear stress was important to reduce the total stress effectively.
  • SASAKI Toshio, KURODA Ichiro, NAGAI Niro, MURAI Yuichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2004 253 - 254 2004 
    Alkaline water electrolysis is the one of technologies of hydrogen production through decomposition of water by an electric power. The present study aims at improvement of hydrogen production in 'water electrolysis from viewpoint of generated bubbles' behavior, which interrupts the electric current between two electrodes. The measurement of electric current and the visualization of bubbly flow are practiced simultaneously to discuss the influence of the two-phase flow structure onto the water electrolysis. The paper describes two experiments on the micro-channel water electrolysis and on the water electrolysis by use of vibrating electrodes.
  • Yuichi Murai, Naoki Miyagi, Koji Miyazaki, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 70 (695) 1754 - 1761 0387-5016 2004 [Refereed][Not invited]
     
    The pumping characteristics and the internal flow structure of an inscribed trochoid gear pump are investigated by means of three-dimensional numerical simulation. Cartesian grid system is employed to calculate the fluid flow while the boundary conditions on rigidly rotating gear surface is expressed with Lagrangian markers. The results reveal that the flow rate and the pressure rise obtained by the pump become the highest at Re=10 when the clearance between the two gears is considered. At lower Re numbers, the shear stress transfer on the gear surface fluctuates significantly resulting into lower performance. For higher Re numbers, backward induced jet flow through the clearance makes the internal flow complicated due to non-uniform centrifugal acceleration.
  • Toshio Sasaki, Masaaki Ishikawa, Yuichi Murai, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 70 (689) 60 - 68 0387-5016 2004 [Refereed][Not invited]
     
    Bubble-driven flow around circular cylinders in a narrow channel is experimentally investigated by means of image processing. The cylinders are settled in the channel with three kinds of arrangement pattern to clarify the difference of the internal two-phase flow structure. Thinning algorithm is applied to the detection of all the bubbles in order to measure the bubble motion in locally high void fraction. Size and spatial distribution of the bubbles are also obtained with the image analysis to discuss the bubble's coalescence/fragmentation due to the collision with the cylinders. The results imply that the rising velocity of the bubble is governed not only by bouncing on the cylinders but also by the liquid phase flow pattern that is sensitively dependent on the gas flow rate and the cylinders' arrangement pattern.
  • F Yamamoto, M Koukawa, Y Murai, JW Qu
    MULTIPHASE, NON-NEWTONIAN AND REACTING FLOWS, VOL 2, PROCEEDINGS 23 - 27 2004 [Refereed][Not invited]
     
    Several novel techniques of PIV including PTV and new results on gas-liquid two-phase flows are introduced in this invited lecture. Instead of Laser-based illumination in PIV, shallow focal imaging technique is available to capture the images of gas-liquid two-phase flows with high image quality and low cost. Multi-velocity field PIV extends conventional PIV to measure simultaneously the flow fields of the liquid phase and gas phase from single-camera images with a high accuracy. The inverse analysis technique makes it possible to estimate carrier liquid phase flow velocities from measurement data of dispersed bubble motion when the dispersion motion is measured with PIV. These techniques have wide practical application in industrial processes, such as micro-bubble drag reduction for ship, etc.
  • F Yamamoto, Y Murai
    RECENT ADVANCES IN FLUID MECHANICS 45 - 50 2004 [Refereed][Not invited]
     
    Several novel techniques of PIV including PTV and new results on gas-liquid two-phase flows are introduced in this invited lecture. Instead of Laser-based illumination in PIV, shallow focal imaging technique is available to capture the images of gas-liquid two-phase flows with high image quality and low cost. Multi-velocity field PIV extends conventional PIV to measure simultaneously the flow fields of the liquid phase and gas phase from single-camera images with a high accuracy. The inverse analysis technique makes it possible to estimate carrier liquid phase flow velocities from measurement data of dispersed bubble motion when the dispersion motion is measured with PIV These techniques have wide practical application in industrial processes, such as micro-bubble drag reduction for ship, etc.
  • Cheng Wen, Yuichi Murai, Toshio Sasaki, Fujio Yamamoto
    JOURNAL OF HYDRODYNAMICS 16 (6) 730 - 736 1001-6058 2004 [Refereed][Not invited]
     
    An inverse analysis algorithm is proposed for estimating liquid phase flow field from measurement data of bubble motion. This kind of technology will be applied in future for various estimation of fluid flow in rivers, lakes, sea surface flow, and also microscopic channel flow as the problem-handling in civil, mechanical, electronic, and chemical engineering. The relationship between the dispersion motion and the carrier phase flow is governed and expressed by the translational motion equation of spherical dispersion. The equation consists of all the force components including inertia, added inertia, drag, lift, pressure gradient force and gravity force. Using this equation enables us to estimate the carrier phase flow structure using only the data of the dispersion motion. Whole field liquid flow structure is also estimated using spatial or temporal interpolation method. In order to verify this principle, the Taylor-Green vortex flow, and the Karman vortex shedding from a square cylinder have been chosen. The results show that the combination of the inverse analysis and Particle Tracking Velocimetry (PTV) with the spatio-temporal post-processing algorithm could reconstruct well the carrier phase flow of the gas-liquid two-phase flow.
  • Shallow Focal Particle Image Velocimetry for Bubbly Flow in the Vicinity of the Wall
    F.YAMAMOTO, Y.MURAI, M. ISHIKAWA, Y.OISHI
    Proc., of the International Symposium 2003 on Advanced Mechanical Engineering 35 - 40 2003/11 [Not refereed][Not invited]
  • Experimental and numerical simulation of three-phase flow in an aeration tank
    Wen Cheng, Xiao-De Zhou, Ce Song, Tao Min, Yuichi Murai, Fujio Yamamoto
    Journal of Hydrodynamics 15 (4) 118 - 123 1001-6058 2003/08 
    Aeration plays an important role in the treatment of activated sludge due to the interactions among bubbles, sewage and activated sludge in an aeration tank. The aeration performance is directly concerned with the efficiency of sewage disposal. So the three-dimensional two-fluid model was established with emphasis on the phase interaction terms in this paper. This model, as an extension of the two-phase flow model, involved the motion laws of three-phases, and was compared with experimental studies. The finite volume method was used in the numerical simulation of gas-liquid two-phase flow and gas-liquid-solid three-phase flow. In order to discuss the influence of gas-phase, liquid-phase and solid-phase motions in an aeration tank on the sewage disposal, three kinds of boundary and initial conditions were adopted. The simulated results of the flow structure show qualitatively good agreement with the experimental data. And the theoretical basis for designing the best aeration tank was discussed according to the simulated results.
  • QU Jianwu, MURAI Yuichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 23 (1) 247 - 250 0916-4731 2003/07/01 
    Bubble-Bubble interaction in a free-rising bubbly flow is measured with three-dimensional Particle Tracking Velocimetry (3-D PTV). The present report mentions the dependency of the interaction pattern on Reynolds number of rising bubble from 5 to 75. With the measurement data, it has been newly found that high Re number bubbles had repulsive motion each other both in horizontal and vertical direction as the distance of bubbles was shortened. The technique of PTV for extracting accurately the 3-D velocity vectors of bubbles is also discussed.
  • Hiroshi Oiwa, Masa-Aki Ishikawa, Yuichi Murai, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 639 - 645 2003 
    Effective viscosity of bubbly two-phase flow is experimentally investigated by means of the falling sphere method. The terminal falling velocity of the sphere is measured by image processing to calculate the relative viscosity of the two-phase flow to the single-phase flow. The measurement results show that the effective viscosity is reduced for a range from 0 to 2% of void fraction as the shearing Weber number increases. This fact implies that the reduction of the effective viscosity is governed by the deformation of the bubbles, and the mechanism is explained by the interruption of the shear stress transfer in the two-phase medium.
  • Masa-Aki Ishikawa, Hiroshi Oiwa, Kosuke Sakai, Yuichi Murai, Shin-Ichi Toda, Kiyoshi Tamayama, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 1453 - 1458 2003 
    In the steam generator of the prototype FBR (Fast Breeder Reactor) in Japan, heat exchange tubes of helical coil type are utilized. The gas-liquid two-phase flows in the helical coil tube have different characteristic from straight tubes due to the effects of centrifugal acceleration in the curved tubes. In our study, the interfacial structure of the gas-liquid two-phase flows in the helical coil tube is visualized to provide the flow pattern map. Simultaneously, the pressure loss and its local fluctuation are measured in order to investigate the dynamic characteristics of the two-phase flow appearing in the helical coil tube. The result reveals that the bubbly flow regime extends and the stratified flow vanishes compared the gas-liquid flow in a horizontal straight tube. Moreover, the slug flow has asymmetric structure due to the effect of centrifugal acceleration. On the contrary the pressure loss is basically not remarkably different from the straight tube except the fact that the pressure has a high fluctuation component.
  • Bubble-Generated Convection in Immiscible Two-Phase Stratified Liquids
    Yuichi Murai, Hassan Abdulmouti, Yasushi Ohno, Masa-Aki Ishikawa, Dae Seok Bae, Fujio Yamamoto
    Proceedings of the ASME Fluids Engineering Division Summer Meeting 1 481 - 486 2003 
    The technique of using a surface flow induced by a bubble plume is proposed to collect the surface-floating oil layer in case of oil-leakage accidents. The fundamental characteristics of the surface flow generation mechanism were presented in the last ASME FED summer meeting -2000. After that, we focus on the actual oil-transportation effect considering the stratified layer of oil on the free surface. In this case, the difference between two fluids in density and viscosity causes a quite unsteady interface motion. The laboratory model experiments and numerical simulation based on Eulerian-Lagrangian model have been carried out in order to investigate the multi-dimensional transportation of the oil due to bubbles. As a referential experiment, the liquid flow pattern of bubble-induced convection in a thermal stratified liquid has been also measured by using PIV in which a color-image processing is combined to measure the temperature field.
  • Takehiro Ido, Hiromasa Shimizu, Yoichi Nakajima, Masa-Aki Ishikawa, Yuichi Murai, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 2257 - 2263 2003 
    Three-dimensional Particle Tracking Velocimetry (3-D PTV) is one of a useful measurement tools to understand complicated structure of flow. This paper concerns with a system of 3-D PTV based on color image processing using a liquid crystal image projector. The merit of the present system is inexpensive setup and needless of complicated procedure for stereo-pair matching of particles since all the process are carried out by single-camera. The accuracy of color-based PTV depends on the image quality and the optical characteristics of color-light scattering on tracer particles. After detailed discussion on these technical problems is mentioned, two kinds of experimental demonstration are shown by a chamber-inside steady flow and a vortex-shedding flow behind rectangular cylinder.
  • Masa-Aki Ashihara, Atsuhide Kitagawa, Masa-Aki Ishikawa, Akihiro Nakashinchi, Yuichi Murai, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 2277 - 2284 2003 
    Bubble-bubble interaction is a quite fundamental issue to understand multiphase flow dynamics and to improve mathematical models of dispersed multiphase flow for higher volume fraction of dispersion. In this study, the bubble-bubble interaction is measured using Particle Tracking Velocimetry (PTV) in various environments. First, bubbles sliding on a vertical wall are measured using 2-D PTV. Second, the free rising bubbles in an unbounded space are measured applying 3-D PTV. Third, the simultaneous measurement for gas and liquid phases in the layer of wall-sliding bubbles is carried out. The measurement data have shown that the average bubble-bubble interaction patterns in the wall-sliding bubbles and in the free rising bubbles were attractive in the vertical direction and repulsive in the horizontal direction. The relation between the carrier phase flow structure and the bubbles' motion is detected to explain the mechanism of the bubble-bubble interaction.
  • Yuichi Murai, Masa-Aki Ishikawa, Toshio Sasaki, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 1429 - 1435 2003 
    This paper concerns with flow visualization and image measurement of bubbly flows around various shapes of cylinders. A coaxial confined double rectangular chamber is constructed in order to provide a wide two-dimensional uniform bubble distribution upstream of the obstacle. The experiment shows that a wide two-phase convection is induced around the obstacle, though such an effect is not observed in research on the single-phase flow around objects. The spatial scale of the two-phase convection depends sensitively on the shape of the obstacle. Dense arrangement of cylinders is also investigated to find the interaction among the convection. The measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by image processing including particle tracking velocimetry (PTV), explore the detailed mechanism of generating the convection.
  • SAKAI Kosuke, MURAI Yuichi, TODA Shinichi, YOSHIKAWA Shinji, ISHIKAWA Masaaki, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2003 293 - 294 2003 
    Helical coil type heat exchanger tubes are used in the evaporator and the superheater of the prototype fast-breeder reactor (FBR) Monju. The present study visualizes the flow pattern of gas-liquid two-phase flow in the helical tubes to clarify the influence of centrifugal acceleration due to the curvature. Flow regime maps for two different curvature radii are obtained. The results reveal that the bubbly flow regime expands and stratified flow regime vanishes compared to the straight horizontal pipe flow owing to the centrifugal force acting on the liquid phase. The bubbly flow regime further expands if the curvature radius increases because of slowdown of the internal secondary flow induced by the centrifugal acceleration.
  • OIWA Hiroshi, MITTA Kazuhiko, ISHIKAWA Masaaki, MURAI Yuichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2003 283 - 284 2003 
    Effective viscosity of liquid containing bubbles is experimentally investigated by means of the rotating coaxial cylinder method. The rotating coaxial cylinder method measures the relative viscosity of the two-phase fluid to the single-phase fluid from the torque for the inner cylinder by a torque meter. In this research, it is made clear that the viscosity characteristics of spherical bubble mixture. The measurement results show that the effective viscosity has a peak on the relationship with shear rate.
  • MURAI Yuichi, ISHIKAWA Masa-aki, ASHIHARA Masa-aki, KINUGAWA Kosuke, YAMAMOTO Fujio
    Transactions of the Visualization Society of Japan 社団法人 可視化情報学会 23 (1) 1 - 8 2003 
    This paper concerns with experimental measurement of bubble-bubble interaction in a free-rising bubbly flow using three-dimensional Particle Tracking Velocimetry (3-D PTV). An accurate labeling method and a ghost-elimination algorithm are employed to measure correctly the center of gravity for individual bubble so that the relative velocity vector in a swarm of bubbles is captured with high statistic reliability. The bubble-bubble interaction is discussed for an intermediate Re number (Re = 10), where horizontal repulsive and vertical attractive motions are detected with the present experiment.
  • CHENG Wen, MURAI Yuichi, ISHIKAWA Masa-aki, YAMAMOTO Fujio
    Transactions of the Visualization Society of Japan The Visualization Society of Japan 23 (11) 107 - 114 1346-5260 2003 
    In bubbly two-phase flow, gas phase and liquid phase have different flow fields, respectively. The relative velocity between two phases depends on the motion characteristic of bubbles. The mathematical expression for the motion of small bubble at low Re number is already established. Using the equation, liquid velocity along the trajectory of the bubble is inversely calculated by the motion equation. Whole field liquid flow structure is also estimated using spatial and/or temporal interpolation method. This paper proposes such an algorithm for estimating liquid phase flow field from measurement data of bubble motion. The frequency response analysis implies high advantage of the inverse analysis from bubble to liquid rather than solid particle to liquid. The applicability of the algorithm is examined with Taylor-Green vortex flow as an analytical test case, and with a bubbly plume as an experimental demonstration.
  • Atsuhide Kitagawa, Kazuyasu Sugiyama, Toshio Sasaki, Yuichi Murai
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 69 (681) 1140 - 1147 0387-5016 2003/01 [Not refereed][Not invited]
     
    In this report, the effects of Reynolds number to the bubble-bubble interaction in a swarm of wall-sliding bubbles are investigated experimentally using PTV (Particle Tracking Velocimetry). Firstly, the drag coefficient of single wall-sliding bubble is measured for four kinds of liquid with different kinematic viscosity and is then compared to single bubble in an infinite liquid. Secondly, the difference of the bubble-bubble interaction among three types of Reynolds numbers, i.e. Re = 1.32, 2.83 and 15.42 is clarified using statistic data such as the interactive velocity vectors, the drag coefficient ratio and the presence frequency of the nearest bubbles. In particular, the discussion is focused on how the vorticity diffusion from the target bubble affects the nearest bubble.
  • T Ido, Y Murai, F Yamamoto
    EXPERIMENTS IN FLUIDS 32 (3) 326 - 336 0723-4864 2002/03 [Refereed][Not invited]
     
    Accurate postprocessing methods are required in order to analyze the detailed flow structures from the scattered data of particle-tracking velocimetry (PTV). In particular, vorticity distributions and stream functions are not reasonably obtained by conventional methods. This paper proposes a new postprocessing algorithm based on ellipsoidal differential equations; this method utilizes data as discrete boundary conditions. The results obtained by the proposed algorithm fully satisfy the equation of continuity and simultaneously correspond well with the raw data. The performance of the algorithm is examined by applying it to two-dimensional vortex flows and isotropic turbulent flows. The results reveal that the present algorithm has the highest accuracy among several conventional methods for detecting vorticity and streamlines.
  • Y Murai, T Ido, F Yamamoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 45 (1) 142 - 149 1340-8054 2002/02 [Refereed][Not invited]
     
    Our previous study confirmed that ellipsoidal differential equations can be used to interpolate particle tracking velocimetry (PTV) measurement results. In the preset study, we deal with extensions of the equations; to time serial processing and to the detection of mismatched vectors. The performance of these algorithms is evaluated by using the flow around a rectangular cylinder and a vortex flow. Furthermore, the actual advantages of utilization of these methods are discussed by applying them to the experimental result of sudden vortex generation due to the collision of a circular cylinder with a flat wall.
  • Murai Yuichi, Ishikawa Masaaki, Ryono Yoshiaki, Toda Shinichi, Endoh Akira, Yamamoto Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2002 7 - 8 2002 
    Heat exchange tubes of helical coil type are utilized in the steam generator of the fast breeder prototype reactor "Monju". The gas-liquid two-phase flow in the tube is affected by the centrifugal acceleration owing to the constant curvature of the tube. This paper presents the flow pattern map obtained by visualization, and the interfacial structure analyzed by stereoscopic image processing for isothermal air-water system. The measurement results have shown that the flow pattern map was widely occupied by slug and plug flows, and the internal liquid slug had asymmetric behavior due to the curvature of the flow.
  • SASAKI Toshio, ISHIKAWA Masaaki, MURAI Yuichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2002 323 - 324 2002 
    Numerical and experimental investigations on bubbly channel flows through closely arranged cylinders have been carried out. This paper concerns with the results of the three-phase simulation using Eulerian-Lagragian model in which the cylinder-bubble interaction model is taken into account. The results show that rising velocity of bubbles decreases due to the bouncing of the bubbles at the cylinder surface, and the characteristic scale of the liquid flow is altered with the arrangement patterns of the cylinders.
  • Atsuhide Kitagawa, Yuichi Murai, Masaaki Ashihara, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 68 (670) 1637 - 1645 0387-5016 2002 [Refereed][Not invited]
     
    In the first report, the two-dimensional bubble-bubble interaction of wall-sliding bubbles is captured by using Particle Tracking Velocimetry. In this report, trial studies to introduce the bubble-bubble interaction into Eulerian-Lagrangian model have been performed. Firstly, the bubble-bubble interaction force vector is estimated by inverse analysis from experimental results. The translational motion equation of a bubble is used to derive the interaction force vector. Secondly, two kinds of interaction models are proposed and applied to the numerical simulation. Comparison between the simulated and experimental results revealed that the introduction of the bubble-bubble interaction model enabled to predict much more accurate structure of sliding bubble motion than previous Eulerian-Lagrangian model.
  • Atsuhide Kitagawa, Masaaki Ashihara, Yuichi Murai, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 68 (668) 1111 - 1118 0387-5016 2002 [Refereed][Not invited]
     
    The bubble-bubble interaction in a swarm of wall-sliding bubbles is experimentally investigated using an image processing measurement. At first, the drag coefficient of a vertically sliding bubble is measured for the range of Reynolds number from 2 to 9. Secondly, the two-dimensional pattern of the bubble-bubble interaction in a layer of wall sliding bubbles is detected by using particle tracking velocimetry (PTV). The evolution of relative coordinates and the relative velocity vectors of the bubbles are clarified by the statistical data analysis. Also, hydrodynamic mechanism of the bubble-bubble interaction is discussed with the present data comparing literatures on twin bubble interactions.
  • Junichi Ohta, Atsushi Shozude, Yuichi Murai, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 68 (668) 1095 - 1103 0387-5016 2002 [Refereed][Not invited]
     
    This paper describes the gas-liquid interface shape and the internal flow field of a liquid bridge that is placed to bridge the cross-section of a horizontal narrow rectangular converging channel made of glass with a gap size of 1.2 mm and a converging angle of 2.97°. Such a liquid bridge is moved to the smaller cross-section by surface tension. Liquid bridge are observed and transported in semi-scale channels and also in gas-liquid separator under a microgravity condition. Thus, it is important to understand the liquid bridge behavior from point of view of semi-scale flows dominated by surface tension. In the present study, a liquid bridge made of ethyl alcohol or mixture of water and ethyl alcohol as the liquid was viewed from the top and the side. (1) The internal flow fields of the liquid bridge in the side view were quantitatively measured by the brightness distribution cross-correlation method, i.e. PIV (Particle Imaging Velocimetry). (2) The gas-liquid interface shape was expressed using Fourier factors, and the feature was clarified. (3) Effects of various parameters on the liquid bridge behavior were examined.
  • A Kitagawa, Y Murai, F Yamamoto
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 27 (12) 2129 - 2153 0301-9322 2001/12 [Refereed][Not invited]
     
    Eulerian-Lagrangian approaches for dispersed multiphase flows can simulate detailed flow structures with a much higher spatial resolution than the Eulerian-Eulerian approaches. However, there are still unsolved problems regarding the calculation method for accurate two-way interaction, especially on the numerical instability due to the dispersion migration through discrete computational grids. Inadequate solvers sometimes produce false velocity fluctuation which makes the simulation unstable. In this paper, a new calculation method for dispersion-to-continuous phase interaction, which is accompanied by spherical dispersion migration, is proposed. The basic principle of the method is the introduction of Lagrangian filtering functions which convert discrete dispersion volume fractions to a spatially differentiable distribution. The performance of linear, Gaussian and sinewave filtering functions is examined by simple benchmark tests and applied to the simulation of dispersion-generated fluctuation. Using the present method, three-dimensional continuous phase flow structures induced by rising spherical bubbles and/or settling solid particles are demonstrated. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • LP Shen, XQ Song, Y Murai, M Iguchi, F Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 12 (3) 191 - 199 0955-5986 2001/06 [Refereed][Not invited]
     
    This paper describes a method for simultaneously measuring the velocities and sizes of falling particles. The measurement method consists of two parts. One is the recognition of the particles from a raw image by an image-processing technique in order to obtain the sizes and positions of the particles, and the other is a measurement technique of Particle Tracking Velocimetry based on fuzzy logic for the falling velocities of particles. The method is examined by a numerical experiment with computer-generated images. The result shows that the present method can be applied on-line for real-time processing of practical measurements. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • Quantitative Understanding of Bubble-Bubble Interaction Dynamics Enabled by Application of Particle Tracking Velocimetry
    Y. Murai, M. Ashihara, M. Ishikawa, A. Kitagawa, F. Yamamoto
    DLR-Mitteilung (3) 1113 - 1120 1434-8462 2001 
    Bubble-bubble interaction is a quite fundamental issue to understand multiphase flow dynamics and to improve mathematical models of dispersed multiphase flow for higher dispersion volume fraction. In this study, two-dimensional particle tracking velocimetry (PTV) is applied to the measurement of wall-sliding bubbles whose motions are governed by the bubble-bubble interaction. Only PTV enables the measurement while PIV based on cross correlation does not determine exact motion of the individual bubbles. Also, the PTV is improved in solving more accurate center of gravity of the bubbles in order to measure the velocity component of the bubble-bubble interaction whose magnitude is an order of a few % as the terminal rising velocity. More than 100,000 velocity vectors of the bubbles are used to calculate the average bubble-bubble interaction pattern in each case during the void fraction and Reynolds number are varied in the range from 0 .00 to 0.15 and 1-100, respectively.
  • Particle Tracking Velocimetry for Dispersions in Multiphase Flows
    F. Yamamoto, Y. Murai, M. Ishikawa
    DLR-Mitteilung (3) 433 - 438 1434-8462 2001 
    PIV and PTV are quite useful tools for measuring dispersed multiphase flows because of possibility of field measurement that provides a lot of information on the dispersion. However, simple application of conventional technique involves several risks of misunderstanding the multiphase flow structure. In this paper, the important differences between tracer particles in single phase flow and dispersions in multiphase flow are discussed through our experience.
  • Y Murai, Y Matsumoto, F Yamamoto
    EXPERIMENTS IN FLUIDS 30 (1) 11 - 21 0723-4864 2001/01 [Refereed][Not invited]
     
