Researcher Profile and Settings

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

Affiliation

• Japan Agency for Marine-Earth Science and Technology, Data Science Research Group, Volcanoes and Earth’s Interior Research Center (VERC), Research Institute for Marine Geodynamics (IMG), Guest researcher

Profile and Settings

• Name (Japanese)

  Tasaka

• Name (Kana)

  Yuji

• Name

  201301066787063235

Alternate Names

https://lfc-me.eng.hokudai.ac.jp/index-en.html

Affiliation

• Japan Agency for Marine-Earth Science and Technology, Data Science Research Group, Volcanoes and Earth’s Interior Research Center (VERC), Research Institute for Marine Geodynamics (IMG), Guest researcher

Achievement

Research Interests

• 実験流体力学   流れの安定性   熱対流   Rheometry   液体金属流れ   超音波計測   

Research Areas

• Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Fluid engineering

Research Experience

• 2024/03 - Today Hokkaido University Laboratory for Flow Control, Division of Mechanical & Aerospace Engineering, Faculty of Engineering Professor
• 2022/04 - Today Japan Agency for Marine-Earth Science and Technology Data Science Research Group, Volcanoes and Earth’s Interior Research Center (VERC), Research Institute for Marine Geodynamics (IMG) Guest researcher
• 2011/02 - 2024/03 Faculty of Engineering, Hokkaido University Associate Professor
• 2017/04 - 2017/07 Université du Havre Laboratoire Ondes et Milieux Complexes Visiting Researcher
• 2016/10 - 2017/01 Helmholtz Zentrum Dresden-rossendorf Group of Magnetohydrodynamics Guest scientist
• 2007/04 - 2011/01 Faculty of Engineering, Hokkaido University Assistant Professor
• 2008/04 - 2009/01 School of Physics and Astronomy, The University of Manchester Visiting Research Fellow
• 2005/04 - 2007/03 Graduate School of engineering, Hokkaido University Research Associate

Education

• 2000/04 - 2005/03  Hokkaido University  Graduate School of Engineering  Division of Mechanical Science

Awards

• 2024/07 一般社団法人可視化情報学会 第３５期可視化情報学会学会賞（技術賞）
   超音波パルスエコグラフィーによる管内混相流モニタリング技術 

  受賞者: 朴炫珍;田坂裕司;村井祐一
• 2023/07 一般社団法人日本機械学会 流体工学部門フロンティア表彰
  
• 2021/11 社団法人日本機械学会 流体工学部門貢献表彰
  
• 2020/08 可視化情報学会 第31期可視化情報学会 学会賞（論文賞）
   Vortex tracking on visualized temperature fields in a rotating Rayleigh-Benard convection 

  受賞者: 能登大輔;田坂裕司;朴炫珍;柳澤孝寿;村井祐一
• 2020/08 日本混相流学会 2019年度日本混相流学会賞 論文賞
   気液二層乱流中に発生する気泡クラスタリングの実験的解明 

  受賞者: 大石義彦,田坂裕司,村井祐一
• 2019/06 Elsevier Outstanding contribution in Reviewing (Flow Measurement and Instrumentation)
   

  受賞者: Yuji Tasaka
• 2018/09 可視化情報学会 第29期可視化情報学会 学会賞（技術賞 カテゴリI）
   超音波パルスドップラーによる食品物性の定量可視化技術 

  受賞者: 芳田泰基;田坂裕司;朴炫珍;村井祐一
• 2017/04 日本機械学会 2016年度日本機械学会賞（技術）
   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 

  受賞者: 村井祐一;熊谷一郎;田坂裕司;朴炫珍;高橋義明
• 2016/02 Elsevier Outstanding reviewer (Flow Measurement and Instrumentation)
   

  受賞者: Yuji Tasaka
• 2015/08 日本混相流学会 2014年度日本混相流学会賞 奨励賞
   超音波流速分布計を用いた微細気泡を含む流体の実効粘度評価 

  受賞者: 田坂裕司
• 2014/07 可視化情報学会 第25期可視化情報学会 学会賞（論文賞）
   Development of ultrasonic visualization for capturing the characteristics of viscoelastic fluids 

  受賞者: 白鳥貴久;田坂裕司;村井祐一;武田靖
• 2014/07 日本混相流学会 2013年度日本混相流学会賞 技術賞
   超音波流速分布測定法（UVP）の混相流計測への拡張に関する技術開発 

  受賞者: 村井祐一;田坂裕司;武田靖
• 2012/08 日本混相流学会 2011年度日本混相流学会賞 論文賞
   船舶の抵抗低減の実用化・普及に向けた低負荷気泡発生機構の研究 

  受賞者: 熊谷一郎;村井祐一;田坂裕司
• 2010/07 日本混相流学会 2009年度日本混相流学会賞 論文賞
   気泡による摩擦抵抗低減メカニズム解明のための二相乱流構造計測 

  受賞者: 大石義彦;村井祐一;田坂裕司;武田靖

Published Papers

• Inline estimation of volume fraction in Newtonian emulsions based on ultrasonic velocity profiling viscometry

  Wenqing Zheng, Yuji Tasaka, Kohei Ohie, Yuichi Murai

  Measurement Science and Technology 35 125305  0957-0233 2024/09/10 [Refereed][Not invited]
   

  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%.
• Cost-effective production of density-controllable monodisperse spheres for experiments in fluids

  Kohei Ohie, Daigo Nishizuka, Taiki Yoshida, Yuji Tasaka

  Physics of Fluids 36 (9) 1070-6631 2024/09/01 [Refereed][Not invited]
   

  Cost-effective production method for making density-controllable monodisperse spheres is demonstrated. A sodium alginate aqueous solution containing gelatin is emulsified with canola oil. The droplet surface is covered with a calcium alginate membrane by dropping the emulsion into a calcium lactate aqueous solution. The content of the canola oil can control the sphere's density. To demonstrate the applicability of the spheres to experimental research, rheological measurements of the suspensions of the spheres were performed. The effective viscosity agrees with the theoretical formula at volume fractions of 0.7%–11.7%. The demonstration highlights that the spheres can function as neutrally buoyant solid particles in studies for the physics of fluids.
• Coupling a torque rheometer with an ultrasonic velocity profiler for evaluating multiphase fluids in oscillatory shear flows

  Kohei Ohie, Taiki Yoshida, Yuji Tasaka

  Journal of Rheology 68 (5) 665 - 678 0148-6055 2024/07/22 [Refereed][Not invited]
   

  We propose a torque rheometer coupled with an ultrasonic velocity profiler (UVP) for evaluating multiphase fluids as bulk rheology in oscillatory shear flows. The rheometer mainly consists of wide-gap coaxial cylinders, where the outer cylinder is sinusoidally oscillated and the inner cylinder is fixed to a torque sensor for measuring the wall shear stress. Based on Cauchy’s equation of motion, the spatiotemporal distribution of the shear stress is obtained from the velocity information and the wall shear stress as a boundary condition. This rheometer was applied to a carboxymethyl cellulose aqueous solution and compared with a standard torque-type rheometer. The results of the evaluated viscoelastic properties agreed well with each other, indicating the validity of the proposed rheometry. To further investigate the applicability of the rheometer to multiphase fluids, suspensions of solid spherical particles with a diameter of 220μm with volume fraction of 0.8–3.4% were measured, which are out of the applicable ranges of the standard rheometer. For volume fractions up to 3% where the UVP measurement is available, the relative viscosity agrees well with a theoretical formula. This indicates the applicability of the method to examine multiphase fluids.
• Hydraulic Transport of Large Solid Particles in Inclined Pipes under Pulsating Flow Conditions

  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.
• Rheological evaluation of suspensions under unsteady shear

  Yuji Tasaka, Kohei Ohie, aiki Yoshida, Yuichi Murai

  Nagare 43 154 - 160 2024/06 [Not refereed][Invited]
  
• Experimental and theoretical fluid dynamics of spherical Savonius turbines operated in pipe flows