    A method for measuring the instantaneous 3-D bubble distribution in bubbly flows is proposed by making use of stereoscopic image processing. The method applies to the case of higher rather than dilute void fractions, because it is based on the following two statistic-based procedures. The first process is to obtain the 2-D distribution of local void fraction from visualized images, where a correlation between the bubble shadow fraction and the projection void fraction is derived by introducing the new idea of overlapping probability of the bubble-images under various conditions. The second process is to reconstruct the 3-D distribution of the local void fraction. In this step, a logical method is proposed in order to obtain the bubble-existence probability function which simultaneously satisfies the two distributions of the two projection void fractions. The present method is applied for instantaneous measurement of the 3-D structure of a bubble plume. The measured results show its particular structure, such as the hollow distribution of the bubbles, and the local spiral structure, which cannot be captured by point-measurement experiments.
  • SASAKI Toshio, MURAI Yuichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 1 271 - 272 2001 
    Bubbles in a particle sedimentation layer has quite irregular and complicated phenomena due to frequent collision between the bubbles and the particles. This paper shows our trial to find out the fundamental characteristics of the bubble behavior using two approaches. One is two dimensional experimental visualization using image analysis to capture the bubble trajectories. Another is numerical simulation considering the bubble-particle collision. These results reveal the particle clustering structure and the bubble's bouncing phenomenon.
  • RYONO Yoshiaki, MURAI Yuichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 1 289 - 290 2001 
    Bubble plume will generate a high-speed and thin surface flow with wide area in sea, lake, and dam. The surface flow has a function to damp the wave motion due to the interaction with rotational motion of the waves. This study concerns with the interaction mechanism based on numerical simulation using the Eulerian-Lagrangian model. This paper shows parametric relationship for the wave damping effect between the wave form and the gas injection condition.
  • Ishikawa Masa-aki, Murai Yuichi, Yamamoto Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 1 195 - 196 2001 
    A lot of PIV algorithm has been dealt with a translation motion. Therefore, error vectors are obtained for strong deformed flows. Nowadays, recursive processes of a cross-correlation PIV and a gradient-based PIV are used as the control of the influence of strong deformed flows. However, these recursive processes do not correspond to strong deformed flows perfectly. In this study, unknown valuables of the gradient-based method including the velocity gradient tensor are employed because of overcoming of strong deformed flows. The performance of a recursive gradient-based method is estimated by a simulation of a Taylor-Green vortex flow.
  • KITAGAWA Atsuhide, ISHIKAWA Masaaki, MURAI Yuichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 1 101 - 102 2001 
    The microscopic flow containing bubbles and solid particles shows complicated behavior but it sways performance of material surface characteristics in fluid machineries and environmental devices. This paper shows simulation technique for the dispersed three-phase flow and the application results for induction flow in the vicinity of a wall with arrangement of rectangular obstacles. Parametric study has been done and revealed that the probability of bubble-capturing in a cavity flow between the obstacles was higher than that of particle.
  • Abdulmouti Hassan, Murai Yuichi, Ohno Yasushi, Yamamoto Fujio
    Transactions of the Visualization Society of Japan 社団法人 可視化情報学会 21 (2) 31 - 37 2001 
    Bubble plume is known as one of transport phenomena which drive a large scale natural convection due to buoyancy of bubbles. Surface flow generated by the bubble plume is utilized for protecting naval systems, rivers, and lakes. In the past, however, the detailed mechanism of the surface flow generation process has not been measured experimentally. This paper reports the characteristics of the surface flow which depends on the gas flow rate, the bubble size, and the internal two-phase flow structure of the bubble plume. The data are obtained by applying particle imaging velocimetry (PIV) to three kinds of visualized images; the first is visualization of the whole field around the bubble plume, the second that of the upper view of the surface flow, and the third that of the surface flow generation region under the free surface. As an additional function of the surface flow, the wave-damping effects are also discussed.
  • KITAGAWA Atsuhide, MURAI Yuichi, YAMAMOTO Fujio
    JAPANESE JOURNAL OF MULTIPHASE FLOW THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 14 (4) 442 - 450 0914-2843 2000/12/15 
    It is known that the Eulerian-Lagrangian approaches for dispersive multiphase flows can simulate detailed flow structures with a much better spatial resolution than the Eulerian-Eulerian approaches. However, there are still unsettled problems regarding the calculation method for two-way interaction. Especially, numerical instability due to the dispersion's migration beyond computational mesh is a serious issue for accurate prediction of flow instability in multiphase systems as well as multiphase turbulent flows. This paper describes revised methods for calculating the continuous phase flow which is induced by the spherical dispersion's migration. Basic principle of the methods are of introduction of template functions which convert discrete mass and momentum sources of the dispersion to spatially continuous sources. Performance of Gaussian and sine wave's template functions are examined and good pridictionability of local two way interaction have been confirmed.
  • Y Murai, Y Matsumoto
    JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME 122 (4) 754 - 760 0098-2202 2000/12 [Refereed][Not invited]
     
    The whole behavior and the mic ro scale flow characteristics of a three-dimensional bubble plume are investigated numerically. The bubble plume drives liquid convection in a rank due to strong local two-phase interaction so that the Eulerian-Lagrangian model is formulated with emphasis on the translational motions of the bubble. In this model, each bubble motion is tracked in a bubbly mixture which is treated as a continuum. The three-dimensional numerical results reveal several particular structures, such as swaying and swirling structures of the bubble plume. These simulated flow structures show qualitatively good agreement with the experimental observations. Furthermore, the detailed behavior in the bubble plume is clarified by various analysis to discuss the dominant factors causing such the strong three-dimensionality.
  • M Ishikawa, Y Murai, F Yamamoto
    MEASUREMENT SCIENCE AND TECHNOLOGY 11 (6) 677 - 684 0957-0233 2000/06 [Refereed][Not invited]
     
    Particle tracking velocimetry (PTV) has recently been recognized as quite an effective engineering research tool for understanding multi-dimensional fluid flow structures. There are, however, still a number of unsettled problems in the practical use of PTV, i.e. the lack of generality of the PTV algorithm for various types of flows and the measurement uncertainty with respect to spatial resolution. The authors have developed a generalized PTV algorithm named the velocity gradient tensor (VGT) method in order to accurately track the tracer particles in a flow held with strong local deformation rates. The performance of the VGT method has already been examined for several simple flow fields, such as linear shearing and Taylor-Green vortex flows. In this paper, the applicability of the VGT method for complicated flows, which include a wide dynamic range in wavenumber, is quantitatively examined by simulation of Rankine vortex flows, Karman vortex-shedding flows around a rectangular cylinder and homogeneous turbulent flows, which are numerically solved by using the unsteady Navier-Stokes equations. The results show that the VGT technique, using only two frames to estimate velocity, performs better than does the four-frame PTV technique and has a remarkably higher tracking performance than those of typical conventional PTV algorithms.
  • Y Murai, A Kitagawa, XQ Song, J Ohta, F Yamamoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 43 (2) 197 - 205 1340-8054 2000/05 [Refereed][Not invited]
     
    The inverse energy cascade in bubbly flow is investigated by a numerical simulation using the Eulerian-Lagrangian model in which the governing equations are formulated with emphasis on the translational motion of bubbles in nonuniform flow. In this paper we are concerned with the validation of the numerical model and various parametric dependencies on the inverse cascade. The calculated results reveal that, 1) continuous growth of the spatial fluctuation scale in a bubble-induced flour is well predicted by the present numerical model and the results have a good analogy with the experimental results which were introduced in our first report, 2) the strong relationship between energy-decaying process and bubble-bubble distance interval is also identified by the present analysis, and 3) the slope of energy-decaying in the high wavenumber region depends on the kinematic viscosity of liquid, and that in the low wavenumber region depends on inhomogeneous buoyancy distribution which changes due to the bubble motion.
  • Y Murai, XQ Song, T Takagi, M Ishikawa, F Yamamoto, J Ohta
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 43 (2) 188 - 196 1340-8054 2000/05 [Refereed][Not invited]
     
    The inverse energy cascade, which is one of the important phenomena to enhance the large-scale flow instability in bubbly flow, is investigated by measuring a local two-phase flow structure driven by buoyant bubbles using particle imaging velocimetry (PIV). In PIV, the flow field of liquid phase is measured by separating an original image to respective phase images using a statistical thresholding method for separating image parameters of bubbles and particles. The present results obtained in the case where the bubble Reynolds number and average void fraction are less than 30 and 1.5%, respectively, confirm the large energy decay with a slope index steeper than - 5/3 in the log-log diagram of energy spectrum in a high wavenumber region. An important relationship between the energy spectrum and the bubble-bubble interval distance is also detected.
  • Y Murai, Y Matsumoto, XQ Song, F Yamamoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 43 (2) 180 - 187 1340-8054 2000/05 [Refereed][Not invited]
     
    The turbulence structure in a rising bubbly flow driven by bubble buoyancy has been analyzed using the Eulerian-Lagrangian model. ii new method of calculating the two-way interaction between the dispersed bubbles and the liquid phase was proposed to accurately simulate the local fluctuations of liquid flow induced by bubble migration. The present two-dimensional simulation revealed that, (1) in the case of the larger bubble, the turbulence structure has the longer wavelength in the vertical direction, and, (2) the wave spectrum of kinetic energy of the liquid phase is sensitive to the average void fraction and the lift force of the bubbles.
  • YAMAMOTO Fujio, MURAI Yuichi
    JAPANESE JOURNAL OF MULTIPHASE FLOW THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 14 (1) 8 - 15 0914-2843 2000/03/15 
    Techniques for measuring velocity distribution in gas-liquid two-phase flow are important to elucidate the mechanisms of the flows in various two-phase systems, and to improve desigining industrial facilities. In this report, we focus on recent advanced techniques based on particle imaging velocimetry (PIV), which is known as a contact-free, multi-dimensional, instantaneous measurement tool. The current problems in applying the PIV to gas-liquid two-phase flows are summarized, and several examples of measured results are shown.
  • Two-Phase Flow Induced by a Bubble Plume in the Vicinity of a Free Surface
    Yuichi Murai, Yasushi Ohno, Abdul M. Hassan, Fujio Yamamoto
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 251 705 - 710 0888-8116 2000 
    This paper is concerned with the fluid dynamic characteristics of a bubble plume, especially focussng on the generation of high speed surface flows at a free surface. Fundamental features of the surface flow are investigated by a numerical analysis based on the Eulerian-Lagrangian model, which is formulated with emphasis on the translational motion of bubbles. The study results in the following conclusions: 1) the effective thickness of the surface flow is much less in case of free surface than in case of non-slip condition, 2) the effective thickness of the surface flow increases when a liquid jet flow is provided instead of the bubble plume, 3) the surface flow involves a wavy fluctuation under the free surface.
  • Shen Liping, Suhara Ohki, Murai Yuichi, Yamamoto Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 20 (1) 201 - 204 0916-4731 2000 
    In this paper, a non-pulsating jet and a pulsating jet are researched experimentally and the experiment data are analyzed with a PTV (Particle Tracking Velocimetry) method. The velocity fields are measured accurately and efficiently with a PTV method based on fuzzy logic although the strong shear and turbulence appear in the jets. Based on the measured velocity fields, the distributions of mean velocity, mean vorticity, shear strain rate and kinetic energy are compared between non-pulsating and pulsating jets in order to analyze the different flow features between the two kinds of flow fields.
  • ISHIKAWA Masa-aki, IDO Takehiro, MURAI Yuichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 20 (79) 365 - 372 0916-4731 2000 
    The authors developed the velocity gradient tensor method (VGT) which was a PTV algorithm for measuring flow field as reported in a previous paper. When the VGT method is used, both the velocity vector and velocity gradient tensor can be obtained at each particle point. The purpose of this study is to propose a new technique for post-processing using the velocity gradient tensor in order to make a rearrangement of velocity vectors at particle points into those at grid points with a high spatial resolution. The per-formance of the processing method is examined by the vortex flow. It is made clear that the present method has high accuracy compared to conventional interpolation methods.
  • MINAMI Tomokazu, MURAI Yuichi, FUJIMOTO Koichi, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2000 461 - 462 2000 
    A peculiar two-phase convection is generated when an object is inserted in a free rising bubbly flow. This paper is concerned with an experimental method to elucidate the bubble behavior around several types of the object based on flow visualization and image processing techniques. Experimental results show the following points; 1) area of single-phase region behind the object depends sensitively on the shape of the object, 2) when many objects are arranged, the single-phase region expands behind the most downstream object.
  • ONO Yasushi, MURAI Yuichi, MASUDA Yoriyasu, NISHIMURA Takuma, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2000 5 - 6 2000 
    Monument-types of savonius windmills designed by combining art sence and windmill technology are produced by the PROD cooperative companies. The "art-oriented" Savonius windmills have been installed in many public sites such as musiums, schools, stations and sight-seeing spots because of its good harmony with natural environment and cities. This report shows a first trial of numerical analysis of flow field around the "art-oriented" windmill. The numerical method is based on incompressible Navier-Stokes equations using Lagrangian markers which express the complex boundary conditions of rotating windmill blades.
  • OHTA Junichi, SUHARA Ohki, MURAI Yuichi, IGUCHI Manabu, MIZUNO Yoshiteru, YAMAMOTO Fujio
    The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2000 99 - 100 2000 
    This paper describes the turbulent flow characteristics of axisymmetric non-pulsating and pulsating jets measured by PIV (Particle Imaging Velocimetry). The PIV measurement is made for a pulsating jet at an amplitude ratio of 0.25,a Strouhal number St of 0.17,and a Reynolds number of 1070. According to the measured velocities, the fluid motions are classified into four quadrant categories, i.e. ejection, outward interaction, sweep, and inward interaction. The contributions of these classes of motion to frequency are analyzed. The present result at St=0.17 and a dimensionless distance of z^^-=4 is different from the previous one measured at St=7.8×(10)^<-4> and z^^-=20. It is clear that the frequency of ejection is dominant and the frequencies of the inward interaction and the sweep become approximately equal for phases just after passing the maximum velocity.
  • Yuichi Murai, Takehiro Ido, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 66 (649) 2265 - 2273 0387-5016 2000 [Refereed][Not invited]
     
    In the first report, improved post-processing algorithms, which rearrange discrete velocity vectors obtained by PTV better into regular grid spaces, were proposed. The present report deals with extensions of the methods to time serial processing and to the detection of mis-matched vectors. The performance of these algorithms are evaluated by using the flow around a rectangular cylinder and a vortex flow. Furthermore, the actual advantages of using these methods are discussed by applying them to the experimental result of sudden vortex generation due to the collision of a circular cylinder with a flat wall. © 2000, The Japan Society of Mechanical Engineers. All rights reserved.
  • Atsuhide Kitagawa, Yuichi Murai, Junichi Ohta, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 66 (642) 323 - 331 0387-5016 2000 [Refereed][Not invited]
     
    This paper is concerned with a numerical method and its application to the prediction for turbulence structure which is induced in three-phase flows containing bubbles and particles. The Eulerian-Lagrangian model for three-phase flows has been constructed since the mathematical validity of the model was confirmed for bubbly two-phase flow in previous papers. Two-and three -dimensional predictions were carried out and provided detailed phenomenological information on three-phase interaction processes. When the bubble and the particle volume fractions were less than 5%, generation of kinetic energy was reduced more in three-phase flow than in two-phase flow, because of decrease in body force spectrum. Especially, the turbulence with long wave length was not strongly grown because of cancelation of meso-scale body force due to local dispersion of the bubbles and the particles. Resultant slope of energy spectrum in high wavenumber region became much calmer than the similar phenomena in bubbly two-phase flow cases.
  • Yuichi Murai, Koichi Fujimoto, Toru Ishiguro, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 66 (646) 1273 - 1280 0387-5016 2000 [Refereed][Not invited]
     
    An experiment showed a quite strong effect of inserting a circular cylinder into a unform rising bubbly flow. Size of the effected zone was more than several times as that of the cylinder. The purpose of present study is to elucidate the mechanism of generating the two-phase convection using a numerical analysis based on Eulerian-Lagrangian model by which the bubble's boundary condition on the cylinder can be treated accurately. The numerical results showed a good agreement with the experimental results and revealed the dependency of the flow on the void fraction, bubble radius, blockage ratio as well as the bubble's bouncing condition on the cylinder surface.
  • M. Ishikawa, Y. Murai, A. Wada, M. Iguchi, K. Okamoto, F. Yamamoto
    Experiments in Fluids 29 (6-6) 519 - 531 0723-4864 2000 [Refereed][Not invited]
     
    Most particle-tracking velocimetry (PTV) algorithms are not suitable for calculating the velocity vectors of a fluid flow subjected to strong deformation, because these algorithms deal only with flows due to translation. Accordingly, it is necessary to develop a novel algorithm applicable to flows subjected to strong deformations such as rotation, shear, expansion and compression. This paper proposes a novel particle tracking algorithm using the velocity gradient tensor (VGT) which can deal with strong deformations and demonstrates that this algorithm is applicable to some basic fluid motions (rigidly rotating flow, Couette flow, and expansion flow). Furthermore, the performance of this algorithm is compared with the binary image cross-correlation method (BICC), the four-consecutive-time-step particle tracking method (4-PTV), and the spring model particle tracking algorithm (SPG) using simulations and experimental data. As a result, it is shown that this novel algorithm is useful and applicable for the highly accurate measurement and analysis of fluid flows subjected to strong deformations.
  • Y. Murai, Y. Matsumoto, F. Yamamoto
    Journal of Visualization 3 (1) 27 - 35 1343-8875 2000 [Refereed][Not invited]
     
    Overall, as well as individual, bubble behavior of a plane bubble plume which is confined by two parallel plates is investigated by means of several qualitative and quantitative flow visualization methods. These include observation, measurement of time-averaged void distribution, surface tufts and particle imaging velocimetry. Several kinds of unstable motion of the bubble convection, which depend on the free surface initial height and on the gas flow rate, are observed. The bubble motion along the bubble plume is precisely measured by an image-processing method which also delivers velocity vectors, number density and size of the bubbles.
  • K Miyazaki, G Chen, F Yamamoto, J Ohta, Y Murai, K Horii
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 19 (4) 194 - 203 0894-1777 1999/08 [Refereed][Not invited]
     
    With a concise review on some basic and novel algorithms and methods for the techniques of particle-imaging velocimetry (PIV), the paper reports an application of the PIV techniques to the investigation of particle motion in a gas-solid two-phase spiral flow in a horizontal tube. Axial velocities of the transported particles are obtained. Some important features of particle motion governing high transportation efficiency of the spiral flow are revealed by investigating probability density distribution of particle locations in a pipe cross-section. (C) 1999 Elsevier Science Inc. All rights reserved.
  • Song, X, F Yamamoto, M Iguchi, Y Murai
    EXPERIMENTS IN FLUIDS 26 (4) 371 - 380 0723-4864 1999/03 [Refereed][Not invited]
     
    A new algorithm of Delaunay Tessellation Particle Tracking Velocimetry (DT-PTV in abbreviation) is proposed for tracking particles in images of a PIV system by making use of the Delaunay tessellation (DT). The algorithm is tested by using numerically simulated particle images. The calculation results based on DT are compared with those obtained by a conventional algorithm of Binary Image Cross-correlation method (BICC). The new algorithm shows higher performance of obtaining more identical particles in two consecutive images correctly with shorter computation time even if the images contain many particles. A further application of DT to elimination of spurious vectors is also discussed.
  • Song, X, F Yamamoto, M Iguchi, H Kato, Y Murai, K Ishii, Y Sasaki
    ISIJ INTERNATIONAL 39 (5) 471 - 476 0915-1559 1999 [Refereed][Not invited]
     
    The number of particles passing through the whole field of interest in a unit lime, referred to as the articles particle number rate, cannot be measured accurately and easily by the conventional methods when the number density of particles is high. However, there are many demands for whole field measurement of the particle number rate in various industrial processes. The purpose of the present investigation is to develop a new method for measuring the particle number rate by introducing PIV (Particle Imaging Velocimetry). In the present work, particles coming out of a hopper, and then falling in air or water were treated. Images of the falling particles were taken by a high speed video camera. Particle velocities were measured by the PIV based on the Binary Image Cross-Correlation Method (BICC), and the particle number rate crossing a plane could be computed from the mean velocity of particles and the number of the particles in the image. The performance of the present method for measuring the particle number rate was evaluated by numerical simulations and experiments. The experimental results showed that the particle number rate of a cloud of particles could be measured with high accuracy by the newly developed methods. The measurement precision of the particle number rate depends on the number of sampling video frames. Several seconds of video frames can yield sufficient precision of the particle number rate. The present research can be applied to on-line measurement of particles in many industrial fields.
  • Eulerian Analysis of Bubbly Two-Phase Flows using CIP Scheme
    Murai,Y, Matsumoto,Y
    Computational Fluid Dynamics Journal 8 26 - 33 1999 [Refereed][Not invited]
  • ABDULMOUTI HASSAN, MURAI YUICHI, OHTA JUNICHI, YAMAMOTO FUJIO
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (1) 239 - 242 0916-4731 1999 
    Bubble curtain is expected to be a new type of oil fence because it can generate a strong and wide surface flow over the bubble generation system. However, the most suitable condition for the bubble generation system has not been investigated. In this work, the surface flow induced by the bubble curtain is measured by particle imagining velocimetry, and the parametric dependency on the gas flow rate, void fraction and bubble size have been made clear. Furthermore, the internal two-phase flow structure in the bubble curtain is discussed with the PIV measurement data.
  • Shinoda Keiji, Ohta Junichi, Murai Yuichi, Yamamoto Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (1) 113 - 114 0916-4731 1999 
    The objective of this study is to apply holography to three-dimensional location measurement of particles. We made experiments using the behind scattering beam type ofF-axis holography with an Ar-Ion Laser. We measured three-dimensional coordinates of particles as follows: Centers of gravity for the particles in a 3-D space were measured by the moment method using a stack of x-y cross-section(slice in the depth direction), y-z cross-section, and x-z cross-section images. The present method is verified. Furthermore, a reconstructed image is showed in a 3-D space.
  • Ido Takehiro, Murai Yuichi, Ohta Junichi, Yamamoto Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (1) 303 - 306 0916-4731 1999 
    Velocity vectors obtained by PTV contain usually mis-matched vectors. In order to estimate the whole flow field structure, the mis-matched vectors should be eliminated exactly. In the present report, a method of mis-matched vector elimination in PTV based on Laplace equation rearrange-ment is proposed. As a result, it is recognized that the present method has good performance by the verification after applying it to two-dimensional vortex flow and Karman vortex flow. Furthermore, it is confirmed to acquire higher performance by using a successive iteration type.
  • ISHIKAWA Masa-aki, MURAI Yuichi, OHTA Junichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (1) 311 - 314 0916-4731 1999 
    We have developed the velocity gradient tensor method (VGT) which is a PTV algorithm. When the VGT method is used at particle points, we can simultaneously get both of the velocity vectors and velocity gradient tensor. It means that physical information can be directly extracted at particle points. The purpose of this study is to propose a new technique of the extraction of physical information at particle points from the velocity gradient tensor. The processing is applied to the vortex flow and PIV-Standard Image, the performance is examined from the precision for extraction of vorticity and stream function.
  • HASSAN ABDULMOUTI, MURAI Yuichi, OHTA Junichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (2) 209 - 210 0916-4731 1999 
    Bubbly flow shows complicated behavior due to a strong dynamic interaction between bubble and vortex motions. A technique for generating a strong surface flow by using a bubble curtain has been proposed by the authors. In the future, bubble curtain is expected to be a new type of oil fence because it can generate a strong and wide surface flow over the bubble generation system. The present paper is concerned with the mechanism of generating the surface flow. Furthermore, the internal two-phase flow structure of the surface flow generation induced by the bubble curtain is discussed using PIV (particle imaging velocimetry) measurement data after separating bubbles and particles from the original images.
  • TAJIMA Carlos, IDO Takehiro, MURAI Yuichi, OHTA Junichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 19 (2) 145 - 148 0916-4731 1999 
    It is well-known that the efficiency of capturing velocity vector in 3-D PTV is much lower than in 2-D PTV due to the problems in particles' occlusion, stereo-matching process, as well as the resolution of the optical hardwares. A new method for particle tracking velocimetry by using a color illumination device with only one camera has been proposed in the present paper. The information of color gradation in the depth direction is employed to determine their 3-D coordinates and velocity components. This report describes the performance of the present method, which is examined by measuring the 3-D flow field of a simple rotating flow.
  • Yuichi Murai, Jun Iwase, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 65 (638) 3366 - 3373 0387-5016 1999 [Refereed][Not invited]
     
    Flow induced by oscillating elastic blades in quiescent liquid is investigated using PIV (particle imaging velocimetry). Theoretical prediction and image-measurement of the bending blade motion ranging from zero to 60 Hz in frequency indicate that is has maximum amplitude in the second order resonance mode owing to large added inertia force. PIV measurement is performed to evaluate the agitation structure around the blade with order of 106 in Reynolds number which is defined using the frequency f blade length L and kinematic viscosity v y Re=fL2/v re than 600 velocity vectors are obtained between two consecutive images by using the BinarizedTmage Cross Correlation algorithm. The present results reveal generation of intermittent convection in the region downstream of the blade, that period is over 10 times as that of oscillating blade. Also, parametirc dependency of induced energy on blade-dimension and forced frequency is shown in this experiment.
  • Y Murai, Y Matsumoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 41 (3) 568 - 574 1340-8054 1998/08 [Refereed][Not invited]
     
    Detailed flow structure of bubbly flours observed in a bubble plume is investigated numerically using the Euler-Lagrange model where the bubbly flow is treated as a continuum and each bubble is tracked in the flow. The governing equations are formulated with emphasis on the translational motion of the bubble in non-uniform unsteady liquid flow. Improvement of the present numerical method is confirmed by comparison with the Eulerian method, and the numerical results are validated by the comparison with the two kinds of experimental results, i.e., global flow pattern visualized by direct-lighting method, and local bubble motion measured by particle imaging velocimetry. In this paper, two-dimensional bubble plume which is confined by two parallel plates is analyzed and the parametric dependency, such as influence of the bubble size distribution and void fraction, on the whole two-phase behavior is clarified and experimental validation is conducted.
  • IDO Takehiro, ISHIKAWA Masa-aki, MURAI Yuichi, YAMAMOTO Fujio
    Transactions of Visualization Society of Japan The Visualization Society of Japan 17 235 - 238 0916-4731 1997/07/01 
    Velocity vectors obtained by PIV are distributed discretely depending on the number density of the tracer particles seeded in the flow. In order to estimate the detailed whole-field flow structure from the data, an estimation algorithm to restore the whole-field flow has been proposed using Laplace Equation and velocity correction potential. The performance of the algorithm was examined for two-dimensional vortex flow. The correct restoration rate was evaluated quantitatively by two-dimensional correlation coefficient for the stream function. The results reveal that the present method is applicable for various conditions of discrete PIV data to predict the whole-field flow structure.
  • PIV measurement of dynamic interaction between oscillating blades and fluid flow inside a bioreactor
    Jun Iwase, Fujio Yamamoto, Yuichi Murai, Manabu Iguchi, Kimiyasu Yasuda, Naoyuki Fujii
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 13 1997 
    This paper is concerned with the interaction of oscillating blade and the fluid flow in a fluidized bed type of bioreactor. The motion properties of blades were investigated through the experimental measurements and theoretical estimation. In the theoretical work, the blade motion was considered with the effect of virtual mass on the oscillating blade. The characteristics of the flow around oscillating blades was investigated with the PIV. The experiment was carried out in some range of the oscillation frequency. A convection waves shed from the blade tip is introduced as a new phenomenon and its behavior is investigated.
  • Numerical and experimental investigations of bursting bubble on free surface
    Toshifumi Yoshikawa, Yuichi Murai, Fujio Yamamoto
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 13 1997 
    The `bursting bubble' phenomenon is observed in various industrial situations such as bioreactors which purify excreta using microbes, heat exchangers for nuclear power plants, and refining system of various metals. For the improvement of safety and controlability of those system, it is required to elucidate its unsteady behavior where large kinetic energy is sometimes generated by strong interaction between rising bubble and upper free surface. The purpose of present investigation is to make apparent the influences of surface tension and viscosity of liquid on the bursting structure by experimental visualization of two free surface motions and numerical simulation using the VOF method. This paper describes mainly the simulation method and the predicted results of bursting bubble structures after showing several experimental results.
  • SONG Xiang-Qun, YAMAMOTO Fujio, IGUCHI Manabu, MURAI Yuichi
    Transactions of Visualization Society of Japan The Visualization Society of Japan 16 19 - 22 0916-4731 1996/11/01 
    In this paper, a new algorithm of particle identification based on Delaunay tessellation is proposed. Delaunay tessellation is a method which connects every scattered nodes to form triangles in either two-dimensional or three-dimensional space. Such a triangulation provides an essential step for spatial analysis of scattered data. Delaunay tessellation can be applied in PIV which deals with the particles in image. A new cross-correlation method for particle identification has been devised and tested by numerical simulation. Good result can be obtained.
  • An investigation of flows of a rotating hollow circular cylinder (When it impulsively starts rotating in a uniform flow)
    Fujio Yamamoto, Manabu Iguchi, Yuichi Murai, Gang Chen, Masahiro Ogawa
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 239 135 - 141 0888-8116 1996 
    The particle imaging velocimetry, or PIV is applied to investigate unsteady flows inside and outside a hollow circular cylinder with impulsively starting to rotate in a uniform flow in order to obtain some fundamental data about the historical force effect and flow features. These flows are visualized by the solid particle tracer technique and analyzed using the PIV based on the two-dimensional binary image cross-correlation method in which three consecutive frames are used to detect positions of particles and to obtain particle velocity vectors. A one-dimensional unsteady model is used to analyze the flow inside the rotating hollow cylinder. For the outside flow, the velocity and pressure in the Navier-Stokes equation are solved based on control volume method in space and an implicit scheme in time. Velocity vectors, streamline patterns, lift and drag are obtained for Re=40 and rotating speed α=1.
  • Artificial void wave propagation in a gas–liquid two-phase horizontal turbulent channel flow
    T. Tanaka, H.J. Park, Y. Tasaka, Y. Murai
    Japanese Jouranl of Mutipahse Flow accepted [Refereed][Not invited]

MISC

  • 田坂 裕司, 大家 広平, 芳田 泰基, 村井 祐一  ながれ : 日本流体力学会誌 = Nagare : journal of Japan Society of Fluid Mechanics  43-  (2)  154  -160  2024/06
  • 大家広平, 芳田泰基, 田坂裕司, 村井祐一  日本バイオレオロジー学会誌(Web)  37-  (2)  2023
  • 大家広平, 芳田泰基, 田坂裕司, 村井祐一  化学工学会年会研究発表講演要旨集(CD-ROM)  88th-  2023
  • 田坂裕司, 芳田泰基, 大家広平, 村井祐一  化学工学会年会研究発表講演要旨集(CD-ROM)  88th-  2023
  • 村井祐一, 村井祐一, 田坂裕司, PARK Hyun Jin, 高野慧, 正信聡太郎  混相流  36-  (3)  2022/09  [Not refereed][Invited]
  • 船体と海水の摩擦抵抗を低減する空気潤滑技術
    村井祐一, 田中泰爾, 堀本康文, 朴 炫珍, 田坂裕司  トライボロジズト, Vol. 67, No. 8, pp.547-554 (2022)  2022/08  [Refereed][Invited]
  • 超音波パルスエコグラフィーによる気泡流のモニタリング
    朴炫珍, 田坂裕司, 村井祐一  可視化情報学会誌, Vol.42, No.163, pp.15-18（2022)  2022/01  [Refereed][Invited]
  • 研究開発の俯瞰ー環境・エネルギー分野2021年版
    村井祐一, ほ  JST研究開発戦略センター年次報告書  2021-  2021/04  [Not refereed][Invited]
  • 非ニュートン性流体の粘弾性は粒子の分散状態に影響されるか？
    芳田泰基, 田坂裕司, 村井祐一  日本機械学会流体工学部門ニューズレター2021  2021-  (4)  2021/04  [Not refereed][Invited]
  • 大家広平, 芳田泰基, 朴げん珍, 田坂裕司, 村井祐一  化学工学会年会研究発表講演要旨集(CD-ROM)  86th-  2021
  • 田中泰爾, 大石義彦, PARK Hyun Jin, 田坂裕司, 村井祐一, 川北千春  日本船舶海洋工学会講演会論文集(CD-ROM)  (32)  2021
  • 超音波による混相流用の流量計の開発
    村井祐一  油空圧技術，日本工業出版  60-  1  -5  2021/01  [Not refereed][Invited]
  • Y. Murai, Y. Tasaka, H.J. Park  The Japanese Society for Experimental Mechanics  20-  87  -94  2020  [Not refereed][Invited]
  • 大石義彦, 中村隼人, 田中泰爾, PARK Hyun Jin, 田坂裕司, 村井祐一, 河合秀樹, 濱田達也, 若生大輔, 川北千春  可視化情報シンポジウム(CD-ROM)  48th-  2020
  • 大石義彦, 藤井夏海, 田中泰爾, PARK Hyun Jin, 田坂裕司, 村井祐一, 濱田達也, 川北千春  日本機械学会流体工学部門講演会講演論文集(CD-ROM)  98th-  2020
  • 田坂裕司, 芳田泰基, 村井祐一  日本機械学会流体工学部門講演会講演論文集(CD-ROM)  98th-  2020
  • 大家広平, 芳田泰基, PARK Hyun Jin, 田坂裕司, 村井祐一  日本機械学会流体工学部門講演会講演論文集(CD-ROM)  98th-  2020
  • 芳田泰基, 田坂裕司, 村井祐一  日本機械学会流体工学部門講演会講演論文集(CD-ROM)  98th-  2020
  • Ultrasonic Monitoring of Gas-liquid Two-phase Turbulent Flows
    Y. Murai, Y. Tasaka, H.J. Park  Japanese Visualization Information  39-  11  -16  2019/09  [Not refereed][Invited]
  • 田坂裕司, 芳田泰基, 村井祐一  ながれ  38-  (4)  283‐290  2019/08/25  [Not refereed][Not invited]
  • 田坂 裕司, 芳田 泰基, 村井 祐一  ながれ : 日本流体力学会誌 = Nagare : journal of Japan Society of Fluid Mechanics  38-  (4)  283  -290  2019/08
  • 熊谷一郎, 熊谷一郎, 村井祐一, 川北千春, 濱田達也  混相流シンポジウム講演論文集(Web)  2019-  2019
  • 田坂裕司, 芳田泰基, 村井祐一  混相流シンポジウム講演論文集(Web)  2019-  ROMBUNNO.F232_0026 (WEB ONLY)  2019  [Not refereed][Not invited]
  • 芳田泰基, 田坂裕司, PARK H. J, 村井祐一  日本レオロジー学会年会講演予稿集  45th-  75‐76  2018/05/17  [Not refereed][Not invited]
  • 芳田泰基, 田坂裕司, PARK Hyun Jin, 村井祐一  混相流シンポジウム講演論文集(Web)  2018-  WEB ONLY  2018  [Not refereed][Not invited]
  • LI Ruixue, YOSHIDA Taiki, HITOMI Jumpei, SAWADA Koki, PARK Hyun-Jin, TASAKA Yuji, MURAI Yuichi, FISCHER Stéphane  The Proceedings of the Fluids engineering conference  2018-  (0)  OS4  -1  2018  [Not refereed][Not invited]
     
    <p>We studied a measurement using UVP (Ultrasonic Velocity Profiler) for the milk products flowing in pipe line; here, whole milk, low-fat milk and water-coffee cream were employed as samples of the milk products. Those milk products all include fat as emulsion. Although the diameter of fat particles is much smaller than suitable size of UVP tracer particles, UVP can measure velocity in the whole milk in short distance; Sufficiently large number of fat particles in the milk, however, also cause strong attenuation of ultrasonic wave. Wedge-shape wave guide was thus designed to have sufficiently strong ultrasonic wave with considering measurement in thick stainless-steel pipes, where further strong attenuation is expected.</p>
  • TASAKA Yuji, YOSHIDA Taiki, PARK Hyun-Jin, MURAI Yuichi  The Proceedings of the Fluids engineering conference  2018-  (0)  OS4  -2  2018  [Not refereed][Not invited]
     