  Yuichi Murai, Takahiro Umemura, Hyun Jin Park, Yasufumi Horimoto, Yuji Tasaka

  Journal of Fluids and Structures 2024/06
• Wall shear stress measurement of turbulent bubbly flows using laser Doppler displacement sensor

  Yoshihiko Oishi, Sho Onuma, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hideki Kawai

  Flow Measurement and Instrumentation 96 102546 - 102546 0955-5986 2024/04 [Refereed][Not invited]
  
• Rheology of dilute bubble suspensions in unsteady shear flows

  K. Ohie, Y. Tasaka, Y. Murai

  Journal of Fluid Mechanics 2024/03/25
• Function of the turbo‐sail airfoil applied to the Darrieus wind turbine

  Yoshimichi Ono, Ryosuke Sayama, Yuichi Murai, Hyun Jin Park, Yuji Tasaka

  Wind Energy 1095-4244 2024/02/17 [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.
• On the rotation of a Savonius turbine at low Reynolds numbers subject to Kolmogorov cascade of turbulence

  Shūji Ōtomo, Yuji Tasaka, Petr Denissenko, Yuichi Murai

  Physics of Fluids 2024/02/01 [Refereed][Not invited]
  
• Bubble clustering in turbulent boundary layer on a moving wall utilizing belt-driven system

  Yasufumi HORIMOTO, Itsuki MORI, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI

  Journal of Fluid Science and Technology 19 (2) JFST0013 - JFST0013 2024
• Stratified horizontal convection

  Daisuke Noto, Hugo Ulloa, Takatoshi Yanagisawa, Yuji Tasaka

  The Journal of Fluid Mechanics 970 A21  2023/08 [Refereed][Not invited]
  
• Study on Large Particle Slurry Transport in Inclined Pipes With Pulsating Flow for Subsea Mining

  Sotaro Masanobu, Satoru Takano, Marcio Yamamoto, Yuichi Murai, Yuji Tasaka, Hyun Jin Park

  Volume 4: Ocean Space Utilization 2023/06/11 

  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.
• Structural variety of developing and equilibrium horizontal convection confined in a rectangular vessel resulting from different heating plate arrangements

  T. Terada, D. Noto, Y. Tasaka, T. Miyagoshi, T. Yanagisawa

  Journal of Visualization 26 1055 - 1066 1343-8875 2023/05/08 [Refereed][Not invited]
  
• Low-cost 3D color particle tracking velocimetry: Application to thermal turbulence in water

  Daisuke Noto, Yuji Tasaka, Yuichi Murai

  Experiments in Fluids 64 92  2023/04 [Not refereed][Invited]
  
• Ultrasound measurement of large bubbles rising in angled slug pipe flows

  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]
  
• Downstream persistence of frictional drag reduction with repetitive bubble injection

  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]
  
• Optical spinning rheometry test on viscosity curves of less viscous fluids at low shear rate range

  Daisuke Noto, Kohei Ohie, Taiki Yoshida, Yuji Tasaka

  Experiments in Fluids 64 (1) 0723-4864 2023/01 [Refereed][Not invited]
  
• Behaviors of sliding bubbles in an inclinable turbulent channel flow investigated by optoacoustic measurement

  Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Yuichi Murai

  International Journal of Multiphase Flow 158 104258 - 104258 0301-9322 2023/01 [Refereed][Not invited]
  
• Flow Prediction of Complex Fluids in a Circular Pipe by Utilizing a Velocity-Profiling-Assisted Rheometer

  Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Yuichi Murai

  Industrial & Engineering Chemistry Research 61 (49) 18157 - 18164 0888-5885 2022/12/14 [Refereed][Not invited]
   

  Flow prediction of complex fluids in a circular pipe was conducted using a velocity-profiling-assisted rheometer. As application examples, shear-rate-dependent stress and viscosity of carboxymethyl cellulose and polyacrylamide aqueous solutions and rice porridge were evaluated. Carboxymethyl cellulose is a well-known thickener for foods and cosmetics; the latter two examples represent complex fluids that are outside the scope of application of a standard torque-type rheometer because the PAM solution causes shear-localization problems and the porridge includes O(1 mm) size dispersions. The obtained flow curve in shear rate range of O(10-1-101 s-1) was used to predict laminar flow in a pipe under a steady pressure gradient, which is an industrially applicable target. The predicted velocity profiles were in good agreement with experimental results measured in a pilot pipeline, where the maximum relative error of flow rate was less than 10% for all test fluids. This suggests that the application of the rheological evaluation to flow prediction has high industrial practicality to complex fluids which are out of application of the standard rheometer.
• Measurement of Multiphase Flow in an Air-lift Pipe using Ultrasound

  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 [Not refereed][Invited]
  
• Rheological characterization and flow reconstruction of polyvinylpyrrolidone aqueous solutions by means of velocity profiling-based rheometry

  Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Masako Sugihara-Seki, Yuichi Murai

  Experiments in Fluids 63 (8) 135  0723-4864 2022/08 [Refereed][Not invited]
   

  A method for reconstructing velocity fields of non-Newtonian fluids is proposed, which ensures consistency with experimentally evaluated rheological properties. A polyvinylpyrrolidone (PVP) aqueous solution for the test fluid is generally assumed as Newtonian, while it is viscoelastic in limited conditions of unsteady shear flows. Comprehensive evaluation for figuring out the dependence of viscoelasticity on applied shear deformation and its timescale was conducted by rheology mapping [Ohie et al., "Effective rheology mapping for characterizing polymer solutions utilizing ultrasonic spinning rheometry", Exp. Fluids, 63, 2 (2022)], which is based on a velocity profiling-based rheometry. It revealed the conditions of shear rate and oscillation frequency where the viscoelasticity emerges. A newly proposed convergence calculation method was adapted to this PVP solution as a demonstration for reconstructing velocity fields from the experimentally obtained data set. The proposed calculation scheme is designed not to need a separate rheological model for each complex fluid. The predicted oscillatory shear flows between double concentric cylinders were clearly different with and without the non-Newtonian characteristic. The predicted velocity profiles considering the non-Newtonian characteristic were in good agreement with verification experimental results. This indicates validity of the proposed convergence calculation method combined with the experimentally evaluated rheological properties.
• Gas volume estimation in a vertical pipe flow considering the bubble size obtained from an ultrasonic velocity vector profiler

  H.J.Park, D. Yoon, S. Akasaka, Y. Tasaka, Y. Murai

  Experiments in Fluids 63 (8) 130  0723-4864 2022/08 [Refereed]
  
• Ultrasound Doppler measurement of air-lift two-phase and particulate three-phase pipe flows

  Yuichi Murai, Takumi Hayashi, Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Satoru Takano, Sotaro Masanobu

  Experiments in Fluids 63 (8) 126  0723-4864 2022/08 [Refereed][Not invited]
   

  Air-lift two-phase and particulate three-phase flow in a vertical pipe has been measured by the ultrasound Doppler method with the aim of revealing the local transient dynamics of the multiphase fluid to explain the air-lift performance. Changing the gas flow rate and mass loading of solid particles in the liquid phase, we measured the void fraction and liquid flow rate in the slug-flow regime at 55 Hz sampling rate. The echo amplitude profile was analyzed with several space-time filtering algorithms to detect dispersed bubbles and large pipe-occupying bubbles. The Doppler-shift profiles were processed to measure the instantaneous liquid flow rate, which is correlated with the void fraction. From the synchronized measurements, we found that mixing the liquid phase with solid particles reduced the mean axial length of the bubbles and the correlation between the liquid flow rate and the void fraction was reduced because the long slug was destabilized by the particles. Graphical abstract: [Figure not available: see fulltext.]
• In Situ Measurement of Instantaneous Viscosity Curve of Fluids in a Reserve Tank

  Taiki Yoshida, Kohei Ohie, Yuji Tasaka

  Industrial & Engineering Chemistry Research 61 (31) 11579 - 11588 0888-5885 2022/07/30 [Refereed][Not invited]
   