    <p>We have developed novel rheometry using a cylindrical vessel in periodic oscillations and ultrasonic velocimetry (UVP) to overcome critical problems in conventional torque-type rheometry caused by influences of shear-banding, slips, non-homogeneous distribution of rheological properties, etc. The rheometry, termed "ultrasonic spinning rheometry", evaluates quantitatively different rheological properties, representative "local" Newtonian viscosity, shear modulus, linear viscoelasticity, through fundamental mechanical relations utilizing spatio-temporal velocity information measured by UVP. In this report, basic concept of the rheometry and its applicability and measurement limitations are summarized. Further, application of frequency-domain algorithm on linear viscoelastic analysis was described in detail.</p>
  • Development of a laser Doppler wall shear stress sensor for bubbly two-phase flow measurement
    Y.Oishi, S. Onuma, H. Kawai, H.J. Park, Y. Tasaka, Y.Murai  Japan-U.S. Seminar on Two-Phase Flow Dynamics 2017  117  -120  2017/06  [Refereed][Not invited]
  • 岩佐耕節, 芳田泰基, PARK Hyun Jin, 田坂裕司, 村井祐一  混相流シンポジウム講演論文集(CD-ROM)  2017-  ROMBUNNO.D113  2017  [Not refereed][Not invited]
  • 村井 祐一, 田坂 裕司  化学工学  80-  (8)  468  -471  2016/08
  • 田坂 裕司, 白鳥 貴久, 芳田 泰基, 村井 祐一  可視化情報学会誌 = Journal of the Visualization Society of Japan  36-  (142)  103  -107,図巻頭1p  2016/07  [Not refereed][Not invited]
  • 芳田泰基, 田坂裕司, 村井祐一  可視化情報学会誌  36-  (Suppl.1(CD-ROM))  ROMBUNNO.D112  2016/07  [Not refereed][Not invited]
  • 渡村友昭, 北川石英, 田坂裕司, 村井祐一, 杉山和靖  混相流シンポジウム講演論文集(CD-ROM)  2016-  ROMBUNNO.B122  2016  [Not refereed][Not invited]
  • 田坂裕司, 芳田泰基, 村井祐一  混相流シンポジウム講演論文集(CD-ROM)  2016-  ROMBUNNO.B115  2016  [Not refereed][Not invited]
  • OISHI Yoshihiko, PARK Hyun Jin, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2015-  "0601  -1"-"0601-2"  2015/11/07  
    We carried out large-scale towing tank experiments as an open flow system to elucidate spatial development of quasi-uniformly injected bubbles. Measurement results by a shear stress sensor indicated drag reduction by injecting bubbles into turbulent boundary layer developing on a flat plate, and visualized pictures showed spontaneous development of quasi-periodic distribution of bubbles at the corresponding parameters.
  • YOKOYAMA Soya, MURAI Yuichi, TASAKA Yuji, VLASKAMP Jop, DENISSENKO Peter, THOMAS Peter J.  Fluids engineering conference ...  2015-  "1702  -1"-"1702-2"  2015/11/07  
    Influence of background rotation on the behavior of a bubble plume in a tank is investigated experimentally, purposing a flow control for large LNG container subject to the Earth rotation. We used the rotating tank facility in University of Warwick, and found a single air-chimney stabilized in the case of point-source of air injection. In contrast, the line-source bubble injection resists to the chimney formation and keeps planer curtain like structure. We also found eccentric oscillation of bubble plume in the disk-source type of injection.
  • MURAI Yuichi, TASAKA Yuji, OHKUBO Jumpei, OISHI Yoshihiko, TAKEUCHI Tomoaki  Fluids engineering conference ...  2015-  "1703  -1"-"1703-2"  2015/11/07  
    Wavy concentrations of mist flow are observed in a horizontal pipeline as Reynolds number falls into transition regime between laminar and turbulent states. We analyzed numerically the behavior of the mist using synthetic gas phase flow structure which models turbulent puffs, and succeeded in simulating the wavy passages.
  • OSUKA Susumu, KOBAYASHI Hiroaki, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Mechanical Engineering Congress, Japan  2015-  "J0510102  -1"-"J0510102-5"  2015/09/13  
    The use of Savonius type wind turbines is effective for wind from variable directions as a result of its omnidirectivity. In the past research, the wake structure of Savonius turbine has been researched for enhancing the performance. Also, it has been reported that interaction of flow among multiple Savonius turbines realized extra power generation in particular configurations. As a further advanced approach, twisted Savonius type wind turbines is now ongoing issue while being spread rapidly. However, aerodynamic characterization of the wake structure of a twisted Savonius turbines has not been established yet. The interaction of multiple twisted Savonius turbines by applying the near wake field is one of the possibilities of increasing efficiency. In this study, we focused on the vertical movement of blades of twisted Savonius turbines, and obtained the velocity vector fields on vertical cross section of the wake behind of a twisted Savonius turbine by particle tracking velocimetry (PTV) technique, and interpolated the vector fields by means of Laplace equation rearrangement (LER). As a result, it was revealed that the flow field have vertical component definitely, and flow field itself moves to flow direction with turbine rotating. In addition, vortex shedding was occurred in the vertical cross section wake structure.
  • TSUKAHARA Takahiro, OGATA Masayuki, KUMAGAI Ichiro, OISHI Yoshihiko, SAKAMAKI Haruki, MURAI Yuichi  Mechanical Engineering Congress, Japan  2015-  "J0510105  -1"-"J0510105-4"  2015/09/13  
    We have invented a novel bubble generator with a vented hydrofoil for ship drag reduction. The hydrofoil has an air outlet on the top surface, and small air bubbles are generated by the negative pressure above the hydrofoil as the device moves forward. In order to understand the relationship between the local shear stress and the local projection void fraction under the ship hull, towing tank (100m) experiments using a 4m-long model ship made by transparent acrylic resin were conducted at Hiroshima University. The void imaging data obtained by a high-speed video camera revealed that the characteristics of the entrained bubbles (bubble size, bubble volume flux, etc.) depend on the towing velocity, angle of attack, and the arrangement of the vented hydrofoil. A large amount of air was introduced by this device when the hydrofoil was mounted at the non-inverted position with the angle of attack from 10 to 15 deg. On the other hand, the local drag reduction rate of the inverted hydrofoil setting was higher than that of the non-inverted one.
  • KOBAYASHI Hiroaki, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, WINDHAB Erich  Mechanical Engineering Congress, Japan  2015-  "J0510104  -1"-"J0510104-5"  2015/09/13  
    To understand the flow characteristics around a wing in viscoelastic fluids, velocity vector field of 0.50 wt% polyacrylamide (PAA) solution around a wing was obtained with particle image velocimetry (PIV). According to the velocity vector data, flow separation was vanished in lateral part of wing surface in PAA solution. To identify the mechanism of this phenomenon, streamline, shear rate, and shear strain was derived. And then first normal stress difference and shear stress were estimated by means of Kelvin-Voigt model and Lodge and Meissner formula. According to normal stress difference distribution, on the lateral part of upper surface of wing, first normal stress difference (Ni) was enhanced. First normal stress difference implies the stress balance between stress along streamline direction and stress along normal direction of streamline. Therefore, it fulfills important role in deformation such as stretching and compression. In case of positive Ni, flow element is stretched along streamline direction and compressed along normal direction of streamline. And rebound pressure against the deformation works in opposite direction of this deformation; compressing pressure in streamline direction and stretching pressure in normal direction of streamline. Thereby in this case, flow is suppressed to upper surface of wing by stretching pressure in vertical direction of streamline, which results in vanishment of flow separation.
  • Diffusion behavior of oil mist in a horizontal pipe flow
    T.Takeuchi, Y.Oishi, I.Kumagai, Y.Tasaka, Y.Murai  Proc. 9th International Symspoium on Measurement Techniques for Multiphase Flow  165  -166  2015/09  [Refereed][Not invited]
  • Void imaging in two-phase flow for ship drag reduction
    T.Tsukahara, M.Ogata, I.Kumagai, H.Sakamaki, Y.Oishi, Y.Murai  Proc. 9th International Symspoium on Measurement Techniques for Multiphase Flow  65  -66  2015/09  [Not refereed][Not invited]
  • Ultrasonic measurement of gas bubbles advecting under a ship bottom for investigating drag reduction performance
    H-J. Park, Y.Oishi, Y.Tasaka, Y.Murai  Proc. ASME-JSME-KSME Joint Fluids Engineering Conference  2015/07  [Refereed][Not invited]
  • Flow visualization around bubble generating hydrofoils
    T.Tsukahara, M.Ogata, Y.Oishi, H.Sakamaki, Y.Murai, I.Kumagai  Proc. ASME-JSME-KSME Joint Fluids Engineering Conference  2015/07  [Refereed][Not invited]
  • Color particle image velocimetry improved by decomposition of RGB distribution integrated in depth direction
    Y.Murai, N.Yonezawa, Y.Oishi, Y.Tasaka, T.Yumoto  Proc. ASME-JSME-KSME Joint Fluids Engineering Conference  2015/07  [Refereed][Not invited]
  • Mechanisms of toroidal - spiral transitions in Taylor-Couette system with microbubble injection
    B. van Ruymbeke, Y.Murai, Y.Tasaka, Y.Oishi, C.Gabullet, C.Colin, N.Latrache, T.Ozaki  Proc. 19th International Couette-Taylor Workshop at Cottbus-Senftenberg  72  -73  2015/07  [Refereed][Not invited]
  • 田坂裕司, 木村拓史, RAPBERGER Richard, 大石義彦, 村井祐一, 芳田泰基  混相流シンポジウム講演論文集(CD-ROM)  2015-  ROMBUNNO.C142  2015  [Not refereed][Not invited]
  • 村井 祐一, 小林 一道  混相流  28-  (4)  483  -486  2014/12
  • MURAI Yuichi  Journal of the Japan Institute of Energy  93-  (11)  1038  -1043  2014/11  
    Injection of small bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. In the case of small bubbles, drag reduction occurs with their unique dynamic characteristics in turbulence. One of them is highlighted by significant viscoelasticity in clustered microbubbles that appears in the high-enstrophy regions in turbulence. Also, deformability of small bubbles subject to strong shear suppresses surrounding turbulence so that friction decreases. Based on these physics, several applications to ship drag reduction are introduced, which realized about 10% fuel saving with small bubbles as they were suitably supplied on the ship hulls.
  • Ultrasonic measurement of bubble motions in a wall boundary layer.
    H-J.PARK, Y.OISHI, Y.TASAKA, Y.MURAI  2014 HU-SNU Symposium on Mechanical and Aerospace Engineering.  53  2014/11  [Not refereed][Not invited]
  • OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi, TOHGE Yukihiro  Fluids engineering conference ...  2014-  "0215  -1"-"0215-2"  2014/10/25  
    Bubble cluster is naturally formed during the bubbles' advection in horizontal turbulent channel flows. The phenomenon cannot be mathematically modeled by the linear sum of bubble-liquid interaction, but it should be assessed with multi-scale modeling in densely dispersed bubbly flow. A series of original geometrical definitions have been proposed to characterize the bubble cluster behavior, such as statistical uniformity of spatial bubble arrangement and bubbles' radial distribution function. From the data analysis, we have found that bubble clustering remains potentially in any flow conditions including the case of large bubble-size deviation
  • TSUKAHARA Takahiro, HAMA Noriko, KUMAGAI Ichiro, OGATA Masayuki, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2014-  "0213  -1"-"0213-2"  2014/10/25  
    Aimed at reducing power consumption by subsurface aerator, a gyromill type bubble generator was developed based on bubble generating hydrofoils for ship drag reduction. This device utilizes the negative pressure region generated on the surface of the rotating hydrofoil, which enables the subsurface aeration without air compression. Small air bubbles with the diameter from sub-mm to mm order were released from an air outlet of the rotating hydrofoil. In this study, the bubble generation process and the performance of the bubble generator were investigated. In particular, the influence of rotating speed, water depth, and angle of attack on the bubble volume flow rate were reported.
  • TASAKA Yuji, NAKASHIMA Takahiro, MURAI Yuichi, OISHI Yoshihiko  Fluids engineering conference ...  2014-  "0520  -1"-"0520-2"  2014/10/25  
    We dealt with the wake of a permeable disk with different solidity as a simple model to investigate an essence of wake of a wind turbine. Velocity defect at the center of the streamwise cross section of the wake was measured at each downstream position by hot-wire anemometer to characterize the wake. Variations of the velocity defect obey power law in far wake regions and the variation of the corresponding index numbers with respect to the solidity has the local maximum. It suggests there is a regime change on the vortex structure. We also investigated the wake of a model of two-blade turbine. Here the variations of the velocity defect show different tendency in far wake regions.
  • MURAI Yuichi, KITAURA Hidekazu, TASAKA Yuji, KINO Seiji  Fluids engineering conference ...  2014-  "0205  -1"-"0205-2"  2014/10/25  
    Based on experimental findings in laboratory scale about the density destratification process by a bubble plume, a set of numerical simulations have been carried out. Eulerian-Lagrangian bubbly flow model equations are applied for the bubble plume to numerically replay the process in 2D and 3D geometries. Enhancement of the destratification by repetitive bubble injection (RBI) has been confirmed in 2D simulation, which is realized by wavy transport of density currents along horizontal density interfaces. The same effect in a real 3D geometry of a dam lake has been partly observed. However, complexity of the flow domain makes it obscure, implying farther study required to intensity the function of the RBI-based destratification.
  • YOKOYAMA Soya, MURAI Yuichi, OISHI Yoshihiko, TASAKA Yuji, TAKEDA Yasushi  Mechanical Engineering Congress, Japan  2014-  "J0540301  -1"-"J0540301-4"  2014/09/07  
    As the number of wind turbines is increasing rapidly in the world, those pose a serious problem which rare birds impact turbine blades. It is getting more important to collect data for objective assessment of current birdstrike's problem. The authors try to offer optical base diagnosis system which detects flying birds in wind farms. The system composes of two units bird detection and bird species identification. In detection part, frame-differential method is applied to extract only birds from moving objects. In classification part, we estimate flapping frequency of birds from consecutive images so that the length scale of the bird can be estimated from aero-biological correlation. The present system allows a single-view monitoring to measure the distance of flying birds from the camera without employing stereoscopic photographing.
  • KOBAYASHI Hiroaki, ODA Tomoro, OISHI Yoshihiko, Tasaka Yuji, Murai Yuichi  Mechanical Engineering Congress, Japan  2014-  "J0510202  -1"-"J0510202-5"  2014/09/07  
    As a new technique for visualizing three-dimensional air flow fields, multi-layer coloring of smoke-wire technique is proposed. This method is composed of four processes. (1)The specific plane of the flow is illuminated by sheet light to detect z coordinate. (2)Sheet light is shifted in z direction to detect z coordinates of the other plane of the flow and this process is repeated for whole layer of z coordinates in the measurement area. (3)To express z coordinates, the recorded gray-scaled image is colored differently in each layer. (4)The colored images are integrated into one image. In this integrated colorful image, we can understand the three-dimensional structure of the flow by the position and the color of the smoke. By means of this technique, three-dimensional flow field around a twisted Savonius wind turbine was visualized. According to the visualized image, in the convex side of the blade, the separation of attached flow is suppressed and in the concave side of the blade, with the move of the flow to +z direction, the angle of outlet flow is increased. Thereby it was concluded that twisted Savonius wind turbine is inferior in the drag characteristics and superior in the lift characteristics. This result suggests that the twisted Savonius turbines have advantages in conditions of the higher tip speed ratio, where the lift force has priority.
  • ODA Tomoro, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Mechanical Engineering Congress, Japan  2014-  "J0510201  -1"-"J0510201-5"  2014/09/07  
    Needs of pressure field measurement by combining experimental results obtained by PIV and governing equations are rapidly increasing. On the other hand, PTV is one of PIV techniques, whose advantages are Lagrangian particle tracking and higher measurement resolution than PIV. In this study, we proposed the new methodology to estimate pressure distribution by using irregularly-distributed pressure gradient data. The first computing step is to calculate numerical integration to obtain pressure on the grids from scattered data points. The second step is to interpolate pressure on the scattered points by using Shepard scheme. The pressure distribution is converged by iterating these two steps. We chose Taylor-Green vortex flow as a model flow to validate the computation results. The difference of boundary conditions caused the different converged pressure value, so that it is difficult to estimate pressure with high quantitative accuracy, but it is possible to discuss the relative pressure distribution qualitatively. In addition we researched the effects of grid space, the number of referenced data and wave number for computing results by using correlation coefficient. We indicated that this method is particularly available in case of low wave number flow with high resolution grid in spite of the number of referenced data.
  • Y. Tasaka, T. Watamura, H.J. Park, Y. Murai, Y. Oishi  Chemical engineering of Japan  78-  593  -596  2014/09  [Not refereed][Invited]
  • Deformation Characteristics of a Dispersing Element in an Oscillating Shear Flow
    H.YAMAUCHI, P.DENISSENKO, Y.MURAI, Y.MIYAGISHIMA, I.KUMAGAI, Y.OISHI, Y.TASAKA  ASME 2014 4th JOINT US-EUROPEAN FLUIDS ENGINEERING DIVISION SUMMER MEETING  2014/08  [Not refereed][Not invited]
  • Model-free rheometry based on unsteady velocity profile analysis
    T.SHIRATORI, Y.OISHI, Y.TASAKA, Y.MURAI, Y.TAKEDA  9th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering  97  -100  2014/08  [Refereed][Not invited]
  • Viscoelastic response of flow driven by a moving permeable disk
    T.NAKASHIMA, T.SHIRATORI, Y.OISHI, Y.TASAKA, Y.MURAI, Y.TAKEDA, E.J.WINDHAB  9th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering  69  -72  2014/08  [Refereed][Not invited]
  • Ultrasound detection of wall-travelling bubbles for diagnosis of drag reduction
    H-J.PARK, H.KAYUKAWA, Y.OISHI, Y.TASAKA, Y.MURAI  9th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering  53  -56  2014/08  [Refereed][Not invited]
  • Bubble deformation responses in oscillatory shear at high dynamic capillary numbers
    Y.MURAI, T.KIMURA, H.YAMAUCHI, Y.TASAKA, Y.OISHI  16th International Symposium on Flow Visualization 2014 Okinawa  ISFV16-1037-  1  -13  2014/06  [Refereed][Not invited]
  • NAKASHIMA Takahiro, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2013-  "0623  -01"-"0623-02"  2013/11/09  
    Wake flow behind a permeable disk is visualized, which phenomenologically simulates far-wake aerodynamic characteristics of a horizontal axis wind turbine. Smoke wire method and hot wire anemometer are used to evaluate periodic fluctuation of the flow in the region from 5 to 25 times the disk diameter downstream to the permeable disk. The experiment has shown that there causes a significant three-dimensional spiral-like vortical fluctuation that long persists downstream within the wake. Decrease in solidity of the permeable disk, thus, increase in aerodynamic permeability of the wind turbine, lowers Strouhal number for primary frequency of the velocity fluctuation and decreases the time averaged velocity and turbulence intensity of wake behind the disk.
  • PARK Hyun Jin, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2013-  "0312  -01"-"0312-04"  2013/11/09  
    In the frictional drag reduction using bubbles, we proposed a periodic bubble injection technique to improve the performance and the new technique improved the performance 66% in Re 2200 at a horizontal channel flow. In this paper, the void fraction fluctuation in higher Reynolds number condition is investigated by visualization. The uncontrolled fluctuation of the void fraction fluctuation doesn't have any specific frequency, however the artificial fluctuation of void fraction maintain its frequency in streamwise. We indicate that it is possible to control density and shape of a swarm of bubbles by controlling the injection frequency and gas volume.
  • MURAI Yuichi, KAYUKAWA Hirohide, KITAURA Hidekazu, OISHI Yoshihiko, TASAKA Yuji, KINO Seiji  Fluids engineering conference ...  2013-  "0202  -01"-"0202-02"  2013/11/09  
    Experimental and numerical flow visualizations on density destratification process provided by a bubble plume in horizontally long environment are presented. The experiment has shown that the initial density stratification can be broken broadly by creation of intermediate density layer inside turbulent bubble plume since the intermediate layer naturally induce density current in the horizontal direction. The process has been simulated in a 2-D rectangular tank, which further revealed that oscillation of bubble plume promoted the current. 3-D simulation applied for a dam has shown activation of destratification by the intermediate density layer regardless of geometry of the dam.
  • YAMAUCHI Hideaki, MIYAGISHIMA Yoshihito, KUMAGAI Ichiro, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2013-  "0201  -01"-"0201-02"  2013/11/09  
    The aim of this study is to clarify the large deformation characteristics of a droplet in oscillating shear flow. Oscillating shear flow is generated between parallel plates which move opposite directions with sinusoidal waveform with motor sliders. A droplet is set between two plates and it receives shear stress from the plates. A deformed droplet is illuminated by green-laser sheet light and its shape is recorded by a high-speed video camera. The experimental results show that time variations of deformation parameter D have viscoelastic response to strain. Phase advance of maximum deformation parameter to strain θ_ was described as a function of maximum capillary number Ca_.
  • KAYUKAWA Hirohide, Park Hyun Jin, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2013-  "0214  -01"-"0214-02"  2013/11/09  
    In the frictional drag reduction by using bubbles, fluctuations of void fraction take an important role to enhance the effect. We have investigated the mechanisms on formation of bubble clusters that provide the large fluctuation. The objective of this study is establishing a new measurement system of passing interval of bubbles with ultrasonic wave in order to find out the property of void fluctuation. We conducted synchronous measurement of ultrasonic pulse emission and video camera recording of bubble images in a horizontal bubbly channel flow. The present technique provided reasonable results on the passing interval in comparison with the estimates from the images. Probability distributions of the passing bubbles obtained at three different points in the downstream represent influence of bubble coalescence.
  • KUMAGAI Ichiro, SAKAMAKI Haruki, OZAKI Yutaka, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2013-  "0215  -01"-"0215-02"  2013/11/09  
    In order to reduce the energy necessary for supplying air bubbles for ship drag reduction, we propose two types of devices for bubble generators using hydrofoils. One is the winged air induction pipe (WAIP), which has an angled hydrofoil with an air introducer, utilizes the low-pressure region produced above the hydrofoil as the ship moves forward, which drives atmospheric air into water. Another type of bubble generator is the device that consists of hydrofoils with air holes provided on their surface. Small bubbles are generated from the air holes when the hydrofoil moves to create low pressure region around the air hole. In this presentation we describe the principles of bubble generation processes based on a simple fluid dynamic theory and on towing tank experiments. We also report the optimization of the hydrofoil bubble generators using flaps.
  • HIRAI Kenta, KUMAGAI Ichiro, OGATA Masayuki, MURAI Yuichi, KURITA Kei  Fluids engineering conference ...  2013-  "0205  -01"-"0205-02"  2013/11/09  
    We report a series of experimental study on the flow behavior of a buoyant jet in a non-Newtonian fluid with gel beads. A viscous fluid is supplied from a nozzle at a constant volume flux in the gel beads layer. The hydrogel beads are deformable and the volume fraction of the interstitial fluids is about 15%. In our experiments, we identify at least three types of fluid flow: homogeneous permeable flow, pulsating flow, and localized continuous flow. The flow behavior depends on the injection flow rate, the rheological properties of the mixture, and the volume fraction of the interstitial fluid. Our experimental model explains the origin of the intermittent nature of multiphase flow observed in food industries and magma transport in nature.
  • Characterization of Viscoelasticity from Complex Flows with Shear and Extension
    T.SHIRATORI, Y.OISHI, Y.TASAKA, Y. MURAI  The 12th International Symposium on Fluid Control, Measurement and Visualization (FLCOME2013)  OS8-04-2, USB  2013/11  [Refereed][Not invited]
  • Yuji Tasaka, Kazuto Igaki, Ichiro Kumagai, Yuichi Murai  Jets, wakes and separated flows : proceedings of International Conference on Jets, Wakes and Separated Flows, ICJWSF  2013-  (4)  "1064  -1"-"1064-5"  2013/09/16  
    A novel technique to measure temperature and velocity fields in liquid metal layer was proposed to understand localized fluid motions accompanied by heat transfer. A thin fluid layer of liquid gallium was adopted to simplify the fluid motion, and a sheet of thermo-chromic liquid crystal paint and ultrasonic velocity profiling provided visualization of temperature and velocity fields. Flows due to injection of small blobs of liquid gallium into the liquid gallium layer were investigated to demonstrate and evaluate the measurement technique and the setup.
  • ODA Tomoro, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Mechanical Engineering Congress, Japan  2013-  "J054012  -1"-"J054012-5"  2013/09/08  
    Vertical-axis wind turbines (VAWTs) have been attracting attention in recent years because of omnidirectivity. Namely they can start to rotate by wind from all directions. Moreover it has been reported that interactive flow field of two VAWTs increases the total output power. However an arrangement of two VAWTs loses omnidirectivity that is the great advantage of a VAWT. In order to reduce the disadvantage, we focused on controlling wake of a VAWT by modifying its blade setting angle. We made some small turbine models which have different blade setting angle (θ= 0,3,6 and 9), and conducted a visualization experiment in wind tunnel. After that velocity distribution was calculated by particle image velocimetry (PIV). As a result it was clarified that in the case of θ=6 and 9°, velocity defect area was reduced. This result indicates that it is possible to install VAWTs in further close proximity. Moreover it was revealed that in the case of θ= 0 and 3°, vortex shedding occurred at the forward blade, but in case of θ=6 and 9°, it did not. In this experiment we conclude that change of wake structure by modification of blade setting angle spreads variations of arrangements without performance degradation of the turbine which is installed in downstream.
  • MURAI Yuichi, ODA Tomoro, OISHI Yoshihiko, TASAKA Yuji  National Symposium on Power and Energy Systems  2013-  (18)  29  -30  2013/06/19  
    As for fundamental understanding of densely arranged vertical axis wind turbines expected in future, wind tunnel model experiments are carried out to find out the aerodynamic interaction between two wind turbines With PIV measurement of time-dependent flow field, the interaction mechanism is deduced, which is classified into near-field interaction due to pressure-field coupling, and far-field interaction due to mean velocity distribution Savonius and Darrieus turbines are compared, and we have found different interaction mechanism between them Savonius turbine, which rotates at tip-speed ration less than unity, produces a dynamic pressure fluctuation to enhance the near-field interaction In contrast, two Darrieus turbines interact with shear layer released by rotating blade at high tip-speed ratio
  • KUMAGAI Ichiro, SAKAMAKI Haruki, TASAKA Yuji, OISHI Yoshihiko, MURAI Yuichi  National Symposium on Power and Energy Systems  2013-  (18)  187  -188  2013/06/19  
    We have investigated flow behaviour around a moving hydrofoil beneath an air-water interface in order to optimize the hydrofoil facility of bubble generation for drag reduction of ship. Experimental results of flow visualization show that the deformation characteristics of the air-water interface depend on the occurrence of the flow separation over the hydrofoil. The attachment of the flaps to the hydrofoils causes significant deformation of the air-water interface in the downstream, which induces wave breaking and results effective bubble generation. On the other hand, we could not observe the effective bubble generation by the vortex generators because the magnitude of the free surface deformation becomes small due to turbulent flow.
  • MIYAGISHIMA Yoshihito, Denisenco Petr, KUMAGAI Ichiro, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2012-  215  -216  2012/11/16  
    Non-equilibrium deformation of a droplet in an oscillatory shear flow was investigated. Two plates which are set parallel to each other are moved as opposite phase oscillation to make the shear flow. The flow behavior was visualized by High Speed Video-camera with laser light sheet. Silicone oil of 10,000 cSt and Glycerin aqueous solution are used as continuous phase and dispersed phase respectively. We measured the deformation parameters such as D and diot flow direction of a droplet and have compared the non-equilibrium deformation response with the equilibrium one to obtain the relationship between the deformation of a droplet and the transient shear flow.
  • MURAI Yuichi, KUMAGAI Ichiro, TASAKA Yuji, OISHI Yoshihiko, OYABU Koji  Fluids engineering conference ...  2012-  223  -224  2012/11/16  
    Flow induced by a moving object beneath free surface is investigated by means of EFD-CFD hybrid analysis. Free surface profiles from experimental images are coupled with 2-D Navier-Stokes simulation in order to obtain the internal liquid flow structure that takes place during two-way interaction between free surface motion and the wake structure of the objects. Targeting of two types of objects, a circular cylinder and an elliptic hydrofoil, their drag and lift coefficients being modified by the presence of free surface have been estimated and discussed.
  • KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji, WATAMURA Tomoaki, KURITA Kei  Fluids engineering conference ...  2012-  213  -214  2012/11/16  
    We have conducted laboratory experiments on spatio-temporal evolution of laminar plumes in a deformable gel beads layer. A thin experimental tank is filled with the mixture of deformable gei beads and a sugar syrup solution as the interstitial fluid. The buoyant plumes are generated by injection of a viscous fluid from a thin slit. When we injected a buoyant fluid, a gravitational instability like Rayleigh-Taylor instability occurs; Then the flow is localized and buoyant plumes are generated. The plume flow is relatively continuous at the source region, however, flow instability occurs along the plume axis and the pulsating flow is developed.
  • OISHI Yoshihiko, TOHGE Yukihiro, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2012-  221  -222  2012/11/16  
    Experimental investigation on drag reduction by air bubble injection is carried out to elucidate the influence of bubble clustering in a horizontal rectangular channel. Silicone oil is used as working fluid so that experimental uncertainty due to contamination is removed particular for the clustering phenomenon. Bubbles formed chained arrangement in the streamwise direction on laminar flow states, and disperse isotropically on turbulent states. Such a bubble clustering behavior is analyzed quantitatively with image processing to obtain probability distribution of the nearest bubbles.
  • TAKEUCHI Tomoaki, TORIUMI Ryoichi, TASAKA Yuji, Kumagai Ichiro, Murai Yuichi  Fluids engineering conference ...  2012-  237  -238  2012/11/16  
    The statistical measurement of particles behavior in horizontal cylindrical pipe has been conducted by means of PTV technique. The results suggest that with increasing the gas velocity the behavior of particles shifts from creep or short range saltation to long range saltation or continuous suspension. It is also indicated that the force acting on the particles in boundary layer plays an important role to determine the flow regime of particles.
  • OISHI Yoshihiko, MURAI Yuichi, TASAKA Yuji  北海道支部講演会講演概要集  2012-  (51)  85  -86  2012/10/20
  • MURAI Yuichi, TASAKA Yuji, OISHI Yoshihiko, TAKAHASHI Yoshiaki  北海道支部講演会講演概要集  2012-  (51)  97  -98  2012/10/20
  • Sato Keiya, Kumagai Ichiro, Oishi Yoshihiko, Tasaka Yuji, Murai Yuichi  北海道支部講演会講演概要集  2012-  (51)  95  -96  2012/10/20
  • MURAI Yuichi  Journal of the Japan Society of Mechanical Engineers  115-  (1127)  688  -690  2012/10/05
  • YUMOTO Takeaki, WATAMURA Tomoaki, TASAKA Yuji, KUMAGAI Ichiro, MURAI Yuichi  Mechanical Engineering Congress, Japan  2012-  "J055022  -1"-"J055022-5"  2012/09/09  
    3-D PIV applying tomographic reconstruction technique of smoke concentration pattern in a 3-D measurement volume has adopted for large scale airflows. The measurement system is composed of a liquid-crystal display projector for the color-coded volumetric illumination and a single camera for capturing RGB color intensity components of misty tracers. The 3-D tracer concentration pattern is obtained from the RGB color intensity components. In this paper, we applied Color PIV to large measurement volume in airflows. Measurement volume is unrestricted by the spatial resolution of a camera because smoke concentration profiles are used for reconstruction. For the application of this technique, flow fields of elliptical vortex ring and wake of a delta wing were measured. Flow fields reconstructed by our technique were appropriately measured even if flow patterns were quite different in each layer.
  • KUMAGAI Ichiro, Davaille Anne, KURITA Kei, MURAI Yuichi  Mechanical Engineering Congress, Japan  2012-  "J055014  -1"-"J055014-4"  2012/09/09  
    Fluid dynamics of thermo-chemical plumes in viscous fluids was investigated. Flow pattern, temperature and compositional fields were quantitatively visualized by microcapsules of thermo chromic liquid crystals, fluorescent dye, and a laser light sheet. The behavior of thermo-chemical plumes depends on the initial buoyancy ratio B_0, which is the ratio of the stabilizing chemical buoyancy to the destabilizing thermal buoyancy at the onset of convection, and also on time. For intermediate B_0, the interplay between the thermal and compositional effects generates complicated behaviors. Because all hot plumes cool by thermal diffusion as they rise, a chemically composite thermal plume eventually attain a level of neutral buoyancy, and a secondary plume is generated from the tip of the chemical dome, then at which it begins to collapse. The thermo-chemical blob is refueled after the falling process because heat flux of the heater is constant in our experiment. Here we describe the oscillation behavior of the thermo-chemical plumes for the intermediate B_o based on the results of the heat flux by the thermo-chemical plumes.
  • MURAI Yuichi, IDO Takehiro  Mechanical Engineering Congress, Japan  2012-  "J055021  -1"-"J055021-5"  2012/09/09  
    How richly can we derive flow information from sparsely discrete velocity vector data? The problem is encountered at many situations in flow measurement from microbiological to meteorological scales. Conventional local interpolations such as Shepard and spline techniques provide visually smooth vector field, however, their spatial and temporal derivatives are mostly useless for quantitative assessment of the flow structure. Ellipsoidal interpolation developed by the authors overcome the problem since it enables global interpolation that deals velocity vector data as randomly distributed discrete boundary conditions. In this paper, reconsideration of the mathematical background and recent applications to fluid dynamics researches are reported.
  • Oyabu Koji, Kumagai Ichiro, Tasaka Yuji, Murai Yuichi  北海道支部講演会講演概要集  2011-  (50)  95  -96  2011/10/01
  • TAKESHIMA Kotaro, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2011-  (50)  99  -100  2011/10/01
  • YUMOTO Takeaki, WATAMURA Tomoaki, TASAKA Yuji, MURAI Yuichi  北海道支部講演会講演概要集  2011-  (50)  97  -98  2011/10/01
  • NAKASHIMA Takahiro, TAKESHIMA Kotaro, TASAKA Yuji, MURAI Yuichi  北海道支部講演会講演概要集  2011-  (50)  109  -110  2011/10/01
  • SHIRATORI Takahisa, KUMAGAI Ichiro, TASAKA Yuji, MURAI Yuichi  北海道支部講演会講演概要集  2011-  (50)  105  -106  2011/10/01
  • AIKAWA Yuki, SHIRATORI Takahisa, TASAKA Yuji, MURAI Yuichi, MIYAGI Naoki  Mechanical Engineering Congress, Japan  2011-  "J055015  -1"-"J055015-5"  2011/09/11  
    Flow inside a Trochoid gear pump for microbubble fluids is visualized using Kalliroscope flakes to grasp the effect of adding microbubbles on the flow structure. Upon taking phase-statistics for the time serial images, average brightness and standard deviation varying with Reynolds number are obtained. At Re = 2000, the turbulence occurs due to jets of counter flow in enclosed unit. The turbulence is, however, alleviated by the addition of microbubbles: turbulent component is weakened by adding microbubbles. Critical Reynolds number for turbulent flow transition is increased by adding microbubbles. It indicates that the pump volume efficiency may be improved by keeping the laminar flow state in the enclosed unit even at higher Reynolds numbers than in single phase conditions.
  • KUMAGAI Ichiro, OYABU Koji, KUSHIDA Takafumi, MURAI Yuichi, TASAKA Yuji, TAKAHASHI Yoshiaki  National Symposium on Power and Energy Systems  2011-  (16)  191  -192  2011/06/22  
    We have invented a new power-saving device for ship drag reduction by microbubbles in order to reduce the CO_2 emissions from ships. The new device, which consists of angled hydrofoils with air introducers, has been installed on a coaster and 〜10% net power saving is achieved. This device utilizes a low-pressure region produced above the hydrofoil as the ship moves forward, which drives the atmospheric air into the water. Here we present its principal and optimization of the device based on laboratory experiments on hydrofoils moving beneath a free surface. Especially, the flow behaviors of the entrainment through the interface and bubble formation process are discussed.
  • MURAI Yuichi, TANAKA Daiki, SHIGETOMI Akinari, TAKESHIMA Kotaro, TASAKA Yuji, XIN Wen  National Symposium on Power and Energy Systems  2011-  (16)  355  -358  2011/06/22  
    Flow noise of wind turbines is already on serious stage that starts to restrict the spread of wind power generation. For vertical axis wind turbines for urban area, the noise-causing mechanism is more important to be clarified because of near-distance impact to people. We measured flow fields around several models of blades using particle image velocimetry and hot wire velocimetry in order to evaluate the type and the source of flow noise in the case of vertical axis wind turbines.
  • MURAI Yuichi, NARABAYASHI Tadashi, WATANABE Masao  Japanese journal of multiphase flow  25-  (1)  60  -63  2011/03/15
  • SAKURAI Kosuke, TASAKA Yuji, MURAI Yuichi, SCHMITT Philippe, FISCHER Stephane, PALLARES Anne  北海道支部講演会講演概要集  2010-  (49)  91  -92  2010/11/07
  • TANAKA Daiki, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2010-  53  -54  2010/10/29  
    A blade which has fluctuating pitch angle influences on the air field around itself. The purpose of this study is to investigate unsteady aerodynamics which acts on a turning plate by Particle Image Velocimetry (PIV). This technique makes us possible to access the flow field around the fluctuating pitch angle of the blade. Comparison of the flow fields between a turning flat plate and non-turning flat plate indicates drastic differences even in the same attack angle; i.e. flow direction, appearance of the flow separation, width of the wake and so on. Phase averaged velocity distribution in a range of the angle shows periodic generation of vortex.
  • Nambu Yuichi, Tasaka Yuji, Murai Yuichi  Fluids engineering conference ...  2010-  571  -572  2010/10/29  
    Vortex ring impacting a solid boundary in a rotating fluid has been visualized by dye to know the effect of rotation to its circumferential instability. Decrease in centerline ejection velocity has been observed due to the existence of background rotation. However, the number of waves of vortex ring in rotating fluid which are generated when it impacts a solid wall was almost same as that of without any background rotation. This result shows the number of waves of vortex ring which can be estimated by the initial condition is reproduced when it impacts a solid boundary even though the effect of rotation exists in the flow.
  • TASAKA Yuji, MURAI Yuichi, IIMA Makoto  Fluids engineering conference ...  2010-  521  -522  2010/10/29  
    We investigate a surface shape and a flow field around the surface in the temporally irregular surface switching of rotating fluids to clarify the mechanism of the phenomenon. Interface detection and estimation of two-dimensional velocity field from spatio-temporal velocity distributions successfully represent an elliptic surface shape and flow mixing due to the rotating surface.
  • SHIRATORI Takahisa, TASAKA Yuji, MURAI Yuihci  Fluids engineering conference ...  2010-  465  -466  2010/10/29  
    Velocity vector field of 1.0 wt% polyacrylamide (PAA) solution around a falling sphere was obtained with particle image velocimetry (PIV). Paths of fluid particles were calculated according to the obtained velocity field. Particles near the falling sphere are driven to downward at first. After that the particles come back to almost initial position while forming negative wake. Vibrations of the particles were observed before the particles settle terminal position. The amplitude, center and frequency of the vibration depend on the distance between the fluid particle and the path of the sphere.
  • Murai Yuichi  Fluids engineering conference ...  2010-  601  -602  2010/10/29  
    An effective utilization of non-flow-tracing particles such as small bubbles in liquid and small soap bubble in air is proposed as an extension of application in PIV and PTV. The method is composed of inverse analysis of the equation of transverse motion and interpolation of scattered velocity data in spatio-temporal domain, which enables unsteady flow field to be reconstructed.
  • 武田 靖, 田坂 裕司, 村井 祐一  化学工学 = Chemical engineering  74-  (8)  381  -384  2010/08/05
  • Ooasa Kouichi, Souma Sadahiro, Tasaka Yuji, Murai Yuichi  National Symposium on Power and Energy Systems  2010-  (15)  1  -2  2010/06/20  
    Interaction between Savonius turbine and Darrius turbine as they rotate coaxially in uniform inflow is investigated experimentally. When they are arranged closely with the tip-radius ratio of 2.5, Darrius-to-Savonius interaction is examined by measuring the change of rotational speed relative to isolated Savonius turbine in uniform flow. Its inverse, i.e. Savonius-to-Darrius interaction, is evaluated by lift force of the blade subjected to flow around Savonius turbine measured by PIV. The results have shown that the Savonius-to-Darrius interaction provides improvement of Darrius turbine performance at middle range of tip-speed ratio. Therefore, hybridization of these two turbines is concluded to be suitable not only in artistic designing for realizing compact design, but also in the aspect of fluid dynamics.
  • Jamshidnia Hamidreza, Takeda Yasushi, Murai Yuichi  日本流体力学会年会講演論文集  2010-  171  -171  2010
  • Murai Yuichi, Tasaka Yuji  日本流体力学会年会講演論文集  2010-  159  -159  2010  
    We have found a significant promotion of turbulent frictional drag reduction when the void fraction of bubbles injected into the boundary layer involves temporal fluctuation. The fluctuation is induced naturally when the two-phase shear flow develops spatially in the streamwise direction. By providing the fluctuation artificially with repetitive bubble injection (RBI-technique), we have succeeded in expanding the drag reducible range regarding mean void fraction. The experimental facts demonstrating the fluctuation's effect and simplified mathematical description are reported here.
  • TANAKA Daiki, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2009-  (48)  63  -64  2009/11/28
  • NAMBU Yuichi, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, VLASKAMP Jozef, THOMAS Peter J.  北海道支部講演会講演概要集  2009-  (48)  65  -66  2009/11/28
  • OYAMA Kazuya, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2009-  (48)  61  -62  2009/11/28
  • SHIGETOMI Akinari, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  北海道支部講演会講演概要集  2009-  (48)  57  -58  2009/11/28
  • SAKURAI Kousuke, OYAMA Kazuya, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  Fluids engineering conference ...  2009-  427  -428  2009/11/06  
    In order to obtain effective viscosity in bubbly liquid, which changes with transient bubble deformation, spatio-temporal velocity distributions of transient shear flows in a rotating cylinder is measured by using Ultrasonic Velocity Profiling (UVP) synchronizing of bubble deformation measurement. For Silicone oil of 1000 cSt as a test liquid, velocity distribution during spinning up has been found to be different from the liquid without bubbles. We have compared the circumferential acceleration of liquid with time serial images of bubble deformation to reach the conclusion that the maximal stretched bubbles the strongest drive the shear flow contrastively to the conventional equilibrium deformation theory of effective viscosity.
  • Jamshidnia Hamidreza, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2009-  523  -524  2009/11/06  
    Effect of an intermediate standing baffle on the flow structure in a rectangular open channel has been studied by using Ultrasonic Doppler Velocimetry (UVP). Distributions of time-averaged on-axis velocity profiles at different streamwise positions indicate the flow structure of the uprising flow at the upstream of baffle and specifically vortex shedding at the downstream of the baffle. Importantly, comparison of space-dependent power spectra of upstream and downstream sections of the baffle indicates the existence of some peak structures near the baffle's edge for downstream sections which are corresponding to the periodic nature of flow concentrated mainly near the baffle's edge in the spatio-temporal velocity distribution. Such peak structures could not be observed for the upstream sections. For downstream sections mainly the existence of peak values in the space distribution of two frequency modes near the baffle's edge could be confirmed which can be attributed to the vortex shedding.
  • TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, IIMA Makoto  Fluids engineering conference ...  2009-  519  -520  2009/11/06  
    Temporally irregular switching of rotating free surface is investigated by means of ultrasonic velocity profiling, UVP. Two methods, Doppler method and echo method, are complementarily used to detect position of the free surface together with spatio-temporal velocity distribution. Horizontal cross section of the free surface shape is estimated from the obtained interface variation.
  • KUMAGAI Ichiro, NAKAMURA Naoya, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan  29-  (2)  9  -10  2009/10/15
  • MURAI Yuichi  可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan  29-  (2)  11  -12  2009/10/15
  • MURAI Yuichi, KUMAGAI Ichiro, TASAKA Yuji, TAKEDA Yasushi, TAKAHASHI Yoshiaki  National Symposium on Power and Energy Systems  2009-  (14)  95  -96  2009/06/28  
    Installation of hydrofoils to ship wetted surface enables bubble generation to be realized with power consumption much lower than conventional bubble generators. With help of this principle, net effect of frictional drag reduction for ships can be improved. We have already obtained around 10% net power-saving efficiency for a cargo ferry throughout about a half year. The power-saving has a large potential to be improved more by considering multiphase fluid dynamics in terms of the hydrofoil-water-air triple interaction. In this paper, the basic principle of the bubble generation and the trial parametric studies implemented by numerical and experimental visualizations are reported.
  • 繁富 啓詞, 村井 祐一, 田坂 裕司, 武田 靖  動力・エネルギー技術の最前線講演論文集 : シンポジウム  2009-  (14)  45  -46  2009/06/28  
    Experiments were conducted to explore the effects of the mutual interaction between two widely spaced Savonius rotors within a wind tunnel. The number of revolution was investigated for two different velocity and conditions, being under small friction and high friction with revolution control. The optimum set of the parameter was found to be u= 4.0 m/s, (x, y) = (2.0D, 0.5D) with two rotors rotating in the same direction under small friction, and the number of revolution of them became 9.1% larger than that of the single rotor. In contrast, increase of revolution was not observed with u= 5.0 m/s under the condition of revolution control and high friction. This result shows that the mutual interference of two Savonius rotors depends on the relation between wake structure and tip speed ratio.
  • MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi, OHTA Shoko, SHIGETOMI Akinari, HINATSU Munehiko  Japanese journal of multiphase flow  23-  (1)  21  -28  2009/03/15
  • OHTA Shoko, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan  28-  (2)  95  -96  2008/09/15
  • OISHI Yoshihiko, MURAI Yuichi  可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan  28-  (2)  15  -16  2008/09/15
  • TAKAHASHI Junpei, YANO Kanako, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, YANAGISAWA Takatoshi, YAMAGISHI Yasuko  可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan  28-  (2)  59  -60  2008/09/15
  • MURAI Yuichi  Journal of Japan Society of Fluid Mechanics  27-  (4)  321  -328  2008/08/25  
    Bubbly flows have multi-dimensional structure that involves plural phenomena with different wavelengths. PIV-particle image velocimetry, therefore, is suitably applied for measuring their spatial organization. In addition, kinematics of bubble and PIV scheme correlate mathematically since they deal with motion of dispersions mixed in flow. Namely, development of PIV system and study on bubbly flows progress in parallel to contribute to each other. In this paper, several experimental demonstrations of PIV application are reported, which features the characteristics of bubbly flow.
  • OISHI Yoshihiko, BREND Mark A., THOMAS Peter J., MURAI Yuichi, TAKEDA Yasushi  可視化情報学会誌. Suppl.  28-  (1)  19  -20  2008/07/01
  • KANDA Tetsushi, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl.  28-  (1)  17  -18  2008/07/01
  • MURAI Yuichi, YAMADA Miyuki  可視化情報学会誌. Suppl.  28-  (1)  459  -460  2008/07/01
  • YOSHIMOTO Takahiro, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl.  28-  (1)  413  -414  2008/07/01
  • KANDA Tetsushi, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi, TEZUKA Hideaki, MORI Michitsugu  National Symposium on Power and Energy Systems  2008-  (13)  405  -406  2008/06/18  
    The present study aims at developing a 3-D trajectory measurement system for birds (in particular endangered species, e.g. raptorial) flying around wind turbines as a part of its complete system to be applied for prevention from bird strike. The method is based on stereoscopic photography which is similar to 3-D particle tracking velocimetry. For stabilizing the bird-image detection performance, time differential technique is proposed and examined considering the influences of hour and weather. All tests are conducted at Hokkaido University firm. For the demonstration purpose, 3-D trajectories of crows above the firm are obtained and shown in order to assess the effectiveness of stereoscopic photography.
  • OHTA Shoko, SHIGETOMI Akinari, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, HINATSU Munehiko, KODAMA Yoshiaki  National Symposium on Power and Energy Systems  2008-  (13)  227  -228  2008/06/18  
    Friction drag accounts for 80 % of the total drag for large ships, and hence microbubble drag reduction is expected as one of the most feasible ways to reduce it because of less environmental impact. The demonstration experiment using 127m-ship is carried out and its turbulent boundary layer is measured by UVP for the first time. This report mainly describes the measurement method of seawater velocity profiles beneath the ship and some typical results on the influences of bubbles on their statistic values.
  • MURAI Yuichi  National Symposium on Power and Energy Systems  2008-  (13)  163  -164  2008/06/18  
    Savonius turbine is known as a wind power generator that is driven by drag force acting on two cylindrical blades. The drag is, however, insufficient to maximize the power efficiency because of interaction of fluid around the pair of blades. In order to see and evaluate detailed flow structure, PIV technique is used and applied to Navier-Stokes equations for obtaining pressure field information. With the results, the use of low-pressure region on convex surface of the blade is suggested so that lift force reinforces the torque as drag is lacked. Moreover, streamwise and lateral oscillatory forces around the turbine are discussed in the safety point of view, which need to be investigated to prevent from bending and collapse of the turbine main shaft.
  • KURODA Ichiro, SAKAKIBARA Akihiko, SASAKI Toshio, MURAI Yuichi, NAGAI Niro, YAMAMOTO Fujio  Japanese journal of multiphase flow  22-  (2)  161  -174  2008/06/15
  • OISHI Yoshihiko, BREND Mark, THOMAS Peter J., MURAI Yuichi, TAKEDA Yasushi  日本流体力学会年会講演論文集  2008-  178  -178  2008  
    Vortex rings translating along the central axis of rigidly rotating fluid are measured by particle tracking velocimetry. The vortex rings with the background rotation break up earlier than these without the rotation. The reason is explained by the momentum exchange promoted between the vortex ring and the surrounding fluid. From the data analysis for translational velocity, vorticity, circulation, and momentum of the vortex ring, we discuss how the spatial development of vortex ring is affected by the rotation.
  • TAKAHASHI Junpei, YANO Kanako, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, YANAGISAWA Takatoshi, YAMAGISHI Yasuko  日本流体力学会年会講演論文集  2008-  61  -61  2008  
    Transition mechanisms of convection cell induced by internal heat sources in a shallow fluid layer are investigated experimentally. We attempt to determine the flow structure in a cell by Particle Image Velocimetry (PIV). Simultaneous multi-layer measurement is performed by color-striped light sheet and transitional state of convection cell is investigated. Vertical velocity component is also obtained and we investigate how cell behaves with respect of R_1 quantitatively. We confirmed cell transition is strongly related with development of descending flow at the center of a cell. Cell dilatation process is described as a consequence descending flow develops and strongly expands at the bottom of the fluid layer.
  • 太田 翔子, 田坂 裕司, 村井 祐一, 武田 靖, 日夏 宗彦, 児玉 良明  海上技術安全研究所報告  8-  (2)  224  -224  2008
  • YOSHIDA Koji, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  Fluids engineering conference ...  2007-  "102  -1"-"102-4"  2007/11/17  
    Relationship between drag reduction and microbubble motion in a vertical Taylor-Couette flow is investigated by visualization of r-z cross section. We have measured the vorticity distribution in two-phase condition by means of particle tracking velocimetry (PTV). The bubble distribution shows two modes as Re number changes, i.e. toroidal and spiral modes. In low Re number region, the vortex structure is modified significantly by the bubbles. The presence of bubbles provides elongation of vortical wavelength to be around 1.5 times as that without bubbles. This alternation of the cell yields a large reduction ratio of the shear stress in low Re number region while the drag reduction effect is weakened as Re number increases for the high kinetic energy of the cell motion.
  • OHTA Shoko, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, HINATU Munehiko, KODAMA Yoshiaki  Fluids engineering conference ...  2007-  "911  -1"-"911-4"  2007/11/17  
    Friction drag accounts for 80 % of the total drag for large ships, and hence microbubble drag reduction is expected as one of the most feasible ways to reduce it because of less environmental impact and easy installation. The basic experiment to confirm the drag reduction effect was performed from 1970's, and it comes to the stage of a practical examination for moving ships. As a method to assess the bubble-originated alternation of the boundary layer structure beneath a moving ship, we have designed a ship-mounting type of ultrasound probe to apply ultrasound velocity profiler (UVP) and examined the measurement performance for a long towing-ship in NMRI 400m-run facility. The probe emits 2MHz-pulsed ultrasound at 75 degree to the main flow direction to acquire the turbulent velocity profile up to 7.2m/s in the fastest case. This report mainly describes the measurement method of bubble distribution in the boundary layer. The method is constructed by the probability theory of ultrasound reflection on individual bubbles, and examined by numerical simulation. This application to a 50m-model ship reveals that the water flow boundary layer changes to steep profile where the bubbles are concentrated.
  • Murai Yuichi  Fluids engineering conference ...  2007-  "WS1  -4-1"-"WS1-4-4"  2007/11/17  
    A variety of frictional drag reductions achieved by from microbubbles to large film-like bubbles are presented. The most curious fact found from their experiments is that the friction is so sensitively reduced by bubbles when the bubbles are smaller than the fundamental eddies in turbulence. This situation was, in the past, understood to be explained by homogenous model such as by Rheological expression because of less relative velocities between two phases. However the measurement results are unmatched with such a simplified theory. The discussion for the fluid dynamics mechanism is now advancing to extremely complicated model because of inevitable non-homogenous two-phase high-sheared turbulence. Despite to the knowledge accumulated to date, the key process hidden in the drag reduction still must be extracted to utilize the phenomenon as engineering technology that has already begun in maritime innovation. This report mentions how much the original bubbles have such potential to alter the boundary layer as well as the key phenomenon that triggers the effective drag reduction.
  • TAKEUCHI Hirotaka, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  Fluids engineering conference ...  2007-  "308  -1"-"308-4"  2007/11/17  
    Particle image velocimetry (PIV) is applied to measurement of airflows around permeable circular cylinders. The aim of this study is to understand the wake structure of a permeable object subjected to uniform flow, such as buildings under construction, steel tower frames, and natural trees. The experimental model of the permeable cylinder is made of squared meshed sheet with a mesh number 32 and an opening ratio of 0.54. The following points are newly found when the flow field is compared to that of a solid cylinder. 1: In case of the permeable cylinder, the turbulence peak appears in a downstream region relative to the solid cylinder, because generation of vortex street is delayed significantly. 2: The drag is not simply estimated only by the opening ratio of the permeable cylinder. 3: The permeable cylinder has non-periodical vortex shedding. This has been confirmed from the correlation coefficient between the enstrophy and the turbulence intensity, which is greater than the solid one.
  • YANO Kanako, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi, Patrice Le Gal  北海道支部講演会講演概要集  2007-  (46)  83  -84  2007/09/29
  • TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2007-  (46)  81  -82  2007/09/29
  • TAKAHASHI Junpei, YANO Kanako, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2007-  (46)  85  -86  2007/09/29
  • FUJIKAWA Shigeo, MURAI Yuichi  Japanese journal of multiphase flow  21-  (3)  297  -300  2007/09/15
  • TASAKA Yuji, YANO Kanako, MURAI Yuichi, TAKEDA Yasushi, YANAGISAWA Takatoshi  日本流体力学会年会講演論文集  2007-  168  -168  2007  
    This study aims to clarify the mechanism of an oscillating motion of the convection cell appearing in the thermal convection of a liquid gallium layer. Ultrasonic Velocity Profiling (UVP) was employed to visualize and quantitativelly estimate the fluid motion of the convection. Obtained spatio-temporal velcocity distributions well represent the convective motion including the oscillating motion of the cell. A result of a numerical simulation, which was done in the same condition with the experiment, and experimental estimation of the Reynolds number mension that the oscillating motion may be induced by instability of separated thermal boundary layers. Thermal convection in uniform magnetic field was also investigated by means of UVP. The obtained spatio-temporal velocity distribution showed us a two dimensionalization of the convective motion as influence of the applying magnetic field.
  • NOMURA Yuuta, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  日本流体力学会年会講演論文集  2007-  164  -164  2007  
    We investigated azimuthal behaviors of Taylor-Couette flow on the azimuthal cross section by flow visualization using Kalliroscope flakes, and by image analysis of the obtained movie. Kalliroscope flakes are platelet and can make shear flow visible. Wavy vortex flow mode (WVF) in which an azimuthal wave mode superposes Taylor vortex flow mode (TVF) was investigated. Wave number and phase velocity of the azimuthal wave appearing in WVF at higher Reynolds number were determined by image analysis. Azimuthal flow structure of modulated wavy vortex flow mode (MWVF) was clearly visualized and the modulation component of MWVF was investigated by Fourier analysis of a temporal variation of brightness distribution extracted from a movie of visualized flow. Continuous wavelet analysis indicates that the modulation might occur for all wave regions but with different characteristics.
  • Kodama Yoshiaki, Sugiyama Kazuyasu, Murai Yuichi, Kawamura Takafumi  海上技術安全研究所報告  7-  (3)  257  -304  2007  
    In order to clarify the skin friction reduction mechanism by microbubbles, both experiment and numerical simulation of turbulent channel flow with bubbles were carried out in the same parameter range, and were compared. In the experiment, silicone oil ten times more viscous than water has been used, in order to lower the Reynolds number to that of numerical simulation. The surface tension of the Silicone oil is 1/3 of that of water. In the numerical simulation, two numerical methods have been used. One is the Force Coupling Method (FCM), in which bubbles are assumed to be rigid and the influence of bubbles to the flow is simulated by body forces. The other is the Front-Tracking Method (FTM), in which fluid phase and gas phase are solved simultaneously and bubble shape is allowed to deform by being expressed with polynomials. In the experiment the Reynolds number (Re) is 2,777 to 4,500, and the Weber number (We) is 200. The experimental values of local skin friction shows that the flow is semi-laminar at Re=2,777 in the non-bubble condition, and that, by injecting bubbles, the skin friction increases to the turbulent flow value, which means that bubble injection stimulates the flow and turns it to fully turbulent. At Re=3,734(3,811) the flow is already fully turbulent in the non-bubble condition, and therefore adding bubbles has little influence on the flow, resulting in little change in the skin friction. At even higher Reynolds number of nearly 4,500, adding bubbles decreases skin friction slightly. The Reynolds number of the numerical simulation using FTM is 3,000. The time history of skin friction shows that at the wall where bubbles are clustered by buoyancy local skin friction tends to show slight decrease by adding deformable bubbles (We=100). However, by adding less deformable bubbles (We=50) local skin friction slightly increases. Computation at We=200 has blown up. The local skin friction in the FCM computation at Re=4,000 shows 2.3% increase by adding (rigid) bubbles. Therefore it may be stated that, at Re=3,000, addition of deformable bubbles tends to decrease skin friction, while addition of less deformable bubbles, or rigid bubbles, tends to increase skin friction. In order to carry out numerical simulation of turbulent shear flow with bubbles at higher Reynolds number, the simulation of the homogeneous turbulent shear flow (HTSF) with deformable bubbles has been carried out. The result shows that large turbulent Reynolds number, smaller shear Reynolds number and large Weber number have positive influence on the microbubble drag reduction. The increase of the turbulent Reynolds number of HTFS corresponds to the increase of the Reynolds number of the turbulent channel flow (TCF), and therefore the result agrees with the experimental result that added bubbles decrease skin friction at higher Reynolds number but not at lower Reynolds number. The Weber number dependence of the HTSF result can be compared directly with that of TCF, Thus the result confirms that bubble deformation acts to decrease skin friction.
  • MURAI Yuichi  JSME北海道支部第46回講演会概要集, 2007  79  -80  2007
  • Kondoh Takayuki, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Procee[d]ings of Thermal Engineering Conference  2006-  251  -252  2006/11/23  