  A novel method enabling in situ measurement in a reserve tank for evaluating an instantaneous viscosity curve is presented. This aims to satisfy the practical demand of industrial production process for monitoring real-time rheological properties without taking samples. With applicable ranges of shear rate and viscosity, O(10(-1)-10(2) s(-1)) and O(10(-2)-10(0) Pamiddots), it enables evaluation of fluid properties having shear strain rate dependence, based on ultrasonic spinning rheometry. Since this method evaluates the characteristic of shear thinning viscosity while changing the fluid temperature in a reserve tank, some useful examples are expected as further applications for measuring viscosity during chemical reaction processes, such as gelation, hydrolysis, and polymerization. Efficacy of the method evaluating rheological properties is validated by numerical and experimental results.
• Lift coefficient of bubble sliding inside turbulent boundary layers in an inclinable channel flow

  Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Yuichi Murai

  Physics of Fluids 34 (5) 053301 - 053301 1070-6631 2022/05 [Refereed][Not invited]
   

  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.
• Frictional drag reduction caused by bubble injection in a turbulent boundary layer beneath a 36-m-long flat-bottom model ship

  Taiji Tanaka, Yoshihiko Oishi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Chiharu Kawakita

  Ocean Engineering 252 111224 - 111224 0029-8018 2022/05 [Refereed][Not invited]
   

  The reduction of frictional drag caused by bubble injection was experimentally investigated in a turbulent boundary layer beneath a 36-m-long flat-bottom model ship. For this model ship towed at 8 m/s, the drag reduction increased exponentially (with a power index of 1.2) with the air flow rate, and the drag-reduction ratio reached 28% at the maximum air flow rate. The local wall shear stress measured at 23 locations on the flat-bottom surface revealed a reduction in the local friction coefficient of 50% immediately downstream of the bubble injector and 20% at the stern. This downstream decay proceeded nonlinearly, inferring that the spatial transition of local drag-reduction characteristics depends on the status of bubble dispersion. We established a formula characterizing the streamwise decay from measurements of the transition of drag-reduction characteristics along the 36 m length of the model. This formula can be used to evaluate the downstream persistence of bubbly drag reduction and estimate the full-scale performance of air lubrication technology.
• A method for evaluating time‐resolved rheological functionalities of fluid foods

  Kohei Ohie, Haruko Chiba, Satomi Kumagai, Taiki Yoshida, Yuji Tasaka

  Journal of Texture Studies 1 - 9 0022-4901 2022/04/24 [Refereed]
   

  We have developed an effective method for evaluating time-resolved rheological functionalities of swallowed foods using ultrasonic spinning rheometry (USR). USR can obtain variations over time in the rheological properties of fluids despite the fluids being in heterogeneous and nonequilibrium conditions. In addition, USR can evaluate time variations of shear-thinning property changing in a few seconds. Demonstrations were conducted with typical thickener solutions: starch, guar gum, and xanthan gum-based solutions, with alpha-amylase as a digestive enzyme. The flow curve of the starch-based solutions lowered with time, and a few minutes after addition of the amylase, the viscosity dropped to one-hundredth of the original value. In contrast, the guar gum- and xanthan gum-based solutions maintained the original viscosities as generally known. Applying the power law fitting to series of these flow curves, the time variation of the shear-thinning property is quantitatively characterized by the plots on typical K-n space, where K and n are parameters in the model, consistency index and power law exponent. The qualitative characteristics of the thickeners are successfully quantified in the K-n space, and this will be a practical tool for evaluating the time-resolved rheological properties of swallowed foods.
• Drag coefficient of bubbles sliding beneath a towed model ship with variable tilt angles

  Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Yuichi Murai

  International Journal of Multiphase Flow 149 103995 - 103995 0301-9322 2022/04 [Refereed][Not invited]
  
• Overview of Ultrasonic Spinning Rheometry: Application to Complex Fluids

  Taiki Yoshida, Yuji Tasaka, Kohei Ohie, Yuichi Murai

  Nihon Reoroji Gakkaishi 50 (1) 3 - 7 0387-1533 2022/02/15 [Not refereed][Invited]
   

  A novel rheometry termed ultrasonic spinning rheometry (USR) is overviewed in this paper. This methodology utilizes ultrasonic velocity profiling as a representative velocimetry for various complex fluids including multi-phase state. The USR determines optimal properties from cost function which is calculated from both equation of motion and constitutive equation of test fluids by substituting the measured velocity profiles. Various examples are explained to indicate the applicability and efficacy of USR for measuring complex fluids; silicon oil, polymer solution, clay dispersion, water-oil two-phase fluid, and more. Through these results, we discussed future prospects of USR developments regarding its applicability and efficacy.
• Effective rheology mapping for characterizing polymer solutions utilizing ultrasonic spinning rheometry

  Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Yuichi Murai

  EXPERIMENTS IN FLUIDS 63 (2) 0723-4864 2022/02 [Refereed][Not invited]
   

  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].
• Time-dependent viscoelastic characteristics of montmorillonite dispersion examined by ultrasonic spinning rheometry

  Taiki Yoshida, Yuji Tasaka, Peter Fischer, Yuichi Murai

  Applied Clay Science 217 106395 - 106395 0169-1317 2022/02 [Refereed][Not invited]
   

  Time-dependent viscoelastic characteristics of montmorillonite (Mt) dispersion are examined by means of ultrasonic spinning rheometry (USR). In this study, multiple timescale rheology of Mt dispersion under oscillatory shear flows is elucidated by linear viscoelastic analysis of USR. As a result, Mt dispersion with dilute NaCl concentration shows different timescales with respect to applied oscillatory frequency and shear rate. By experimental approaches, the relation between NaCl concentration and thixotropic characteristic is examined. Through experimental approaches, the rheological properties of Mt dispersion are classified into parameters with three timescales: The relaxation time of anisotropy of the Mt particles O(10(-1) s), the relaxation time depending on the applied oscillation frequency O(10(-2) s) to O(10(0) s), and time for structure recovery O(10(4)( )s). As novel experimental methodology for evaluating viscoelasticity of Mt dispersion showing thixotropy, USR is informative for understanding its complex rheological characteristics under unsteady shear conditions.
• Evaluation of time-dependent rheological property in the coagulation of skimmed milk by ultrasonic velocity profiler

  Akihide TAKANO, Kohei OHIE, Yasufumi HORIMOTO, Yuji TASAKA, Yuichi MURAI

  Transactions of the JSME (in Japanese) 88 (911) 22 - 00115 2022
• Spatial development of single void pulse in a horizontal turbulent bubbly channel flow investigated by a time-resolved two-laser measurement

  H.J. Park, Y. Tasaka, Y. Murai

  International Journal of Multiphase Flow 2022/01 [Refereed]
  
• Frictional drag reduction by bubble injection in turbulent boundary layers: Experiment with long model ship and full-scale estimation

  Taiji TANAKA, Yoshihiko OISHI, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI, Chiharu KAWAKITA

  Transactions of the JSME (in Japanese) 88 (907) 2187-9761 2022 [Refereed][Not invited]
  
• Repetitive bubble injection promoting frictional drag reduction in high-speed horizontal turbulent channel flows

  Taiji Tanaka, Yoshihiko Oishi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Chiharu Kawakita

  Ocean Engineering 239 109909 - 109909 0029-8018 2021/11 [Refereed][Not invited]
   

  Air lubrication adopting repetitive bubble injection was examined in a facility of high-speed turbulent channel flow. The bulk water velocity in the channel was controlled from 5.0 to 7.0 m/s, resulting in a channel Reynolds number Rem > 105 and friction Reynolds number Reτ > 103. Bubbles were injected with gas flow rates periodically fluctuating at frequencies of 1.0–6.0 Hz in the upstream section of the channel. In the downstream of the channel, a periodic pattern of bubble distributions and a periodic fluctuation of wall shear stress were observed at a frequency coinciding to the frequency of bubble injection. Measurements of the wall shear stress show that the ratio of the time-averaged drag reduction was improved by the repetitive bubble injection relative to the conventional method of continuous bubble injection. The largest ratio was obtained at a frequency of 2.0 Hz. Under this condition, the ratio of the drag reduction per unit volume of injected gas was almost twice that for continuous bubble injection, demonstrating the superiority of repetitive bubble injection in terms of the efficiency of drag reduction.
• Ultrasonic Doppler Technique for Application to Multiphase Flows: A Review

  Chao Tan, Yuichi Murai, Weiling Liu, Yuji Tasaka, Feng Dong, Yasushi Takeda

  International Journal of Multiphase Flow 144 103811 - 103811 0301-9322 2021/11 [Refereed][Not invited]
  
• Color-coded smoke PIV for wind tunnel experiments improved by eliminating optical and digital color contamination

  Yuichi Murai, Takeaki Yumoto, Hyun Jin Park, Yuji Tasaka

  Experiments in Fluids 62 2021/10 [Refereed][Not invited]
  
• Bifurcation analysis of bubble-induced convection in a horizontal liquid layer: role of forces on bubbles

  Kotaro Nakamura, Harunori N. Yoshikawa, Yuji Tasaka, Yuichi Murai

  Journal of Fluid Mechanics 923 0022-1120 2021/09/25 [Refereed][Not invited]
   
• Developing horizontal convection against stable temperature stratification in a rectangular container

  Daisuke Noto, Tomomi Terada, Takatoshi Yanagisawa, Takehiro Miyagoshi, Yuji Tasaka

  Physical Review Fluids 6 (8) 083501  2021/08/25 [Refereed][Not invited]
  
• Nonintrusive In-Line Rheometry Using Ultrasonic Velocity Profiling

  Yuji Tasaka, Taiki Yoshida, Yuichi Murai

  Industrial & Engineering Chemistry Research 0888-5885 2021/07/14 [Refereed][Not invited]
  
• In situ color-to-depth calibration: toward practical three-dimensional color particle tracking velocimetry

  D. Noto, Y. Tasaka, Y. Murai

  Experiments in Fluids 62 (6) 0723-4864 2021/06 [Refereed][Not invited]
  
• Bubble fragmentation dynamics in a subsonic Venturi tube for the design of a compact microbubble generator

  Yuichi Murai, Yuji Tasaka, Yoshihiko Oishi, Patricia Ern

  International Journal of Multiphase Flow 139 103645 - 103645 0301-9322 2021/06 [Refereed][Not invited]
  
• Dual-plane ensemble correlation for pixelwise 2D-3C velocity field measurements using a single camera

  D. Noto, Y. Tasaka

  Experiments in Fluids 62 (5) 0723-4864 2021/05 [Refereed][Not invited]
  
• Coupling structures of two-layer natural convection in a cylindrical vessel investigated by simultaneous two-layer visualization

  Daisuke Noto, Yuji Tasaka, Yuichi Murai

  Experimental Thermal and Fluid Science 127 110394 - 110394 0894-1777 2021/04 [Refereed][Not invited]
  
• Development of multi-cycle rainbow particle tracking velocimetry improved by particle defocusing technique and an example of its application on twisted Savonius turbine

  Hyun Jin Park, Shunta Yamagishi, Susumu Osuka, Yuji Tasaka, Yuichi Murai

  Experiments in Fluids 62 (4) 71  0723-4864 2021/04 [Refereed][Not invited]
  
• Stepwise transitions in spin-up of rotating Rayleigh–Bénard convection

  D. Noto, Y. Tasaka, T. Yanagisawa, T. Miyagoshi

  Journal of Fluid Mechanics 911 0022-1120 2021/03/25 [Refereed][Not invited]
   
• Two-dimensional oscillation of convection roll in a finite liquid metal layer under a horizontal magnetic field

  Y. Tasaka, T. Yanagisawa, K. Fujita, T. Miyagoshi, A. Sakuraba

  Journal of Fluid Mechanics 911 A19  0022-1120 2021/03/25 [Refereed][Not invited]
   
• PIV-based estimation of viscosity and pressure fields for a steady pseudoplastic flow

  Neetu Tiwari, Yuji Tasaka, Yuichi Murai

  Flow Measurement and Instrumentation 77 0955-5986 2021/03/01 

  Targeting a pseudoplastic fluid, we propose a method to simultaneously estimate viscosity and pressure fields from the velocity field data of particle image velocimetry (PIV). As a two-dimensional case study, we chose a steady two-dimensional wake structure behind a circular cylinder where local viscosity and pressure are dynamically coupled. The method involves PIV, momentum conservation equation of non-Newtonian fluids and rheological constitutive equations. The CMC (Carboxy Methyl Cellulose) aqueous solution of weight concentration of 0.1% is used as a test case of pseudoplastic fluid. Viscosity distribution is obtained through power law model and Carreau-Yasuda model as the constitutive equation. Pressure distribution is then calculated by substituting the viscosity into the momentum conservation equation. Applied results show pressure-lowering at the vortex cores and viscosity-lowering at their perimeters, stabilizing vortex attachment to the cylinder in the pseudoplastic fluid. We also analyze error propagation characteristics to conclude the feasibility of the present method and highlight the difference in error propagation characteristics during pressure estimation between Newtonian and pseudoplastic fluid flows.
• Measurement of the inner structure of turbidity currents by ultrasound velocity profiling

  Jumpei Hitomi, Shun Nomura, Yuichi Murai, Giovanni De Cesare, Yuji Tasaka, Yasushi Takeda, Hyun Jin Park, Hide Sakaguchi

  International Journal of Multiphase Flow 136 103540 - 103540 0301-9322 2021/03 [Refereed][Not invited]
   

  © 2020 The inner velocity structure and particle concentration profile of opaque turbidity currents were measured simultaneously by ultrasound velocity profilers. Currents consisting of a quartz particle suspension were generated by using the lock-exchange method in a flume to experimentally reproduce the quasi-steady state of a turbidity current. A pair of ultrasound transducers captured the horizontal and vertical velocities from Doppler frequencies, and the particle concentration profile was extracted from the echo amplitude. The data obtained were analyzed in terms of momentum conservation according to the two-fluid model. We found that: i) the viscous and Reynolds shear stresses balance in the top half of the current; and ii) the lower border of the stress balancing appears around the depth of the maximum vertical density gradient. These findings indicate that the reduction of flow resistance inside the body region of the turbidity current is maintained downstream, which enables the current to transport particles over a long distance.
• Ultrasonic Spinning Rheometry Test of Food Rheology for better Swallowing

  田坂裕司, 芳田泰基, 大家広平, 熊谷聡美

  月刊ファインケミカル 50 (2) 41 - 47 0913-6150 2021/02 [Not refereed][Invited]
  
• Wall shear stress modified by bubbles in a horizontal channel flow of silicone oil in the transition region

  Yosihiko Oishi, Yuichi Murai, Yuji Tasaka

  International Journal of Heat and Fluid Flow 86 0142-727X 2020/12 [Refereed]
  
• Linear stability analysis of bubble-induced convection in a horizontal liquid layer

  Kotaro Nakamura, Harunori N. Yoshikawa, Yuji Tasaka, Yuichi Murai

  Physical Review E 102 (5) 053102  2470-0045 2020/11/02 [Refereed][Not invited]
   

  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.
• Evaluation on time variation of effective viscosity by ultrasonic spinning rheometry (Application to separating oil-water mixture)

  Kohei OHIE, Taiki YOSHIDA, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI

  Transactions of the JSME (in Japanese) 86 (890) 2187-9761 2020/11 [Refereed][Not invited]
  
• Mechanism and performance of a hydrofoil bubble generator utilized for bubbly drag reduction ships

  Yuichi Murai, Haruki Sakamaki, Ichiro Kumagai, Hyun Jin Park, Yuji Tasaka

  Ocean Engineering 216 108085 - 108085 0029-8018 2020/11 [Refereed][Not invited]
  
• Applicability evaluation of the stress-optic law in Newtonian fluids toward stress field measurements

  Daisuke Noto, Yuji Tasaka, Jumpei Hitomi, Yuichi Murai

  Physical Review Research 2 (4) 2020/10/21 [Refereed][Not invited]
  