    Thermal efficiency of polymer electrolyte fuel cell extremely depends on a water distribution in Gas Diffusion Layer (GDL). Fuel cell model was prepared in order to investigate the water distribution in GDL by ultrasonic techniques. Acoustic impedance of GDL, which is porous plate of carbon, was estimated as bulk model to know approximated value of reflection ratio of ultrasonic echo. We attempted to measure an instantaneous ultrasonic echo that changes by the quantity of the water to detect existing water in GDL. And we focused on the phase delay and the amplitude change of the ultrasonic echo and analyzed the waveform.
  • Murai Yuichi, Tasaka Yuji, Ohta Shoko, Takeda Yasushi  Procee[d]ings of Thermal Engineering Conference  2006-  249  -250  2006/11/23  
    Ultrasonic velocity profiler (UVP) is applied to measurement of water flow under the bottom surface of a ship. The aim of this study is to establish the practical utilization of UVP system for large ships whose power loss is generally dominated by frictional drag. As the first phase, the measurement performance is evaluated for capturing the turbulent boundary layer of a small model ship using a new ultrasonic transducer. The experiments are performed for a towing ship in a shallow pond and also for a freely supported ship in an open channel. A wedge type of ultrasonic transducer is designed so that the flow is undisturbed with it. The velocity profile including the boundary layer is successfully obtained after suitable post-processing is implemented to remove erroneous data caused by multiple reflections. Data analysis is also made to estimate the skin friction from the profiles measured.
  • Kon Seiji, Yamaguchi Kouhei, Obayashi Hironari, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2006-  "1708  -1"-"1708-4"  2006/10/28  
    Unit of Vector-UVP system, which is an advanced UVP system to measure three directional velocity components on a line by using multiple transducers, was developed. To optimize the Vector-UVP system, we attempted to determine an acoustic field generated by a focusing transducer, which can focuses ultrasound via acoustic lens mounted at the head of the transducer. The acoustic intensity was measured using a small hydrophone by scanning the sound field. It is also theoretically calculated by solving two-dimensional wave equation to validate the measured results, such as focal point of the ultrasonic beam. We also estimated the influence of an intermediate wall existing between target fluid and the transducer on the acoustic field. With the estimated results, the measurement volume and the measurement area were determined so that the system is optimized. The system was applied to the measurement of two directional velocity components of Karmann vortices in a wake of a circular cylinder to demonstrate the applicability to multi-dimensional unsteady flow. From the measured velocity vector profile, the two-dimensional vorticity distribution were validly detected using the present vector-UVP system after Taylor's frozen hypothesis was considered.
  • KOJIMA Shinya, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  Fluids engineering conference ...  2006-  "1705  -1"-"1705-4"  2006/10/28  
    The discharge of the overflow at a dam is currently determined by applying an empirical equation estimated on ideal system to water level at the dam. However the real overflow on large scale has many uncertain factors and thus the estimated discharge has large errors, which may be order of several ten percent. Until now, we have studied an overflow measurement by using ultrasonic velocity profiler (UVP) to realize more accurate measurement of the discharge (Kashiwaguma, 2003). Cross-sectional velocity distribution over the weir setting in an open channel was measured by UVP and discharge calculated from velocity distribution was compared with discharge determined from the empirical equation. That system has slightly error because of rough detecting the position of free surface on measurement line. To reduce error in the measurement of the discharge, we must acquire the position exactly. In this study, we attempted to utilize the amplitude information of US echo which has not been used to calculate the velocity profile in conventional UVP. The velocity profile was measured in the vertical direction on the condition accompanying free surface in an open channel. The time evolution of the free surface displacement was measured by using the amplitude information of reflected ultrasound at the surface. The measured position was compared with an alternative measurement method based on the position meter fixed on the measurement line of UVP and then the accuracy of the present method was verified.
  • Murai Yuichi, Oishi Yoshihiko, Takeda Yasushi, Thomas Peter J.  Fluids engineering conference ...  2006-  "1702  -1"-"1702-4"  2006/10/28  
    Vortex ring migrating with background rotation is analyzed experimentally. The rotation field is given by rigid rotation whose axis is parallel to the migrating direction. The transverse velocity and the internal flow structure of the vortex ring are measured by ultrasonic velocity profiler (UVP) with changing the stroke and the velocity of piston-type vortex ring generator. The results show that the transverse velocity decreases with the rotation but keeps its original value when the stroke is long. This trend is explained by the time scale of fluid circulation inside the vortex ring.
  • KOJIMA Shinya, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  Fluids engineering conference ...  2006-  "1705  -a"  2006/10/28
  • Kon Seiji, Yamaguchi Kouhei, Obayashi Hironari, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2006-  "1708  -a"  2006/10/28
  • Murai Yuichi, Oishi Yoshihiko, Takeda Yasushi, Thomas Peter J.  Fluids engineering conference ...  2006-  "1702  -a"  2006/10/28
  • Ohashi Junichi, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2006-  "1711  -1"-"1711-4"  2006/10/28  
    As a basic study for developing a two-phase flowmeter by means of ultrasonic velocity profiler(UVP), theoretical and numerical estimations of the phase distribution measurement are performed. The measurement accuracy depends on the number of ultrasonic measurement lines. When the azimuthal resolution is lacked, the error grows up for low void fraction conditions. Considering the relative resolution to radial direction, the sufficient number of the lines is concluded as 8. A practical measurement for a slug flow is also carried out to understand the internal secondary flow that affects on the flow rate measured by UVP.
  • OISHI Yoshihiko, MURAI Yuichi, LATRACHE Noureddine, TASAKA Yuji, TAKEDA Yasushi  Fluids engineering conference ...  2006-  "708  -1"-"708-4"  2006/10/28  
    Flow visualization of the turbulent structure in a bubbly channel flow is performed at Re=1333. Kalliroscope is used as the tracer, which is a dispersion of flake-like micros-scale particles with high optical reflection. The optical characteristic of the particle is analyzed by numerical simulation to confirm that the more the reflection intensity increases, the more the shear increases. The results of the application to actual visualization reveal the structures of the streamwise vortices and the low-speed streaks. When the micro bubbles are injected in the channel, the turbulent structure changes to a macular state, i.e. the original longitudinal structure is shortened by the bubbles.
  • TASAKA Yuji, KOJIMA Shinya, YOKOYAMA Kaoru, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2006-  (45)  179  -180  2006/09/25
  • TAKEUCHI Hirotaka, TASAKA Yuji, OISHI Yoshihiko, MURAI Yuichi, TAKEDA Yasushi, TEZUKA Hideaki, MORI Michitsugu  北海道支部講演会講演概要集  2006-  (45)  43  -44  2006/09/25
  • MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  北海道支部講演会講演概要集  2006-  (45)  69  -70  2006/09/25
  • OHTA Shoko, KONDOH Takayuki, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2006-  (45)  67  -68  2006/09/25
  • MURAI Yuchi, FUJII Hideki, MATSUBARA Yoshiaki, OISHI Yoshihiko, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl.  26-  (1)  315  -316  2006/07/01
  • OISHI Yoshihiko, MORINAGA Masato, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi, THOMAS Peter J.  可視化情報学会誌. Suppl.  26-  (1)  333  -334  2006/07/01
  • HARA Kazuyuki, SAKAKIBARA Akihiko, MURAI Yuichi, YAMAMOTO Fujio  可視化情報学会誌. Suppl.  26-  (1)  313  -314  2006/07/01
  • TASAKA Yuji, YANAGISAWA Takatoshi, MURAI Yuichi, TAKEDA Yasushi  可視化情報学会誌. Suppl.  26-  (1)  353  -354  2006/07/01
  • SAKAKIBARA Akihiko, KURODA Ichiro, SASAKI Toshio, NAGAI Niro, MURAI Yuichi, YAMAMOTO Fujio  可視化情報学会誌. Suppl.  26-  (1)  311  -312  2006/07/01
  • MORINAGA Masato, OISHI Yoshihiko, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl.  26-  (1)  289  -290  2006/07/01
  • TASAKA Yuji, YOSHIDA Masataka, MURAI Yuichi, TAKEDA Yasushi, YANAGISAWA Takatoshi  日本流体力学会年会講演論文集  2006-  177  -177  2006  
    Thermal convection in liquid gallium layer is investigated as a fundamental study for Rayleigh-Benard convection in low Prandtl number fluid using ultrasonic velocity profiler, UVP. Measured velocity profiles visualize a convective motion in the liquid gallium layer, and it is a roll shape motion. Spatio-temporal velocity profile shows that there are two types of spatial fluctuation of the convection roll. Two axes-simultaneous velocity profile measurement clarifies that expand and contraction of convection roll has a phase delay on the direction of the rotating axis of the roll. Frequency analysis of the obtained instantaneous velocity distribution shows that the convective motion has unique frequency component of the velocity fluctuation at the boundaries between the rolls. The frequency component cannot be detected at smaller Rayleigh number, under R=1×10^4. The frequency is proportional to the Rayeigh number to the power 0.376.
  • Morinaga Masato, Tasaka Yuji, Takeda Yasushi, Murai Yuichi  日本流体力学会年会講演論文集  2006-  128  -128  2006  
    We attempted a direct energy injection to a higher flow mode of Taylor-Couette flow by using modulated rotation of an inner cylinder. Wavy vortex flow (WVF) mode was chosen as target of the energy injection and then a characteristic frequency of WVF is set to a basic frequency of the modulated rotation. Ultrasonic velocity profiler (UVP) measured an instantaneous velocity profile of the flow under the modulated rotation, and influence of the modulation in the flow was investigated. The measurement of instantaneous velocity profile of axial and radial component of flow velocity showed that this method cannot increase energy of WVF mode but can change shape of spectrum sharp at frequency of wavy motion in WVF.
  • NOMURA Yuuta, MORINAGA Masato, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  日本流体力学会年会講演論文集  2006-  127  -127  2006  
    We attempted to investigate flow structures of Taylor-Couette Flow (TCF) at the azimuthal cross section by flow visualization using Kalliroscope flakes, which is platelet and can make share flow visible, and by image processing of the obtained image. It is confirmed that the established measurement technique can reproduce structure of the Taylor vortex. This technique is also applied to determine wavenumber and phase velocity of the azimuthal wave appearing in wavy vortex flow (WVF) mode at higher Reynolds number. Moreover, azimuthal flow structure of modulated wavy vortex flow (MWV) is clearly visualized and modulation component of MWV is detected by the image processing, which is Fourier analysis of temporal variation of brightness profile extracted from a movie of visualized flow.
  • Murai Yuichi, Tasaka Yuji, Takeda Yasushi  Fluids engineering conference ...  2005-  155  -155  2005/10/28
  • Yamaguchi Kohei, Kon Seiji, Ohbayashi Hironari, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2005-  161  -161  2005/10/28
  • Fukuda Hiroshi, Oishi Yoshihiko, Murai Yuichi, Kodama Yoshiaki, Yamamoto Fujio  Fluids engineering conference ...  2005-  149  -149  2005/10/28
  • OISHI Yoshihiko, FUKUDA Hiroshi, MURAI Yuichi, KODAMA Yoshiaki, TAKEDA Yasushi, YAMAMOTO Fujio  Fluids engineering conference ...  2005-  67  -67  2005/10/28
  • Oiwa Hiroshi, Murai Yuichi, Yamamoto Fujio  Fluids engineering conference ...  2005-  150  -150  2005/10/28
  • Sakakibarta Akihiko, Kuroda Ichiro, Sasaki Toshio, Nagai Niro, Murai Yuichi, Yamamoto Fujio  Fluids engineering conference ...  2005-  151  -151  2005/10/28
  • Ashihara Masaaki, Kitagawa Atsuhide, Murai Yuichi, Yamamoto Fujio  Fluids engineering conference ...  2005-  72  -72  2005/10/28
  • Inaba Kazumasa, Ohashi Jyunichi, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2005-  65  -65  2005/10/28
  • 藤井 秀基, 大石 義彦, 田坂 裕司, 村井 祐一, 武田 靖  北海道支部講演会講演概要集  2005-  (44)  62  -63  2005/10/08
  • MURAI Yuichi, KUDO Kiyoshi, MIYAGI Naoki  形の科学会誌 = Bulletin of the Society for Science on Form  20-  (1)  77  -78  2005/06/01
  • 北川 石英, 杉山 和靖, 笹木 俊男, 村井 祐一  日本機械学會誌  108-  (1038)  348  -348  2005/05/05
  • MURAI Yuichi, FUJII Hideki, NISHIMOTO Masahiro, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl.  25-  (1)  31  -32  2005/03/15
  • Murai Yuichi, Nakada Taishi, Yamamoto Fujio  Fluids engineering conference ...  133  -133  2005
  • Oiwa Hiroshi, Murai Yuichi, Yamamoto Fujio  Fluids engineering conference ...  2004-  188  -188  2004/11/24
  • Murai Yuichi, Miyagi Naoki, Miyazaki Koji, Yamamoto Fujio  Fluids engineering conference ...  2004-  77  -77  2004/11/24
  • OHTA Junichi, MONTANI Mitsuto, KUROSE Naoki, MURAI Yuichi, YAMAMOTO Fujio  Transactions of the Japan Society of Mechanical Engineers. Series B.  70-  (693)  1201  -1207  2004/05/25  
    Efficient techniques for cleaning scale in a U-tube of a heat exchanger are desired. Blast cleaning test was carried out using a real size U-tube of 13.5mm in diameter, 8m of straight tube length, and 0.3m in radius of curvature. A combination of plastic particles and glass beads was selected for the blasting media. Swirl motion was added to the blasting media flow. The plastic particle-air two-phase flow with swirl motion in the tube was visualized. The loading ranged from 3.7 to 5.3. The estimated Stokes number was 1700 for the plastic-air two-phase flow. It was observed that just downstream of the bend, flow particle clusters repeatedly followed each other alternatingly located on the upper and lower sides of the tube. In the repeated blast cleaning experiments, it was found that the same characteristic large-scale cleaning distribution occured along the tube.
  • OISHI Yoshihiko, ASHIHARA Masaaki, MURAI Yuichi, YAMAMOTO Fujio  講演論文集  2004-  (41)  53  -54  2004/03/01
  • CHENG Wen, MURAI Yuichi, ISHIKAWA Masa-aki, YAMAMOTO Fujio  可視化情報学会論文集合本 = Transactions of the Visualization Society of Japan  23-  (11)  107  -114  2004/01/31
  • Nakada Taishi, Sasaki Toshio, Murai Yuichi, Yamamoto Fujio  Fluids engineering conference ...  43  -43  2004
  • MURAI Yuichi, NAGAO Jotaro, TAKEDA Yasushi  日本流体力学会年会講演論文集  2004-  206  -207  2004  
    Frictional drag reduction in a horizontal turbulent boundary layer using small bubbles is discussed mathematically and experimentally. Three kinds of turbulent shear stresses are derived from the momentum conservation equation of bubbly flow, i.e., Reynolds shear stress, vertical correlation stress, and triple correlation stress. The experimental data indicate that the triple correlation term among them has an important role to reduce the total frictional drag while Reynolds stress profile has its peak at a far distance from the wall in the case of mixing bubbles. Also, the mean relative velocity between bubbles and liquid in the turbulent boundary layer is derived to estimate the experimental data.
  • SHIMIZU Manabu, OIWA Hiroshi, MURAI Yuichi, YAMAMOTO Fujio  The Computational Mechanics Conference  2003-  (16)  109  -110  2003/11/22  
    The effective viscosity of bubbly liquid is governed not only by void fraction but also by bubble's deformation whose effect is expressed with Capillary number. In this study, two kinds of bubbly two-phase flow are analyzed with using the model of the effective viscosity to confirm the effect of bubble's deformation on the time-averaged velocity profiles in laminar flow conditions.
  • Murai Yuichi, Oiwa Hiroshi, Yamamoto Fujio  Fluids engineering conference ...  2003-  187  -187  2003/09/18
  • OISHI Yoshihiko, MURAI Yuichi, ISHIKAWA Masaaki, YAMAMOTO Fujio  Fluids engineering conference ...  2003-  156  -156  2003/09/18
  • Nakajima Yoichi, Murai Yuichi, Ido Takehiro, yamamoto Fujio  Fluids engineering conference ...  2003-  86  -86  2003/09/18
  • ASHIHARA Masaaki, KITAGAWA Atsuhide, MURAI Yuichi, YAMAMOTO Fujio  Fluids engineering conference ...  2003-  20  -20  2003/09/18
  • SASAKI TOSHIO, MURAI Yuichi, YAMAMOTO Fujio  Japanese journal of multiphase flow  17-  (3)  296  -304  2003/09/15
  • UENO Yasutaka, MURAI Yuichi, YAMAMOTO Fujio  可視化情報学会誌. Suppl.  23-  (1)  57  -58  2003/07/01
  • ISHIKAWA Masa-aki, MURAI Yuichi, SAKAI Kosuke, TODA Shin-ichi, YOSHIKAWA Shinji, YAMAMOTO Fujio  Journal of the Visualization Society of Japan  23-  (1)  373  -376  2003/07/01
  • NAKAJIMA Yoichi, IDO Takehiro, ISHIKAWA Masaaki, MURAI Yuichi, YAMAMOTO Fujio  講演論文集  2003-  (40)  85  -86  2003/03/01
  • SASAKI Toshio, NAGAI Niro, MURAI Yuichi, YAMAMOTO Fujio  講演論文集  2003-  (40)  91  -92  2003/03/01
  • ISHIKAWA Masaaki, MURAI Yuichi, SAKAI Kosuke, YAMAMOTO Fujio, TODA Shinichi, TAMAYAMA Kiyoshi  Proceedings of the ... International Conference on Nuclear Engineering. Book of abstracts : ICONE  2003-  283  -283  2003
  • 北川 石英, 芦原 将彰, 村井 祐一, 山本 富士夫  海上技術安全研究所報告  3-  (2)  224  -224  2003
  • OIWA Hiroshi, MURAI Yuichi, TAKAHASHI Yoshiaki, YAMAMOTO Fujio  Japanese journal of multiphase flow  16-  (4)  372  -379  2002/12/15
  • ISHIKAWA Masa-aki, MURAI Yuichi, RYONO Yoshiaki, SAKAI Kosuke, TODA Shin-ichi, TAMAYAMA Kiyoshi, YAMAMOTO Fujio  Journal of the Visualization Society of Japan  22-  289  -292  2002/07/01
  • IDO Takehiro, SHIMOOKA Hisaharu, SHIMIZU Hiromasa, ISHIKAWA Masa-aki, MURAI Yuichi, YAMAMOTO Fujio, MASUDA Yoriyasu  Journal of the Visualization Society of Japan  22-  385  -388  2002/07/01
  • MURAI Yuichi  Japanese journal of multiphase flow  16-  (1)  44  -47  2002/03/15
  • MATSUBARA Tomoaki, ISHIKAWA Masaaki, MURAI Yuichi, YAMAMOTO Fujio  講演論文集  2002-  (39)  99  -100  2002/03/08  
    Combined technique of Particle Imaging Velocimetry (PIV) in conjunction with Computational Fluid Dynamics (CFD) makes it possible to predict detailed fluid flow structures. Turbulent flow containing fine solid particles in a channel is one of typical examples which are not solved only by PIV nor by CFD. In this study, the solid particle behavior in a converging channel is predicted by theoretical equations after the carrier phase flow field is measured by PIV. The results have shown the dependency of the particle behavior on its force components, such as inertia and lift forces.
  • OHTA Junichi, SUGIMOTO Taketoshi, MURAI Yuichi, SEKI Masahiko, KURODA Yuji, YAMAMOTO Fujio  Fluids engineering conference ...  2001-  105  -105  2001/09/28
  • ASHIKAGA Masatoshi, OGINO Yurika, TAKAHASHI Asami, MINATO Shigeharu, ANDO Koichi, KUDO Kiyoshi, SHIMIZU Hiromasa, MATSUBARA Tomoaki, MURAI Yuichi  可視化情報学会誌 = Journal of the Visualization Society of Japan  21-  71  -72  2001/09/01
  • SHIMIZU Hiromasa, IDO Takehiro, MURAI Yuichi, YAMAMOTO Fujio  Journal of the Visualization Society of Japan  21-  51  -54  2001/09/01
  • ISHIKAWA Masa-aki, IDO Takehiro, KITAGAWA Atsuhide, MATSUBARA Tomoaki, MURAI Yuichi, YAMAMOTO Fujio  Journal of the Visualization Society of Japan  21-  129  -132  2001/07/01
  • FUJIMOTO Koichi, MURAI Yuichi, MINAMI Tomokazu, YAMAMOTO Fujio  Transactions of the Japan Society of Mechanical Engineers. Series B.  67-  (658)  1400  -1407  2001/06/25  
    This paper concerns with flow visualization and image measurement of bubbly flows around several shapes of obstacle. Coaxially confined twin rectangular tanks are constructed in order to provide a wide two-dimensional uniform bubble distribution upstearm of the obstacle. The experiments show that a quite large two-phase convection is induced by inserting the obstacle into the bubbly flow. Spatial scale of the two-phase convection depends on the shape of the obstacle as well as its arrangement. Measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by PIV and PTV, explores the detailed mechanism of generating the convection. Especially, the interaction between accumulated bubbles in upstream the object and downward liquid flow behind the object determines the scale of the two-phase convection.
  • OHIWA Hiroshi, MURAI Yuichi, YAMAMOTO Fujio  計算工学講演会論文集  6-  (1)  261  -264  2001/05/30
  • MURAI Yuichi, OHNO Yasushi, HASSAN Abdulmouti, YAMAMOTO Fujio  Transactions of the Japan Society of Mechanical Engineers. Series B.  67-  (657)  1120  -1127  2001/05/25  
    Flow in the vicinity of free surface induced by a bubble plume is utilized as one of effective ways to control the surface floating substances on lakes, oceans, as well as in various kinds of reactors handling a free surface. In this work, a two-dimensional flow analysis based on Eulerian-Lagrangian model and particle tracking velocimetry measurement have been carried out in order to elucidate the surface flow generation process in detail. The present results explore the following points : 1) Surface velocity profile can be predicted by the Eulerian-Lagrangian model with a good agreement with experimental results, 2) maximum velocity of the surface flow increases as large void fraction with small bubble size is supplied, 3) The surface flow is effectively generated in case of bubble plume compared to liquid jet flow because distortion point appears in the vicinity of surface.
  • YAMAMOTO Fujio, MURAI Yuichi  Journal of the Visualization Society of Japan  21-  (80)  2  -7  2001/01/01
  • FUJIMOTO K., ISHIKAWA M., MINAMI T., MURAI Y., YAMAMOTO F.  Journal of visualization  4-  (3)  213  -213  2001
  • IDO Takehiro, MURAI Yuichi, YAMAMOTO Fujio  Transactions of the Japan Society of Mechanical Engineers. Series B.  66-  (649)  2257  -2264  2000/09/25  
    Accurate post-processing methods are required in order to analyze the detailed flow structures from the data of particle tracking velocimetry. In particular, both spatial distributions of vorticity and stream functions cannot be obtained reasonably in the case of sparse data resulting from popular conventional methods. This paper proposes a new post-processing algorithm based on ellipsoidal differential equations which enable to utilize boundary condition data efficiently. The performance of the algorithm is examined by applying them to two-dimensional vortex flows and isotropic turbulent flows. The results reveal that the present algorithm has the highest accuracy in comparison with several popular methods for detecting vorticity, energy, and the energy spectrum.
  • OHIWA Hiroshi, ONO Yasushi, MURAI Yuichi, YAMAMOTO Fujio  Fluids engineering conference ...  2000-  134  -134  2000/09/08
  • 井戸 健敬, 村井 祐一, 山本 富士夫  可視化情報学会誌  20-  (1)  241  -244  2000/07
  • MURAI Yuichi, KITAGAWA Atsuhide  混相流 = Japanese journal of multiphase flow  14-  (1)  115  -116  2000/03/15
  • IDO Takehiro, MURAI Yuichi, YAMAMOTO Fujio  日本機械学会関東支部総会講演会講演論文集  2000-  (6)  181  -182  2000/03/10  
    The Visualization Society of Japan provides PIV-standard images for evaluating PIV and PTV algorithms. By using the PIV-standard images, post-processing methods of PTV have been evaluated by reconstructing the vorticity with or without errors in PTV data. As a result, one of the post-processing methods, named "Biquadratic-ellipsoidal Equation Rearrangement" method, has a good performance in case of no error, but the method is liable to be influenced by the errors.
  • KUDAMATSU Jun, MURAI Yuichi, GANG Chen, YAMAMOTO Fujio  講演論文集  2000-  (37)  213  -214  2000/03/01
  • OHIWA Hiroshi, ONO Yasushi, MURAI Yuichi, YAMAMOTO Fujio  講演論文集  2000-  (37)  215  -216  2000/03/01
  • ASHIHARA Masa-aki, MURAI Yuichi, BAE Dae Seok, YAMAMOTO Fujio  Proceedings of the ... JSME-KSME Thermal Engineering Conference  1-  "1  -319"-"1-324"  2000  
    Bubble motion near a vertical flat wall in a quiescent liquid has been investigated by using particle tracking velocimetry (PTV). The bubbles showed a variety of behavior, such as sliding, flapping, and jumping on the wall. The present study was focused on the sliding behavior to clarify the transition mechanism of bubble's arrangement pattern from homogeneous arrangement to heterogeneous arrangement in the case of high void fraction. From the statistical values of the experimental results, bubble-bubble interaction structure in wall-sliding bubbles was made clear.
  • ISHIKAWA Masaaki, Ido Takehiro, MURAI Yuichi, YAMAMOTO Fujio  日本流体力学会年会講演論文集  2000-  253  -254  2000  
    We have proposed a rearrangement maethod based on Laplace cquation for velocity. It is difficult to obtain first order differential values correctly such as the velocity gradient tensor, because the equation deals with the multi-dimensional linear transformation. There ore, we furthermore adapted Laplace equations for velocity gradient tensor, it was posible to correctly calculate velocities and velocity gradient tensors. This rearrangement method is applied to homogeneous turblent flow, the performance of this method is examined in comparison with the inverse distance rearrangement method.
  • SHINODA Keiji, OHTA Junichi, MURAI Yuichi, YAMAMOTO Fujio  インテリジェント・システム・シンポジウム講演論文集 = FAN Symposium : fuzzy, artificial intelligence, neural networks and computational intelligence  9-  546  -549  1999/10
  • ISHIKAWA Masa-aki, MURAI Yuichi, OHTA Junichi, YAMAMOTO Fujio  年会一般講演  18-  63  -64  1999/07/29
  • MURAI Yuichi, SONG Xiang-Qun, TAKAGI Takashi, ISHIKAWA Masa-aki, YAMAMOTO Fujio, OHTA Junichi  Transactions of the Japan Society of Mechanical Engineers. Series B.  65-  (632)  1339  -1346  1999/04/25  
    The inverse energy cascade, which is one of the important phenomen α to enhance the large scale flow instability in bubbly flow, is investigated by measuring a local two phase flow structure driven by buoyant bubbles using Particle Imaging Velocimetry (PIV). In the PIV, flow field of liquid phase is measured by separating an original image to respective two phase images using a statistical thresholding method for image parameters of bubble and particle. The present results obtained in case that bubble Reynolds number and average void fraction are less than 30 and 1.5% respectively, confirm the presence of a large energy-decaying with slope index of sharper than -5/3 in log log diagram of energy spectrum at high wavenumber region. Also an important relationship between the energy spectrum and bubble-bubble interval distance is detected.
  • MURAI Yuichi, KITAGAWA Atsuhide, SONG Xiang-Qun, YAMAMOTO Fujio, OHTA Junichi  Transactions of the Japan Society of Mechanical Engineers. Series B.  65-  (632)  1347  -1354  1999/04/25  
    The inverse energy cascade in bubbly flow is investigated by a numerical simulation using the Eulerian-Lagrangian model in which the governing equations are formulated with emphasis on the translational motion of bubbles in non-uniform flow. This paper is concerned with the validation of the numerical model and various parametric dependency on the inverse cascade. The calculated results reveal that, 1) continuous growth of the spatial fluctuation scale in a bubble-induced flow is well predicted by the present numerical model and the results have a good analogy with the experimental results which are introduced in our first report, 2) the strong relationship between energy-decaying process and bubble-bubble distance interval identified also by the present analysis, 3) the slope of energy-decaying at high wavenumber region depends on the kinetic viscosity of liquid, and that at low wave number region depends on inuniformity of buoyancy distribution which changes due to the bubble motion.
  • MURAI Yuichi, WATANABE Masao, HOSOKAWA Shigeo, FUJIKAWA Shigeo  混相流 = Japanese journal of multiphase flow  13-  (1)  61  -62  1999/03/15
  • 太田 淳一, 村井 祐一, 山本 富士夫  福井大学地域共同研究センタ-年報  7-  86  -89  1999
  • MURAI Yuichi, MATSUMOTO Yoichiro, SONG Xiang-Qun, YAMAMOTO Fujio  Transactions of the Japan Society of Mechanical Engineers B  64-  (626)  3257  -3263  1998/10/25  
    Turbulence structure in rising bubbly flow driven by bubble buoyancy was analyzed by using the Eulerian-Lagrangian equation model. A new calculation method for two-way interaction between dispersed bubble and liquid phase was proposed to simulate accurately the local fluctuation of liquid flow induced by bubble migration. The present two-dimensional simulation revealed that, (1) the turbulence structure had the longer wave length in vertical direction in case of the larger bubble, (2) the wave spectrum of kinetic energy of the liquid phase depended sensitively on the average void fraction and the lift force of bubble.
  • MURAI Yuichi, IDO Takehiro, ISHIKAWA Masa-aki, YAMAMOTO Fujio  Transactions of the Japan Society of Mechanical Engineers B  64-  (626)  3249  -3256  1998/10/25  
    Since velocity vectors obtained by Particle Imaging Velocimetry are distributed discretely depending on the number density of tracer particles seeded in the objective flow, a new estimation algorithm to reconstruct the whole-field flow has been proposed using the Laplace equation for velocity vector and the Poisson equation for velocity correction potential. Performance of the algorithm was examined with two-dimensional vortex flow, and the validity was evaluated quantitatively by two-dimensional correlation coefficient. The present algorithm was applied to torque converter internal flow, and the results reveal that the present method is applicable for various conditions to analyze the whole-field flow structure.
  • IDO Takehiro, MURAI Yuichi, YAMAMOTO Fujio  Journal of the Visualization Society of Japan  18-  71  -74  1998/07/01
  • MURAI Yuichi, MATSUMOTO Yoichiro  Transactions of the Japan Society of Mechanical Engineers. Series B.  63-  (611)  2283  -2288  1997/07/25  
    A numerical analysis using the Lagrangian tracking method for bubbly flow was carried out to elucidate the three-dimensional detailed flow structure and the turbulence mechanism of a bubble plume, which has various interaction between gas and liquid phases. The results revealed that the bubble plume exhibits several kinds of three-dimensional structures with spiral and sinuous behaviors, depending on bubble size and void fraction. This macroscopic structure shows good agreement with experimental observation. Also, the bubble plume has a turbulence component, called pseudo turbulence with high frequency which is caused by the migration of large bubbles with large slip velocity inside the bubble plume.
  • MURAI Yuichi, MATSUMOTO Yoichiro  Transactions of the Japan Society of Mechanical Engineers. Series B.  63-  (611)  2277  -2282  1997/07/25  
    Detailed flow structure of bubbly flows observed in a bubble plume is investigated by numerical simulation using the Lagrangian tracking method which can treat the bubble movement with high accuracy. Governing equations are formulated with emphasis on the translational motion of bubble in non uniform unsteady liquid flow. Numerical results reveal the dependency of bubble size distribution on the flow behavior and show good agreements with experimental results. In this 1st report, two-dimensional bubble plumes are chosen for analysis of detailed flow structure in bubbly flow.
  • HASSAN Abdul-Mouti, YAMAMOTO Fujio, MURAI Yuichi, KOBAYASHI Yasuhiro  Journal of the Visualization Society of Japan  17-  239  -242  1997/07/01
  • YAMAMOTO Fujio, WADA Ari-isa, SONG Xiang-Qun, MURAI Yuichi, ISHIKAWA Masa-aki, IGUCHI Manabu  Journal of the Visualization Society of Japan  17-  129  -132  1997/07/01
  • ISHIKAWA Masa-aki, YAMAMOTO Fujio, IGUCHI Manabu, MURAI Yuichi, WADA Ari-isa  Journal of the Visualization Society of Japan  16-  23  -26  1996/11/01
  • MURAI Yuichi, TAKAGI Shu  混相流  10-  (3)  327  -328  1996/09/15
  • MURAI Yuichi, MATSUMOTO Yoichiro  Transactions of the Japan Society of Mechanical Engineers. Series B.  62-  (593)  85  -92  1996/01/25  
    Bubbly flows exhibit various structures, such an incompressible or compressible behavior depending on the void fraction. In the present study, a new numerical method is developed for bubbly flows in order to treat the compressibility stably and effectively, by derivation of the pressure equation from the governing equations based on the two-fluid model. By simulations of several different bubbly flows including a transonic flow, it has been shown that the present method is applicable to wide range bubbly flows in compressibility, and also that calculation efficiency and stability are better than the other solver.
  • MATSUMOTO Yoichiro, MURAI Yuichi  Transactions of the Japan Society of Mechanical Engineers. Series B.  61-  (588)  2818  -2825  1995/08/25  
    A bubble-driven plume in a tank with a free surface is investigated numerically using the bubble flow model equations which are formulated with emphasis on the relative transverse motion and volumetric change of the bubble. A numerical scheme is developed by the derivation of the pressure equation for the bubbly flow in order to treat the effects of the relative motion between two phases and the compressibility of the bubble accurately. From the numerical results, the three-dimensional flow structure of the bubble-driven plume has been shown in detail, where there are turbulences on various scales caused by the interaction of liquid convection and bubble motion.

Books etc

  • 流体計測法
    村井祐一 (Joint editor混相流)
    日本機械学会編，全504頁 (2022) 2022/04
  • Special issue, Nuclear Engineering and Design
    Y.Murai, G.Tryggvason (Joint work)
    2018/08
  • PIV Handbook 2018
    Yuichi MURAI (Joint work)
    2018/06
  • Special Issue for the 9th International Symposium on Measurement Techniques for Multiphase Flows (ISMTMF2015)
    Y.Murai (Editor)
    IoP Measurement Science and Tech. 2016/10
  • 混相流研究の進展（精選論文集）
    村井祐一 (Editor)
    学術出版印刷 2015/10
  • マイクロバブル（ファインバブル）のメカニズム・特性制御と実際応用のポイント
    村井 祐一ほか (Joint work)
    2015/03
  • 微細気泡の最新技術
    村井 祐一ほか (Joint work)
    2014/08
  • Ultrasonic Doppler Velocity Profiler for Fluid Flow
    Y.Murai (Joint work)
    2012/09
  • 工学の基礎 流体力学
    村井 祐一 (Joint work)
    培風館 2009/04
  • マイクロバブルの最前線
    村井祐一ほか (Contributor第1章 マイクロバブルプルーム)
    共立出版 2009/04
  • 実験力学ハンドブック
    村井 祐一ほか (Contributor第29章 衛生工学)
    朝倉書店 2007/04
  • 気液二相流技術ハンドブック
    村井祐一ほか (Contributor第6章 気泡流)
    コロナ社 2006/04
  • 泡のエンジニアリング
    村井 祐一ほか (Contributor第3章、第4章)
    テクノシステム 2005/04
  • 混相流ハンドブック
    村井祐一ほか (Contributor第8章)
    朝倉図書 2004/04
  • 数値流体力学ハンドブック
    村井 祐一ほか (Contributor第8章 混相流解析)
    丸善 2003/04
  • PIV Handbook
    Yuichi MURAI (Contributor第5章 後処理)
    森北出版 2002/04

Presentations

  • Ship frictional drag reduction using hydrofoil bubble generators  [Not invited]
    Y.Murai, I.Kumagai
    11th International Conference on Multiphase Flow (ICMF 2023)  2023/04
  • Color contamination matrix property assessment for improvement of colored smoke PIV  [Not invited]
    Y.Murai, Y.Horimoto, H.J.Park, Y.Tasaka
    14th International Symposium on Particle Image Velocimetry- Chiago, USA  2022/08
  • UVP applied for Doppler scanning of fruit-internal structures and its working principle  [Not invited]
    Y.Murai, T.Yoshida, H.J.Park, Y.Tasaka
    13th International Symposium on Ultrasound Doppler Method 2021 - Zurich  2022/06
  • Frictional drag reduction by controlling of bubble injection  [Invited]
    Y.Murai
    AQUA meeting - Keynote No.1 (2022)  2022/05
  • Current multiphase flow research activities in Japan and the U.S.  [Invited]
    Y.Murai, G.Tryggvason
    U.S.-Japan Seminar on Two-Phase Flow Dynamcs 2022 - Michigan  2022/05
  • Slug-jamming of gas-liquid two-phase flows in a helically coiled tube  [Not invited]
    Y.Murai, M.Ishikawa
    U.S.-Japan Seminar on Two-Phase Flow Dynamcis 2022 - Michigan  2022/05
  • Savonius wind turbine performance in high turbulence and its improvement by jet supply  [Not invited]
    Y.Murai, T.Umemura, R.Sayama, Y.Horimoto, H.J.Park, Y.Tasaka, S.Otomo
    International Conference on Power Engineering 2021 -Kobe  2021/10
  • Keynote: Advances in color particle image velocimetry and color particle tracking velocimetry using color coded volumetric illumination  [Invited]
    Y.Murai
    19th International Symposium on Flow Visualization, Shanghai, China (2021, 9/14-16)  2021/09
  • Keynote: Ultrasonic Doppler measurement of multiphase flows  [Invited]
    Y.Murai
    Int. Multiphase Flow Technology Forum  2020/01
  • Plenary: Velocity profiling rheometry for dispersed multiphase fluids[Plenary Lecture]  [Invited]
    Y.Murai
    10th International Symposium on Measurement Techniques for Multiphase Flow - Hong Kong  2017/12
  • 混相流の流量計測技術  [Invited]
    村井祐一
    産総研 流量計測WG招待講演会  2017/10
  • 改心 科研申請  [Invited]
    村井祐一
    旭川高専 特別講演会  2017/09
  • 気液二相流のスマート制御に基づく船舶の乱流摩擦抵抗低減技術の実用化  [Invited]
    村井祐一, 熊谷一郎, 田坂裕司, 朴 炫珍, 高橋義明
    国立科学博物館出展（日本機械学会賞受賞出展）  2017/07
  • Two-phase flow research activities in Japan, U.S., and E.U.  [Invited]
    Y.Murai, G.Tryggvason, Y.Takeda
    11th Japan-U.S. Seminar on Two-Phase Flow Dynamics  2017/06
  • Laboratory experiments and sea-trials on ship drag reduction by bubble injection[keynote]  [Invited]
    Y.Murai
    9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics (ExHFT-9)  2017/06
  • Advance of particle tracking velocimetry toward ultimate use in multidisciplinary fields  [Invited]
    Y.Murai
    Special Lecture at Swiss Federal Institute of Technology (ETHZ)  2017/03
  • 液状食品の超音波非接触モニタリング技術  [Invited]
    村井祐一, 芳田泰基, 朴炫珍, 田坂裕司
    日本食品科学工学会北海道支部大会  2017/02
  • 機械工学をベースとした環境エネルギー技術の開発  [Invited]
    村井祐一
    都城高専 機械工学科特別講演会  2016/12
  • Bird shadow imaging coupled with wire-frame model analysis for automatic bird species identification  [Invited]
    Y.Murai, Y.Takeda, H.Kumeno
    2nd Meeting of Workgroup of Birdstrike Science and Engineering  2016/10
  • Multi-polar vortex dynamics of dispersion-induced flow control  [Invited]
    Y.Murai
    China Sympoisum on Multiphase Flow Measurement  2016/09
  • 世界と共同開発、流体力学から湧き出るアイデアの実用化  [Invited]
    村井祐一
    北海道青少年科学文化財団公開講座  2016/03
  • Frictional drag reduction by small bubbles versus large bubbles  [Invited]
    Y.Murai, Y.Tasaka, H.Park
    Workshop on Transition Control in Dispersed Flows  2016/01
  • Measurement-based discovery on new function of microbubbles in fluid flow  [Invited]
    Y.Murai
    Internatioal Forum on New Horizons in Multiphase Flow Measurement  2015/12
  • マイクロバブルの最前線  [Invited]
    村井祐一
    函館高専 先端科学技術講演会  2015/12
  • 科学するこころ  [Invited]
    村井祐一
    石川高専オープンカレッジ講演会  2015/11
  • 夢を追いかけてー自然・人との調和をめざす未来の研究ー  [Invited]
    村井祐一
    石川高専創立50周年記念事業記念講演会  2015/11
  • 超音波ドップラーレオメトリーの開発  [Invited]
    村井祐一
    化学工学会第47回秋季大会  2015/09
  • Microbubble-liquid interaction observed in channel flows from laminar, transition, and turbulent regimes  [Invited]
    Y.Murai, Y.Tasaka, Y.Oishi (keyno
    ASME International Conference on Nano, Micro, and Minichannels  2013
  • Fundamentals in frictional drag reduction by bubble injection  [Invited]
    Y.Murai (k
    International Conference on Multiphase Flow 2013  2013
  • Paradigm shift in modern flow measurement and gas flow metering  [Invited]
    Y.Takeda, Y.Murai
    International Gas Research Conference - Korea  2012
  • Broad destruction of density stratification using a single bubble plume  [Invited]
    Y.Murai, H.Kayukawa, Y.Tasaka, I.Kumagai, H.Kitaura
    Japan-US Seminar on Two-Phase Flow Dynamics - Tokyo  2012
  • Particle Tracking AccelerometryによるPIVの粒子追従性問題からの解放  [Invited]
    村井 祐一
    JAXA第4回EFD/CFD融合ワークショップ  2011
  • マイクロバブルが乱流渦の成長を選択的に鎮圧する現象について  [Invited]
    村井 祐一
    日本混相流学会年会講演会2011京都  2011
  • 単視点型カラートモグラフィック３次元ヴォクセルPIV  [Invited]
    村井祐一, 田坂裕司, 武田 靖, 神田哲志(keyno
    第87期日本機械学会流体工学部門講演会  2009
  • 超音波パルスによる二相流動場の高精細計測 ～ 光計測に優る点  [Invited]
    村井 祐一(k
    第12回オーガナイズド混相流フォーラム  2008
  • Backlight imaging tomography applied to slug flows in straight and helical tubes  [Invited]
    Y.Murai, Y.Takeda, F.Yamamoto
    5th Int. Symposium on Measurement Techniques for Multiphase Flows  2006
  • 再帰型相互相関PIVによるエアレーション流動場の高精細計測  [Invited]
    村井祐一, 程 文, 笹木俊男, 山本富士夫
    日本混相流学会年会講演会2005  2005
  • Turbulent Shear Stress Profiles in a Horizontal Bubbly Channel Flow  [Not invited]
    Y.Murai, Y.Oishi, T.Sasaki, Y.Kodama, F.Yamamoto
    6th International Symposium on Smart Control of Turbulence  2005
  • Experimental Study on Bubble Behavior Contributing to Frictional Drag Reduction  [Invited]
    Y.Murai, H.Oiwa, Y.Ooishi, F.Yamamoto
    U.S.- Japan Workshop on Microbubble Friction Drag Reduction  2003
  • Application of Particle Tracking Velocimetry to Multiphase Flows - New Finding with It  [Not invited]
    Y.Murai, F.Yamamoto(keyno
    Int. Symp. Optical Methods and Image Processing in Fluid Flow Measurement,ASME/FED & JSME Joint Fluids Conferenc  2003
  • 気泡流の微細流動構造,その CFD と EFD [基調講演]  [Invited]
    村井 祐一
    日本機械学会第76期流体工学部門講演会  1998
  • 気泡流の CFD 予測と PIV 計測 [招待講演]  [Invited]
    村井 祐一
    第１回オーガナイズド混相流フォーラム  1997

Association Memberships

  • American Physics Society   THE JAPAN SOCIETY OF MECHANICAL ENGINEERS   THE VISUALIZATION SOCIETY OF JAPAN   日本流体力学会   日本混相流学会   Institute of Physics   

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2027/03 
    Author : 田坂 裕司, PARK HYUNJIN, 柳澤 孝寿, 堀本 康文, 村井 祐一
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2021/04 -2026/03 
    Author : 村井 祐一, 田坂 裕司, PARK HYUNJIN, 熊谷 一郎, 堀本 康文, 北川 石英, 大石 義彦
     
    令和３年度は，以下の研究調査を進めた．一次元ボイド波伝播モデルによるPBIの適用距離の予測(朴)，３次元翼による微細気泡発生法と正味摩擦抵抗低減効果の検討（熊谷）， 高時間分解レーザーせん断応力計の開発とVITA法適用による統計評価（大石），空気充填ディンプルに形成される気膜の計測とマイクロ気膜法に関する予備調査（北川），非定常剪断流れにおける分散混相流体の実効粘度（田坂），高Reynolds数Taylor-Couette乱流の速度計測と抵抗低減（堀本），水平チャネルにおいて大型気泡群を有する2相乱流流動の直接数値シミュレーション（村井），傾斜チャンネル内の境界層で挙動する気泡抗力係数算定（村井）．間欠的気泡注入による抵抗低減効果の長距離持続化（朴），水平チャネルのボイド率急変時の乱流境界層構造のステップ応答の計測（村井）． これらの成果は抵抗低減における気泡運動の流体力学について IJMFに4偏，気泡を含む応力場の計測技術について Exp Fluidsに4偏，船舶抵抗低減の実スケール実験について Ocean Engに2編，気泡流の非線形流体力学について JFMに1編，その他を含めて計18編の学術雑誌に掲載された．本課題で主柱としている下記の3項目について，初年度としての進展のうち特筆すべきものに以下が挙げられる．[PBI] 気泡分布の時空間パターン制御について，船底ボイド波のKdV-Burgers方程式によるデータ解析から現象相似性が発見された．[HBC] 水中翼による局所減圧型の境界層気泡分布制御法の開発では，微細気泡分散状態とエアキャビティ状態のモード変換機構が解明された．[RMF] 超音波と光による実時間フィードバック制御の開発では，複雑せん断流体の実効粘度の周波数依存性を計測する技術が確立された．
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2022/04 -2025/03 
    Author : 北川 石英, 高木 知弘, 外岡 大志, 村井 祐一, 渡村 友昭
     