• Spontaneous and artificial void wave propagation beneath a flat-bottom model ship

  Taiji Tanaka, Hyun Jin Park, Yuji Tasaka, Yuichi Murai

  Ocean Engineering 214 107850 - 107850 0029-8018 2020/10 [Refereed][Not invited]
  
• Anti-wind characteristics and fall-down resistance mechanism of road cones with opened holes

  Toshiki ASHIDA, Yuichi MURAI, Hyun Jin PARK, Yuji TASAKA, Shigeyuki NAGAI

  Transactions of the JSME (in Japanese) 86 (888) 20 - 00184 2020/08 [Refereed][Not invited]
  
• Three-dimensional visualization of columnar vortices in rotating Rayleigh–Bénard convection

  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
• Simultaneous optical measurement of temperature and velocity fields in solidifying liquids

  S. Anders, D. Noto, Y. Tasaka, S. Eckert

  Experiments in Fluids 61 (4) 0723-4864 2020/04 [Refereed][Not invited]
   

  We introduce a complex image processing scheme for the simultaneous application of liquid crystal thermometry (LCT), in addition to the previously established method in Anders et al. (Exp Fluids 60(4):68, 2019. 10.1007/s00348-019-2703-8) for particle tracking velocimetry and particle image velocimetry. This scheme was developed for an experimental study on the double-diffusive convection in an aqueous ammonium chloride solution NH₄Cl(aq) during crystallization. The use of thermochromic liquid crystals (TLC) enables to visualize the flow and temperature field simultaneously. We present a color interpolation method that enhances the accuracy of the LCT by yielding RGB images only representative of the TLC’s coloration. An artificial neural network (ANN) which processes RGB triplets and spatial color dependencies transforms these images into temperature fields. The combination of the ANN system and a corresponding calibration procedure enhances the accuracy and measurable temperature range of the LCT compared to state-of-the-art procedures. By using the here established measurement scheme, quantitative global studies of the mutual influence between solidification and convection are enabled and exemplary results are presented.
• Artificial Void Wave Propagation in a Gas-Liquid Two-Phase Horizontal Turbulent Channel Flow

  Taiji TANAKA, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI

  JAPANESE JOURNAL OF MULTIPHASE FLOW 34 (1) 243 - 253 0914-2843 2020/03/17 [Refereed][Not invited]
  
• Monitoring of Void Fraction and Bubble Size in Narrow-channel Bubbly-flows using Ultrasonic Pulses with A Super Bubble-resonant Frequency

  Hyun Jin Park, Shintaro Akasaka, Yuji Tasaka, Yuichi Murai

  IEEE Sensors Journal 1 - 1 1530-437X 2020 [Refereed][Not invited]
  
• Rheometric Test for Multiphase Fluids by Means of Ultrasonic Spinning Rheometry

  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 [Not refereed][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.

• Ultrasonic spinning rheometry test on the rheology of gelled food for making better tasting dessert

  Taiki Yoshida, Yuji Tasaka, Peter Fischer

  Physics of Fluids (special topic: Food and Fluids) 31 (11) 113101  1070-6631 2019/11 [Refereed][Not invited]
   

  Rheological properties of gelled foods that may relate to the physics of the fluids in the swallowing process of complex food components are determined by ultrasonic spinning rheometry (USR) [T. Yoshida et al., "Efficacy assessments in ultrasonic spinning rheometry: Linear viscoelastic analysis on non-Newtonian fluids," J. Rheol. 63, 503-517 (2019)]. Through 'theological evaluations of thixotropic gelled food, the inaccuracies in standard rheometer data to capture the true-rheological property are discussed first with steady rotational and oscillatory tests; the inaccuracies arise from commonly existing problems that cannot be directly observed in standard rheometers (wall-slip, shear banding, shear localization, elastic instability, etc.). The results evaluated by standard rheometers would be related to the measurements being specific response, depending on the geometry of the measurement device. The USR test discussed here shows the potential to overcome these problems in the rheological evaluation of gelled foods and reflects the advantages offered by USR such as spatial, local, and oscillation cycle measurements; the results with the transient flow curve that has not previously been discussed can be usefully interpreted, and the stability of the food materials in the unsteady shear displayed is of great importance in understanding which rheology indicates the better texture. Published under license by AIP Publishing
• Bubble Clustering in a Horizontal Turbulent Channel Flow Investigated via Bubble-Tracking Velocimetry

  Yoshihiko Oishi, Yukihiro Tohge, Yuji Tasaka, Yuichi Murai

  International Journal of Multiphase Flow 120 1031104  0301-9322 2019/11 [Refereed][Not invited]
  
• Effective viscoelasticity of non-Newtonian fluids modulated by large-spherical particles aligned under unsteady shear

  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.
• 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]
  
• Color-coded visualization of microbubble clouds interacting with eddies in a spatially developing turbulent boundary layer

  Hyun Jin Park, Daichi Saito, Yuji Tasaka, Yuichi Murai

  Experimental Thermal and Fluid Science 109 109919  0894-1777 2019/09 [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.
• Rheological evaluations of complex fluids by ultrasonic velocity profiling

  Yuji Tasaka, Taiki Yoshida, Yuichi Murai

  Nagare 38 (4) 283‐290  0286-3154 2019/08/25 [Not refereed][Invited]
  
• Quantitative visualization of vortex ring structure during wall-impingement subject to background rotation

  Y.Oishi, Y.Murai, Y.Tasaka

  Journal of Visualization 22 867 - 876 1343-8875 2019/07 [Refereed][Not invited]
  
• Horizontal diffusive motion of columnar vortices in rotating Rayleigh-Bénard convection

  D. Noto, Y. Tasaka, T. Yanagisawa, Y. Murai

  Journal of Fluid Mechanics 871 401 - 426 0022-1120 2019/05 [Refereed][Not invited]
   

  In laboratory experiments, horizontal translational motion of columnar vortices formed in rotating Rayleigh–Bénard convection was investigated. Two types of measurements, vertical velocity fields and horizontal temperature fields, were conducted with water as the test fluid. Using particle image velocimetry, the vertical velocity fields determined the parameter range at which the quasi-two-dimensional columnar vortices emerged. Locally, the duration characteristics of the columns, evaluated with their vertical coherence, indicate the minimum time scale of translational motion of the vortices in the horizontal plane. Vortex tracking of the horizontal temperature fields over long observation periods (${>}10^{3}~\text{s}$) was conducted using encapsulated thermochromic liquid crystal visualization. Two cylindrical vessels with different radii showed the emergence of the centrifugal effect in $O({>}10^{2}~\text{s})$ despite the small Froude number ($Fr<0.1$). Further, in the horizontal plane the columnar vortices behaved in a random-walk-like diffusive motion. The statistically calculated mean-squared displacements indicated anomalous diffusive motion of the columns; displacement increasing with time as $t^{\unicode[STIX]{x1D6FE } }$ with $\unicode[STIX]{x1D6FE}\neq 1$. We discuss the causes of this anomaly in both the instantaneous and long-term statistical data gathered from experimental observations over different time scales. The enclosure effect from the repulsion of up-welling and down-welling vortices ensures that vortices diffuse only little, resulting in a sub-diffusive (decelerated) motion $\unicode[STIX]{x1D6FE}<1$ in $O(10^{1}~\text{s})$. With this weak centrifugal contribution, the translational motion of the columns slowly accelerates in the radial direction and thereby yields a super-diffusive (accelerated) motion $\unicode[STIX]{x1D6FE}>1$ in $O(10^{2}~\text{s})$.
• Efficacy assessments in ultrasonic spinning rheometry: Linear viscoelastic analysis on non-Newtonian fluids

  Taiki Yoshida, Yuji Tasaka, Yuichi Murai

  Journal of Rheology 63 (4) 503 - 516 0148-6055 2019/05 [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.
• Pressure field estimation from ultrasound Doppler velocity profiler for vortex-shedding flows

  Neetu Tiwari, Yuji Tasaka, Yuichi Murai

  Flow Meas. Instr. 67 23 - 32 0955-5986 2019/04 [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.
• Transition from convection rolls to large-scale cellular structures in turbulent Rayleigh-Bénard convection in a liquid metal layer

  Megumi Akashi, Takatoshi Yanagisawa, Yuji Tasaka, Tobias Vogt, Yuichi Murai, Sven Eckert

  Physical Review Fluids 4 (3) 033501  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.
• Visualization of microbubble distribution inside turbulent boundary layer along flat and curved solid surfaces

  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.
• Void waves developing in gas–liquid two-phase turbulent boundary layers beneath a flat bottom model ship

  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.
• Three-dimensional measurement of smoke density distribution by switching volumetric color illumination patterns

  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.
• Inwardly rotating spirals in a non oscillatory medium

  Harunori N. Yoshikawa, Christian Mathis, Shu Satoh, Yuji Tasaka

  Physical Review Letters 122 14502  0031-9007 2019/01 [Refereed][Not invited]
  
• Bubbly drag reduction investigated by time-resolved ultrasonic pulse echography for liquid films creeping inside a turbulent boundary layer

  Hyun Jin Park, Yuji Tasaka, Yuichi Murai

  Exp. Thermal and Fluid Sci. 103 66 - 77 0894-1777 2019/01 [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.
• Bubbly drag reduction accompanied by void wave generation inside turbulent boundary layers

  Hyun Jin Park, Yuji Tasaka, Yuichi Murai

  Experiments in Fluids 59 (11) 166  0723-4864 2018/10 [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.
• Modal switching of bubbly Taylor-Couette flow investigated by particle tracking velocimetry

  Yuichi Murai, Yuji Tasaka, Yoshihiko Oishi, Yasushi Takeda

  Experiments in Fluids 59 (11) 164  0723-4864 2018/10 [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
• 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 Clay Science 161 513 - 523 0169-1317 2018/09/01 [Refereed][Not invited]
   

  Rheological changes of gelled montmorillonite dispersions with different NaCl concentrations and alkali conditions were evaluated by ultrasonic spinning rheometry. It uses velocity-profile information that is obtained in an open-cylindrical container under periodic oscillations. The measurement was conducted with a focus on the rheological behavior at a low shear rate O(1 s−1), which is difficult to measure because of shear banding. The rheometry represents the coexistence of gel and sol conditions in dispersions as profiles of the phase lag of oscillations that are propagated from the cylinder wall. The critical shear rate at a yielding point and the onset of shear-thinning behavior was quantified, which has been regarded as only an apparent or speculated value by many previous researchers. Viscoelasticity from particle networks in the dispersion was observed, and the networks deform like a spring, without breaking the structure under low-shear-rate conditions.
• Subcritical transition to turbulence in a sudden circular pipe expansion

  Benoît Lebon, Jorge Peixinho, Shun Ishizaka, Yuji Tasaka

  Journal of Fluid Mechanics 849 340 - 354 1469-7645 2018/08/25 [Refereed][Not invited]
   

  The results of experiments on the flow through a circular sudden expansion pipe at moderate Reynolds numbers are presented. At five diameters upstream of the expansion, laminar flow was disturbed by a (constant) cross-flow jet, a suction or a (periodic in-out) synthetic jet from a hole in the wall. When the disturbance exceeded a critical value of the control parameter depending on the Reynolds number, localised turbulent patches formed downstream of the expansion at fixed axial positions. For the cross-flow jet, the onset of turbulent patches is related to the velocity ratio of the mean jet velocity to the mean pipe velocity. At low velocity ratio, turbulent patches formed intermittently. For the suction disturbance, the flow experienced a strong asymmetry of the recirculation region and required a larger velocity ratio before the turbulent patch formed. For the synthetic jet, the amplification of wavy disturbances into turbulent patches and their axial positions are controlled by the driving frequency. Overall, these results suggest the existence of different mechanisms for the development of localised turbulent patches.
• Inner structure visualization of fresh fruits utilizing ultrasonic velocity profiler

  Taiki Yoshida, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hiroki Teramura, Shigenobu Koseki

  Journal of Visualization 21 (2) 253 - 265 1875-8975 2018/04/01 [Refereed][Not invited]
   

  Abstract: 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.
• Linear viscoelastic analysis using frequency-domain algorithm on oscillating circular shear flows for bubble suspensions

  Yuji Tasaka, Taiki Yoshida, Richard Rapberger, Yuichi Murai

  Rheologica Acta 57 (3) 229 - 240 0035-4511 2018/03/01 [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.
• Vortex tracking on visualized temperature fields in a rotating Rayleigh-Bénard convection

  Daisuke Noto, Yuji Tasaka, Takatoshi Yanagisawa, Hyun Jin Park, Yuichi Murai

  Journal of Visualization 21 (6) 987 - 998 1343-8875 2018 [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.
• Transition between quasi-two-dimensional and three-dimensional Rayleigh-Bénard convection in a horizontal magnetic field

  Tobias Vogt, Wataru Ishimi, Takatoshi Yanagisawa, Yuji Tasaka, Ataru Sakuraba, Sven Eckert

  Physical Review Fluids 3 (1) 013503  2469-990X 2018/01/01 [Refereed][Not invited]
   

  Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally and numerically using a liquid metal inside a box with a square horizontal cross section and an aspect ratio of 5. Applying a sufficiently strong horizontal magnetic field converts the convective motion into a flow pattern of quasi-two-dimensional (quasi-2D) rolls arranged parallel to the magnetic field. The aim of this paper is to provide a detailed description of the flow field, which is often considered as quasi-2D. In this paper, we focus on the transition from a quasi-two-dimensional state toward a three-dimensional flow occurring with decreasing magnetic-field strength. We present systematic flow measurements that were performed by means of ultrasound Doppler velocimetry. The measured data provide insight into the dynamics of the primary convection rolls, the secondary flow induced by Ekman pumping, and they reveal the existence of small vortices that develop around the convection rolls. New flow regimes have been identified by the velocity measurements, which show a pronounced manifestation of three-dimensional flow structures as the ratio Ra/Q increases. The interaction between the primary swirling motion of the convection rolls and the secondary flow becomes increasingly strong. Significant bulging of the convection rolls causes a breakdown of the original recirculation loop driven by Ekman pumping into several smaller cells. The flow measurements are completed by direct numerical simulations. The numerical simulations have proven to be able to qualitatively reproduce the newly discovered flow regimes in the experiment.
• Rheological evaluation of complex fluids using ultrasonic spinning rheometry in an open container

  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.
• Quantitative visualization of swirl and cloud bubbles in Taylor-Couette flow

  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.
• Influence of microbubbles on turbulent puffs in pipe flows

  中村幸太郎, 田坂裕司, 村井祐一

  混相流, Vol. 31 2017/04 [Refereed][Not invited]
  
• Surface switching statistics of rotating fluid: Disk-rim gap effects

  Yuji Tasaka, Makoto Iima

  PHYSICAL REVIEW E 95 (4) 043113  2470-0045 2017/04 [Refereed][Not invited]
   

  We examined the influence of internal noise on the irregular switching of the shape of the free surface of fluids in an open cylindrical vessel driven by a bottom disk rotating at constant speed [Suzuki, Iima, and Hayase, Phys. Fluids 18, 101701 (2006)]. A slight increase in the disk-rim gap (less than 3% of the disk radius) was established experimentally to cause significant changes in this system, specifically, frequent appearance of the surface descending event connecting a nonaxisymmetric shape in strong mixing flow (turbulent flow) and an axisymmetric shape in laminar flow, as well as a shift in critical Reynolds number that define the characteristic states. The physical mechanism underlying the change is analyzed in terms of flow characteristics in the disk-rim gap, which acts as a noise source, and a mathematical model established from measurements of the surface height fluctuations with noise term.
• Ultrasound Flow-Monitoring and Flow-Metering of Air-Oil-Water Three-Layer Pipe Flows

  Junpei Hitomi, Yuichi Murai, Hyun Jin Park, Yuji Tasaka

  IEEE ACCESS 5 (1) 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.
• Oil mist transport process in a long pipeline on turbulent flow transition region