    抵抗低減・伝熱促進・反応促進技術では，壁面近傍での分散体のサイズ・挙動・分布構造が機器性能に直接的影響を与える．本研究では，濡れ性操作によって表面の機能化を図り，分散体挙動・分布構造を自在に制御することを目的として，スケールの異なる４つの流れ場，流場①「マイクロチャネル流れ」，流場②「界面衝突流れ」，流場③「水平チャネル流れ」，流場④「テイラークエット流れ」を対象とした調査を実施した．その結果，流場①では，親水性・疎水性部分をマイクロパターニングしたガラス基板上で微小な水滴がアレイ状に形成されることを確認した．流場②では，実験に対して，固定された物体後流の遷移が過去の文献で示された結果と定性的に一致することを確認し，数値計算に対して，複数の相を取り使うことが可能な multiphase-field 法を構築した．流場③では，機能表面を利用した移流気泡群の一方向輸送実験を行い，撥水面を二分割することにより，高レイノルズ条件下での気泡輸送率の向上に成功した．最後に，流場④では，テイラークエット流れ場に気体を注入した場合の移流・拡散プロセスの計測を行い，高速移流気泡群と集積定在気泡群の2つが共存する気液二相流を実現した．
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2022/04 -2025/03 
    Author : 北川 石英, 高木 知弘, 外岡 大志, 渡村 友昭, 村井 祐一
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2021/04 -2025/03 
    Author : 正信 聡太郎, 村井 祐一, 高野 慧, 山本 マルシオ
     
    海洋鉱物資源開発においては揚鉱ユニットが技術的な中核を担う。揚鉱ユニットの設計及び運用においては、揚鉱管・移送管内のフローアシュアランス（流路保全）分析が必須であるが、管の傾斜や動揺等を考慮した非定常の固液二相流に対するリアルタイム分析技術がないため一連の技術開発を遅延させている。そこで本研究では、超音波計測技術を独自開発し、管内を脈動する固液二相流の流動状況と圧力損失の周波数スペクトル空間での因果関係を解明してフローアシュアランス分析に適用可能な圧力損失推定手法を構築する。さらに、圧力損失を低減可能な制御デバイスを開発するとともに、内部流との相互作用が分析できる水中線状構造物の応答予測手法を構築する。 当該年度は、以下の課題を実施した。 【①圧力損失推定技術の開発】 鉛直管を対象とした脈動流中における時間領域圧力損失推定プログラムの基本アルゴリズムを検討するとともに、過去に構築した定常状態での圧力損失推定手法を用いて、移送管の形状変化が圧力損失に及ぼす影響を調査して、試設計した移送管に対する最適な移送条件（固相体積濃度、平均流速）を設定した。2022年度に実施を計画している、口径25Aの円管を鉛直から水平まで傾斜可能な固液二相流の移送実験計画を策定するとともに、当該実験装置を製作した。さらに、2022年度に検討予定であった口径80Aの円管を用いた移送実験計画も前倒して策定した。また、管内を流動する粗大粒子を位置特定して計数する超音波エコーグラフィの計測技術について基本信号処理アルゴリズムを開発した。 【②圧力損失最小化技術の開発】 超音波スピニングレオメトリー(USR)により固体粒子懸濁液のレオロジーの計測を実施した。 【③水中線状構造物の応答予測手法の開発】 内部流を考慮しない水中線状構造物挙動の応答予測プログラムを開発した。
  • Development of ultrasonic multiphase flow measurement techniques
    JOGMEC：
    Date (from‐to) : 2020/04 -2023/03
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    Date (from‐to) : 2019/04 -2023/03 
    Author : 田坂 裕司, PARK HYUNJIN, 村井 祐一
     
    ①混相流体の局所非定常レオロジー物性の評価，②実効乱流渦粘度の評価，③気泡集積と渦の安定性評価，④局所乱流塊と気泡の干渉，を個別プロジェクトとして設定し研究を進めた． ①に関して，これまでに構築した超音波スピニングレオメトリ（USR）を用いて，非ニュートン流体に粒子が混入した場合の実効粘度および実効弾性の変調を評価し，理論的な考察を加えた．これらの結果は論文にまとめられ掲載された．またUSRを拡張し，のこぎり波など自由な加振モードに対応するため，のこぎり波がフーリエ変換によりいくつかの周波数成分に展開されることから，複数の周波数成分を持つ振動を加えた場合の方法論を構築した． ②に関して，レイノルズ方程式を基準の運動方程式として用いることで，実効渦粘度を評価するアルゴリズムを構築した．また，これを用いた評価を行うための計測装置として，小型のテイラー・クエット流れとそこにマイクルバブルを含む水を導入するための装置考案した． ③移流しながらの渦による気泡の集積挙動とその渦への影響を調べるため，ラインスキャンカメラを用いた新たな計測法を開発し，気泡チャネル流の装置を用いてその性能を検証した． ④円管内に生じる局所乱流塊である，乱流パフの形成・減衰挙動を，乱流塊とともに移動するカメラによるラグランジュ計測により捉えた．可視化結果から形成過程に現れる特徴的な振る舞いを抽出し，次年度に定量化実験を行うためのパラメータ領域を明瞭にした．また，管壁に設置した出っ張りが乱流塊に及ぼす影響を調査し，条件によっては流れを乱すのではなく，乱流塊を減衰させ，流れを再層流化に導くことを示した．
  • Ultrasonic surface temperature measurement
    三菱重工業株式会社：
    Date (from‐to) : 2020/08 -2022/03
  • Micro wind turbine for pipeline facilities
    東京ガス株式会社：
    Date (from‐to) : 2020/07 -2022/03 
    Author : 村井祐一,朴炫珍,堀本康文,田坂裕司
  • 日本学術振興会：科研費：国際共同研究強化B
    Date (from‐to) : 2018/10 -2022/03 
    Author : 村井 祐一
  • Flow visualization and velocity profiling of milk-based product
    雪印メグミルク株式会社：
    Date (from‐to) : 2018/07 -2021/03 
    Author : 村井祐一, 朴炫珍, 芳田泰基, 田坂裕司
  • 日本学術振興会：科研費 基盤研究(A)
    Date (from‐to) : 2017/04 -2021/03 
    Author : 村井祐一
  • Ultrasonic pulse multiphase flowmeter having flow monitoring functions
    NEDO：先導研究プログラム
    Date (from‐to) : 2019/06 -2020/10 
    Author : 村井祐一,田坂裕司,朴炫珍
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/04 -2020/03 
    Author : Kumagai Ichiro
     
    As an Earth-friendly tool, we invented a hydrofoil bubble generator to reduce ship drag and conducted experiments using a high-speed channel tunnel in National Maritime Research Institute (NMRI) to understand the behaviors of air bubble generation at a cruising speed up to 20 knots. The threshold of air entrainment, the air flow rate, and the bubbly flow pattern depend on Reynolds number, angle of attack, and hydrofoil type. We identified intermittent air entrainment at a low-speed condition, stable air entrainment, and air entrainment with a ventilated cavity at a high-speed condition (> 5m/s). Although the ventilated cavity lowers the ability of air entrainment, a large volume of air bubbles (50 l/min) was generated by the hydrofoil system at 9 m/s, which has a high potential to reduce ship drag. We have also conducted a towing tank experiments using a 400m tank in NMRI and obtained the maximum net drag reduction (about 12%) for a 36m model ship at a cursing speed (10 knots).
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2019/03 
    Author : Tasaka Yuji, NAKANO Naoto, PEIXINHO Jorge, BOX Finn, MULLIN Tom
     
    The present study investigated subcritical flow transitions in a pipe with hair-pin vortices as disturbances generated by a synthetic jet actuator, which is capable to control amplitude, frequency and number of the hair-pins. The experimental results indicated that the frequency and amplitude do no affect considerably the transition, but for small number of hair-pins, the transition clearly depends on the number of vortices. As other project in the study, trials to modify self-sustaining process of the local turbulence were performed by, for example, attachment of a bubble on the pipe wall. It works well to introduce relaminarization of the local turbulence and corresponding mechanism we considered is removing inflection points on the velocity profile at the trailing edge of the turbulence by flow winding and slip on the bubble surface.
  • マイクロバブルの乱流境界層中への混入による摩擦抵抗の低減
    防衛装備庁：安全保障技術研究推進制度
    Date (from‐to) : 2016/09 -2018/03 
    Author : 村井祐一
  • 日本学術振興会：科研費 挑戦的萌芽研究：
    Date (from‐to) : 2015/04 -2017/03 
    Author : 村井 祐一
  • JSPS：GAR - Kiban (A)
    Date (from‐to) : 2012/04 -2017/03 
    Author : Yuichi MURAI
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013/04 -2016/03 
    Author : Tasaka Yuji, MURAI Yuichi
     
    We studied process and condition of transition to a turbulent puff that is local turbulence observed in a pipe flow as catastrophic flow transition to turbulence. (1) A fine pipe flow facility with 8 m in the pipe length and 32 mm in the inner diameter of pipe that realizes laminar flow for more than 25,000 of Reynolds number without perturbation was constructed. (2) Novel visualization technique was established to extract vortical structure in a puff effectively. Through experiments, (3) complex edge of turbulence that was found by our previous study was represented in this system and physics embedded in the complex edge was elucidated, and further, (4) influence of adding microbubbles into pipe flows were investigated statistically: turbulent puffs were stabilized by adding bubbles.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013/04 -2016/03 
    Author : Kumagai Ichiro, MURAI Yuichi, TASAKA Yuji
     
    Fluid experiments on buoyancy-driven flows in deformable gel beads layer were conducted to understand the dynamics of magma transport in a partially molten region. As an analogue material of partially molten media, a mixture of transparent hydro gel beads and viscous fluids was used. Our experimental results indicate that the intermittent nature of the volcanic activity is inherent to magma transport in a partially molten zone, which explains the spatio-temporal patterns of volcanic activity.
  • 風車の長期的設計指針を決めるランドマークデザイン
    JSPS：GAR - Challenge
    Date (from‐to) : 2011/04 -2013/03 
    Author : Yuichi MURAI
  • NEDO：ITRDP
    Date (from‐to) : 2008/06 -2012/05 
    Author : Yuichi MURAI
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2011 -2012 
    Author : TASAKA Yuji, MURAI Yuichi
     
    In order to improve efficiency of frictional drag reduction technique by injecting bubbles, we investigated flow of bubble mixture and developed measurement system for efficient flow control. Experimental investigations in a bubbly channel flow suggested basic mechanism of bubble clustering from a point of view of bubble-bubble interactions. We also developed a monitoring tool of flows and bubbles using ultrasonic wave. Applicability of the tool for actual vessels was discussed.
  • Large Flow Rate Type Bubble Generator
    Date (from‐to) : 2008 -2012
  • 複素粘度解析によるマイクロバブル流体の不可説明要因の一掃
    JSPS：GAR - Kiban (B)
    Date (from‐to) : 2009/04 -2011/03 
    Author : Yuichi MURAI
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2008 -2010 
    Author : FUTAKAWA Masatoshi, HASEGAWA Shoichi, KANEKO Akiko, HAGA Katsuhiro, KOGAWA Hiroyuki, IDA Masato, NAOE Takashi, MATSUMOTO Yoichiro, OKITA Kohei, TANAKA Nobuatsu, TAKEMURA Fumio, OKAMOTO Koji, MURAI Yuichi
     
    The purpose in this study is the development of the practical protection technologies for mitigating the pressure waves by the microbubble injection in the liquid mercury spallation neutron source. We investigated the mitigation technologies from the viewpoints of microbubble injection, pressure wave propagation in bubbly liquid, bubble-bubble interaction, and pitting damage. As results, we developed the technique to mitigate the cavitation damage, which becomes barrier to realize the MW-class spallation target.
  • NEDO：ITRDP
    Date (from‐to) : 2005/07 -2008/06 
    Author : Yuichi MURAI
  • JSPS：GAR - Wakate (B)
    Date (from‐to) : 2005/04 -2008/03 
    Author : Yuichi MURAI
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2006 -2008 
    Author : TAKEDA Yasushi, MURAI Yuichi, TASAKA Yuji
     
    気流の空間的構造を定量計測するPIV(Particle Image Velocimetry)を技術開発することを目的とし3年間の研究の実施を通じて多面的な成果を上げた. 大規模な気流計測における主要な問題は, 環境負荷の少ないトレーサを開発すること, ならびに三次元非定常構造を定量捕獲するための光学設計, さらには速度ベクトルデータの高密度化であった. 平成18年度は, トレーサの開発としWatermist法, Soap Bubble法, ならびにTuft Resonance法について検討を行い, さらにPIVに適合したトレーサの注入方法を設計・検定した. これと同時に300m規模の大気流動場を三次元計測する問題点提起実験を実施した. 平成19年度は開発したトレーサ注入法と光学系を実例計測によりデモンストレーション実験した. 計測対象は竜巻のPIV計測, 樹木や鉄塔をモデル化した透過性物体の周囲空間流動のPIV計測である. 平成20年度は大気ダウンバーストを室内モデル実験置換し, カラートモグラフィックPIV技術の実証実験を実施した. これらの開発の結果, 従来まで低密度データの2次元計測に制約されてきた気流構造計測が, 3次元高密度データ取得が可能となるに至った. また応用実験から気流のもつ固有の流動場が新たに発見され, これらについてのダイナミクスを論文等で発表した.
  • 光・画像計測を応用した気液二相壁面乱流の特徴抽出に関する研究
    MEXT and JNC：ABER
    Date (from‐to) : 2003/09 -2006/03 
    Author : Yuichi MURAI
  • 気泡による高速せん断乱流のコントロール
    JSPS：GAR - Wakate (A)
    Date (from‐to) : 2003/04 -2006/03 
    Author : Yuichi MURAI
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : YAMAMOTO Fujio, MURAI Yuichi
     
    The present research has been carried out to construct a system of PIV (Particle Image Velocimetry) as a parallel computing station, and has been applied to analyze turbulent structures in multiphase flows. As a result, the following remarks were concluded ; A. Concerning construction of PIV parallel computing station : A-1 After we developed a new hybrid system of PIV and CFD which was a combined system consisting numerical analysis technique for solving Navier Stokes equation and VGT (Velocity Gradient Tensor technique for PTV, it was confirmed that the hybrid system could compute the pressure field around a Savonius type of wind turbine. A-2 Bubble-bubble interaction in bubbly flows were discussed with 3-D PTV. It was made clear that attractive forces were acted in the vertical direction and exclusive forces were acted in the horizontal direction. A-3 A new inverse analysis has been devised and applied to bubbly flows at high void fraction, and then a new technique for computing liquid phase flow field from PIV/PTV measurement using the inverse analysis has been developed. B. Concerning analysis of turbulent structure of gas-liquid two-phase flows : B-1 A new system for synchronizing a high speed high resolution vide camera and a shear stress sensor was constructed, and the friction drag modification mechanisms in wall sliding bubbly flows were elucidated with PIV measurement results. B-2 Effective viscosity, turbulent flow characteristics and additional viscosity were discussed in Taylor-Couette bubbly flows in a gap between coaxial double circular cylinders, and then the transition phenomenon from ring vortex to spiral vortex was visualized and discussed. B-3 Reynolds stress distribution in boundary layers of gas-liquid two-phase flows close to the flat wall was measured using a new shallow focal PTV system, and consequently the relation between Reynolds stress and friction drag reduction in the boundary layer of the two-phase flow was discussed. B-4 In order to elucidate the turbulent structures of bubbly flows and slug flows in a helical coil tube, a new CT image measurement system was developed. As a result, formation of secondary flows due to the centrifugal force effects on the two-phase flows and bubble distribution were newly found and discussed. All the above results were published as 25 papers in the academic journals described in the references
  • Application of Ultrasonic Doppler Velocimetry
    Date (from‐to) : 2003
  • 分散性混相流における乱流構造の解明とその応用技術の提案
    JSPS：FRP
    Date (from‐to) : 2001/03 -2002/03 
    Author : Yuichi MURAI
  • CFDとPIVを併用した固気液三相流の高精細解析
    MEXT：Promotion (A)
    Date (from‐to) : 1999/04 -2001/03 
    Author : Yuichi MURAI
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1998 -2000 
    Author : YAMAMOTO Fujio, MURAI Yuichi, OHTA Junichi
     
    Investigation of micro-mechanism of flow fields becomes important in the research of environmental pollution, chemical reaction, micro-gravity devices, semiconductors, and biotechnology. Our group has been focussing on development of Particle Image Velocimetry (PIV) in order to elucidate the detailed structure of various type flows. In the period of the present project, three main advances have been achieved as follows. Yamamoto developed brand new algorithm for PIV using Dellaunay tesselation particle tracking method, velocity gradient tensor particle tracking method, and Fuzzy logic based particle tracking method. Computation speed is much improved with revision of trackability in highly deformed flow field. Ohta succeeded in measuring micro-scale flow structure in the flow driven by surface tension, turbulent jet flow, and particulate flow. Resolution of PIV is evaluated by comparing the data with Laser Doppler Velocimeter, In-line Holographic PIV.Murai developed the application method of PIV to multiphase flows, and highly accurate post-processing algorithm for Particle Tracking Velocimetry. Microscopic structure of turbulence in bubbly flow could be captured by combination of PIV and the post-processing.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1996 -1998 
    Author : KOBAYASHI Toshio, TAKAGI Shu, OSHIMA Mari, SAGA Tetsuo, TANIGUCHI Nobuyuki
     
    An aim of this research was to develop models for a large eddy simulation (LES) of multiphase turbulence flow with dispersed particles and to evaluate and optimize them using numerical simulation. For modeling of multiphase flows, a direct numerical simulation (DNS) of bubble motions evaluated their effects on the fluid flow and the interaction between bubbles. Turbulence variation by small solid particles was also investigated. For evaluating a formulation of particle motions in the LES, a Lagrangian equation and a statistical averaged equation were compared by the numerical examinations. The numerical method of LES was developed based on the former model. These results were validated in views of the particles and the fluid flows using data of DNS and experiment with visualization techniques. For some basic flows, as mixing layers, jets, channel flows, the above models and the methods were examined in the range from laminar to turbulence, to indicate an universal information for the bubbly flow and the particle-laden air flow as follows, a) Particle size effects on the bubble motions by the buoyancy forces and the turbulence could be analyzed by the LES including the precise model of the bubble motion and its contribution to the volume averaged equation. b) The turbulence dissipation by the solid dispersed particles could be evaluated by a subgrid-scale model including the particle-fluid interaction, while a grid-scale interaction was not simulated by the present model effectively enough. These results validated the feasibility of LES to the dispersed-particle multiphase flows and indicated that the temporal and the spatial scales of the turbulence and the particle motion should be considered for the modeling of the particle-fluid interaction and its optimization.
  • Study on Turbulent Frictional Drag Reduction
    Date (from‐to) : 1998
  • Innvation of wind power generation technology
    Date (from‐to) : 1998
  • 気泡流乱流中の微細流動構造の数値解析・画像解析
    文科省：科研費 奨励研究(A)
    Date (from‐to) : 1996/04 -1997/03 
    Author : 村井 祐一
  • 気液二相流の微細構造シミュレーション
    JSPS：DC1
    Date (from‐to) : 1995/04 -1997/03 
    Author : Yuichi MURAI
  • Development of PIV system
    Date (from‐to) : 1992
  • Multiphase Science and Technology
    Date (from‐to) : 1988

Industrial Property Rights

  • 特願特願2022-139196:食品検出装置および食品検出方法  2022年/09/01
    岸田哲明, 舟橋治幸, 藤井智幸, 朴炫珍, 村井祐一, 田坂裕司  雪印メグミルク株式会社
  • 特願特願2022-011110:流体流通システム  2022年/01/27
    日野将人, 鳥海良一, 相澤 望, 村井祐一, 田坂裕司, パクヒョンジン, 堀本康文, 梅村崇弘  東京ガス株式会社
  • 特願特願2022-011109:Turbine and fluid supply system  2022年/01/27
    日野将人, 鳥海良一, 相澤 望, 村井祐一, 田坂裕司, パクヒョンジン, 堀本康文, 梅村崇弘  Tokyo Gas Co., Ltd.
  • 特願2019-056493:非接触型レオロジー物性計測装置、システム、プログラムおよび方法  2019年/03/25
    田坂裕司, 芳田泰基, 村井祐一
  • CP2929823:Object detection apparatus, objection detection method, and object detection system  
    Canadian Patent
  • 特許 日本:第5532220号:高効率船体摩擦抵抗低減システム    2014/05/04
  • 特許 日本:第5501028号:回転翼式気泡発生装置    2014/03/20
  • 特許 日本:第5208124号:超音波混相流量計，超音波混相流量計測プログラム，および超音波を用いた混相流量計測方法    2013/03/01
  • 特許 米国:No. US7500837B2:Small size gear pump    2009/03/10
    Yuichi MURAI
  • 特許 日本:第4245997号:小形ギアポンプ    2009/01/16
    宮城直樹, 村井祐一, 宮崎孝司, 青柳裕治, 松井多志
  • 特許 日本:第4070385号:摩擦抵抗低減船    2008/01/25
    高橋義明, 村井祐一
  • JP6379343:物体検出装置，物体検出方法および物体検出システム  
  • JP6183703:物体検出装置，物体検出方法および物体検出システム  
  • KR10-1900176:Object detection apparatus, objection detection method, and object detection system  
    Korean Patent
  • US9721154:Object detection apparatus, objection detection method, and object detection system  
    United States, Pa
  • TWI604415:Object detection apparatus, objection detection method, and object detection system  
    Taiwanese Paten
  • TWI586992:Object detection apparatus, objection detection method, and object detection system  
    Taiwanese Paten
  • US678941B2:Friction reduction ship and method for reducing frictional resistance  
    US Patent
  • JP5072053:飛来物探査装置および映像取得手段の設置方法  
  • JP5059666:飛来物検知装置、飛来物検知方法およびコンピュータプログラム  
  • US8401805:Ultrasonic multiphase flowmeter, ultrasonic multiphase flow rate measurement program, and multiphase flow rate measurement method using ultrasonic wave  
    United States, Paten

Social Contribution

  • 泡が地球温暖化を抑える
    Date (from-to) : 2017/07
    Role : Demonstrator
    Sponser, Organizer, Publisher  : 東京国立科学博物館 機械学会賞受賞記念長期出典

Media Coverage

  • 船舶の研究と防衛技術の関係
    Date : 2017/01
    Publisher, broadcasting station: TBSニュース23
    Media report
  • 船舶の高速化技術
    Date : 2016/09
    Publisher, broadcasting station: NHK クローズアップ現代
    Media report
  • 小型風力発電システム
    Date : 2011/07
    Publisher, broadcasting station: NHK おはよう日本
    Media report
  • 船舶の気泡による省エネ
    Date : 2009/12
    Publisher, broadcasting station: 日経新聞
    Paper
  • 回らない風力発電
    Date : 2009/06
    Publisher, broadcasting station: 北海道テレビ放送(HTB) ニュース
    Media report
  • 札幌市における台風被害
    Date : 2007/09
    Publisher, broadcasting station: 北海道テレビ放送(UHB)ニュース解説
    Media report
  • アート風力発電
    Date : 2001/05
    Publisher, broadcasting station: NHK サイエンスゼロ
    Media report
  • 船舶の省エネ技術
    Date : 2000/07
    Publisher, broadcasting station: ラジオ番組（FTV)
    Media report
  • ナオトカ号重油流出事故対応
    Date : 2000/01/07
    Others

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