  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.
• Void waves propagating in the bubbly two-phase turbulent boundary layer beneath a flat-bottom model ship during drag reduction

  Hyun Jin Park, Yoshihiko Oishi, Yuji Tasaka, Yuichi Murai

  EXPERIMENTS IN FLUIDS 57 (12) 1 - 18 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.
• Extraction of 3D vortex structures from a turbulent puff in a pipe using two-color illumination and flakes

  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. .
• Regular flow reversals in Rayleigh-Benard convection in a horizontal magnetic field

  Yuji Tasaka, Kazuto Igaki, Takatoshi Yanagisawa, Tobias Vogt, Till Zuerner, Sven Eckert

  PHYSICAL REVIEW E 93 (4) 043109  2470-0045 2016/04 [Refereed][Not invited]
   

  Magnetohydrodynamic Rayleigh-Benard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2 x 10(3) < Q < 10(4) and 5 x 10(3) < Ra < 3 x 10(5), thus extending the regime diagram provided by Yanagisawa et al. [T. Yanagisawa et al., Phys. Rev. E 88, 063020 (2013)]. Three regimes were identified, of which the regime of regular flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra/Q = 10, where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.
• Viscoelastic responses of flow driven by a permeable disk investigated by ultrasound velocity profiling

  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.
• Dynamics of flow structures and surface shapes in the surface switching of rotating fluid

  M. Iima, Y. Tasaka

  JOURNAL OF FLUID MECHANICS 789 402 - 424 0022-1120 2016/02 [Refereed][Not invited]
   

  We present a study of the dynamics of the free-surface shape of a flow in a cylinder driven by a rotating bottom. Near the critical Reynolds number of the laminar-turbulent transition of the boundary layer, the free surface exhibits irregular surface switching between axisymmetric and non-axisymmetric shapes, and the switching often occurs with a significant change in the free-surface height. Although such surface deformation is known to be caused by the flow structures, the detailed flow structures of a rotating fluid with a large surface deformation have yet to be analysed. We thus investigate the velocity distribution and surface shape dynamics and show that the flow field during the loss of its axisymmetry is similar to that predicted by the theory of Tophoj et al. (Phys. Rev. Lett., vol. 110, 2013, 194502). The slight difference observed by quantitative comparison is caused by the fact that the basic flow of our study contains a weak rigid-body rotation in addition to the potential flow assumed by the theory. Furthermore, the observed non-axisymmetric surface shape, which has an elliptic horizontal cross-section, is generally associated with a quadrupole vortex structure. It is also found that the relative position between the free surface and the flow structure changes before and after the detachment of the free surface from the bottom. The change just after the detachment is drastic and occurs via a transient dipole-like vortex structure.
• Rapid rheological characterization of a viscoelastic fluid based on spatiotemporal flow velocimetry

  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.
• Ultrasonic pulse echography for bubbles traveling in the proximity of a wall

  Hyun Jin Park, Yuji Tasaka, Yuichi Murai

  MEASUREMENT SCIENCE AND TECHNOLOGY 26 (12) 125301  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.
• Drag reduction promoted by repetitive bubble injection in turbulent channel flows

  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.
• Ultrasonic velocity profiling rheometry based on a widened circular Couette flow

  Takahisa Shiratori, Yuji Tasaka, Yoshihiko Oishi, Yuichi Murai

  MEASUREMENT SCIENCE AND TECHNOLOGY 26 (8) 085302  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.
• Estimating the effective viscosity of bubble suspensions in oscillatory shear flows by means of ultrasonic spinning rheometry

  Y. Tasaka, T. Kimura, Y. Murai

  EXPERIMENTS IN FLUIDS 56 (1) DOI 10.1007/s00348-014-1867-5  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.
• Vortical structures swept by a bubble swarm in turbulent boundary layers

  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.
• Flow control using microbubbles and some approaches for ship drag reduction

  Y. Tasaka, T. Watamura, H.J. Park, Y. Murai, Y. Oishi

  Chemical engineering of Japan 化学工学会 78 (9) 593 - 596 0375-9253 2014/09 [Not refereed][Invited]
  
• 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]
  
• 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

  日本混相流学会論文集 28 (1) 81 - 89 2014 [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

  日本混相流学会論文集 28 (1) 71 - 80 2014 [Refereed][Not invited]
  
• Convection patterns in a liquid metal under an imposed horizontal magnetic field

  Takatoshi Yanagisawa, Yozo Hamano, Takehiro Miyagoshi, Yasuko Yamagishi, Yuji Tasaka, Yasushi Takeda

  PHYSICAL REVIEW E 88 (6) 063020  1539-3755 2013/12 [Refereed][Not invited]
   

  We performed laboratory experiments of Rayleigh-Benard convection with liquid gallium under various intensities of a uniform imposed horizontal magnetic field. An ultrasonic velocity profiling method was used to visualize the spatiotemporal structure of the flows with simultaneous monitoring of the temperature fluctuations in the liquid gallium layer. The explored Rayleigh numbers Ra range from the critical value for onset of convection to 105; the Chandrasekhar number Q covers values up to 1100. A regime diagram of the convection patterns was established in relation to the Ra and Q values for a square vessel with aspect ratio 5. We identified five flow regimes: (I) a fluctuating large-scale pattern without rolls, (II) weakly constrained rolls with fluctuations, (III) a continuous oscillation of rolls, (IV) repeated roll number transitions with random reversals of the flow direction, and (V) steady two-dimensional (2D) rolls. These flow regimes are classified by the Ra/Q values, the ratio of the buoyancy to the Lorentz force. Power spectra from the temperature time series indicate that regimes I and II have the features of developed turbulence, while the other regimes do not. The region of steady 2D rolls (Busse balloon) extends to high Ra values in the present setting by a horizontal magnetic field and regime V is located inside the Busse balloon. Concerning the instabilities of the steady 2D rolls, regime III is the traveling wave convection developed from the oscillatory instability. Regime IV can be regarded as a state of phase turbulence, which is induced by intermittent occurrences of the skewed-varicose instability.
• Development of ultrasonic visualizer for capturing the characteristics of viscoelastic fluids

  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.
• 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]
  
• Intensified and attenuated waves in a microbubble Taylor-Couette flow

  T. Watamura, Y. Tasaka, Y. Murai

  PHYSICS OF FLUIDS 25 (5) 054107  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.
• LCD-projector-based 3D color PTV

  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]
  
• 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]
  
• Spatiotemporal structure of density destratification by a bubble plume

  Hidekazu Kitaura, Yuichi Murai, Yuji Tasaka, Ichiro Kumagai, Seiji Kino

  Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 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. © 2013 The Japan Society of Mechanical Engineers.
• Modification of Effective Viscosity on Bubbly Flows due to Transient Bubble Deformations

  SAKURAI KOSUKE, TASAKA YUJI, MURAI YUICHI

  日本機械学会論文集 B編(Web) 79 (797) WEB ONLY 1-11  1884-8346 2013 [Not refereed][Not invited]
  
• Quantitative visualization of microbubble stream in Taylor vortices

  Tomoaki WATAMURA, Yuji TASAKA, Yuichi MURAI

  Theoretical and Applied Mechanics Japan 61 123 - 131 2013 [Refereed][Not invited]
  
• Errata: Modification of Effective Viscosity on Bubbly Flows due to Transient Bubble Deformations [TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B, Vol. 79 (2013), No. 797, pp.1-11]

  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．
• Visualization of Turbulent Gas-liquid Two-phase Flows in a Horizontal Channel

  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]
  
• Flow-induced Oscillations of an Air-water Interface and Intermittent Bubble Entrainment by Vortices behind a Moving Cylinder

  KUMAGAI Ichiro, OYABU Koji, TASAKA Yuji, MURAI Yuichi

  混相流 = Japanese journal of multiphase flow 日本混相流学会 25 (5) 399 - 406 0914-2843 2012/03 [Not refereed][Not invited]
  
• Flow behavior around a hydrofoil close to a free surface

  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]
  
• Optimization of a Hydrofoil Air Pump for Reduction in CO2 Emissions from Ships

  KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji

  TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B 一般社団法人 日本機械学会 78 (787) 500 - 503 1884-8346 2012 [Not refereed][Not invited]
   

  We have invented a new power-saving device for ship drag reduction using microbubbles in order to reduce CO2 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 CO2 ton/year if international shipping uses this new device, with 10% net-power reduction. We present the principal and optimizat...
• Optimization of a hydrofoil air pump for reduction in CO 2 emissions from ships

  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.
• Spontaneous flow reversals in Rayleigh-Benard convection of a liquid metal

  Takatoshi Yanagisawa, Yasuko Yamagishi, Yozo Hamano, Yuji Tasaka, Yasushi Takeda

  PHYSICAL REVIEW E 83 (3) 036307  1539-3755 2011/03 [Refereed][Not invited]
   

  We report a finding of spontaneous flow reversals of roll-like patterns in liquid gallium Rayleigh-Benard convection. The vessel has a square geometry with an aspect ratio of 5, and a horizontal magnetic field is applied to align the rolls. The flow patterns were visualized by ultrasonic velocity measurements, and the processes of the reversal were clearly observed. The basic flow pattern observed in the vessel is a four-roll structure with its axis parallel to the magnetic field. Emergence of a new circulation at a corner of the vessel causes flow reversal with reorganization of the whole pattern. The flow keeps relatively steady four-roll structure for most of the duration, while the reversal of it is over in a short time. The reversals of the flow occur randomly with the interval time between reversals being much longer than the circulation time.
• Interactive flow field around two Savonius turbines

  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.
• Quantitative Visualization of Buoyant Rise Process in a Swarm of Microbubble Plumes

  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...
• Bubble Generation by a Cylinder Moving Beneath a Free Surface

  KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji, NAKAMURA Naoya

  JFST The Japan Society of Mechanical Engineers 6 (6) 851 - 859 1880-5558 2011 

  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.
• Analysis of Global Flow Structure

  Makoto Iima, Yuji Tasaka, Takeshi Watanabe

  GAKUTO International Series, Mathematical Sciences and Applications 34 25 - 38 2011 [Refereed][Not invited]
  
• Detailed investigation of thermal convection in a liquid metal under a horizontal magnetic field: Suppression of oscillatory flow observed by velocity profiles

  Takatoshi Yanagisawa, Yasuko Yamagishi, Yozo Hamano, Yuji Tasaka, Kanako Yano, Jumpei Takahashi, Yasushi Takeda

  PHYSICAL REVIEW E 82 (5) 056306  1539-3755 2010/11 [Refereed][Not invited]
   

  Thermal convection experiments in a liquid gallium layer were carried out with various intensities of uniform horizontal magnetic fields. The gallium layer was in a rectangular vessel with a 4:1:1 length ratio (1 is the height), where the magnetic field is applied in the direction normal to the longest vertical wall. An ultrasonic velocity profiling method was used to visualize the spatiotemporal variations in the flow pattern, and the temperature fluctuations in the gallium layer were also monitored. The observed flow pattern without a magnetic field shows oscillating rolls with axes normal to the longest vertical wall of the vessel. The oscillatory motion of the flow pattern was suppressed when increasing the applied magnetic field. The flow behavior was characterized by the fluctuation amplitude of the oscillation and the frequency in the range of Rayleigh numbers from 9.3 x 10(3) to 3.5 x 10(5) and Chandrasekhar numbers 0-1900. The effect of the horizontal magnetic field on the flow pattern may be summarized into three regimes with increases in the magnetic intensity: (1) no effect of the magnetic field, (2) a decrease in the oscillation of the roll structure, and (3) a steady two-dimensional roll structure with no oscillation. These regimes may be explained as a result of an increase in the dominance of Lorentz forces over inertial forces. The power spectrum from the temperature time series showed the presence of a convective-inertial subrange above Rayleigh numbers of 7 x 10(4), which suggests that turbulence has developed, and such a subrange was commonly observed above this Rayleigh number even with applied magnetic fields when the rolls oscillate.
• Folded Edge of Turbulence in a Pipe

  Y. Tasaka, T. M. Schneider, T. Mullin

  PHYSICAL REVIEW LETTERS 105 (17) 174502  0031-9007 2010/10 [Refereed][Not invited]
   

  The results of an experimental investigation into the threshold boundary between laminar and disordered pipe flow are presented. Complex features have been uncovered using a highly refined experimental approach where an intermediate periodic state forms an integral part of the transition sequence. In accord with the suggestions produced by a numerical investigation, the boundary is found to be folded with a complicated structure. This raises important questions about accepted definitions of threshold amplitudes in this long-standing problem.
• Ultrasonic detection of moving interfaces in gas-liquid two-phase flow

  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.
• Structure of large-scale flows and their oscillation in the thermal convection of liquid gallium

  Takatoshi Yanagisawa, Yasuko Yamagishi, Yozo Hamano, Yuji Tasaka, Masataka Yoshida, Kanako Yano, Yasushi Takeda

  PHYSICAL REVIEW E 82 (1) 016320  1539-3755 2010/07 [Refereed][Not invited]
   

  This investigation observed large-scale flows in liquid gallium and the oscillation with Rayleigh-Benard convection. An ultrasonic velocity profiling method was used to visualize the spatiotemporal flow pattern of the liquid gallium in a horizontally long rectangular vessel. Measuring the horizontal component of the flow velocity at several lines, an organized roll-like structure with four cells was observed in the 1 x 10(4)-2 x 10(5) range of Rayleigh numbers, and the rolls show clear oscillatory behavior. The long-term fluctuations in temperature observed in point measurements correspond to the oscillations of the organized roll structure. This flow structure can be interpreted as the continuous development of the oscillatory instability of two-dimensional roll convection that is theoretically investigated around the critical Rayleigh number. Both the velocity of the large-scale flows and the frequency of the oscillation increase proportional to the square root of the Rayleigh number. This indicates that the oscillation is closely related to the circulation of large-scale flow.
• Experimental study of cell pattern formation induced by internal heat sources in a horizontal fluid layer

  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.
• Visualization of transient interfacial waves induced by spin-up of two immiscible fluid layers

  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.
• A time-series analysis of the free-surface motion of rotational flow

  Makoto IIMA, Yu IIJIMA, Yuzuru SATO, Yuji TASAKA

  Theoretical and Applied Mechanics Japan 59 187 - 193 1348-0693 2010 [Refereed][Not invited]
   

  We study the free-surface dynamics of rotational flow by time series analysis. In a flow driven by a rotating disk in a cylinder, the free surface irregularly switches between an axisymmetric shape and a nonaxisymmetric shape. This surface switching occurs in combination with significant elevation and elongation of the central part whose height has a strong correlation with the turbulent intensity. Although the number of degrees of freedom for the entire system is considerably large, the surface-shape dynamics indicates that the dimension needed to describe the major motion is much smaller compared with the whole system and the remaining part constitutes noise added to the major part. We have evaluated this conjecture by applying a diagnostic method and have clarified that the time series of the surface height is different from the white noise and the surrogate data of the original time series, both of which have no determinism. © 2011 by National Committee for IUTAM.
• Hydrofoil type of bubble generator for marine drag reduction

  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 一般社団法人日本機械学会 76 (763) 483 - 485 0387-5016 2010 [Not 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.
• Interactive flow field measurement of two savonius windmills

  Akinari Shigetomi, Yuichi Murai, Yuji Tasaka, Yasushi Takeda

  Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 一般社団法人日本機械学会 76 (763) 366 - 368 0387-5016 2010 [Not 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.
• Wake structure of permeable cylinder in stationary and rotating states

  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 一般社団法人日本機械学会 76 (765) 747 - 754 0387-5016 2010 [Not 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.
• Suppression of the flow transition by microbubbles in a taylor-couette flow

  Tomoaki Watamura, Yuji Tasaka, Yuichi Murai, Yasushi Takeda

  Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 一般社団法人日本機械学会 76 (772) 2160 - 2167 0387-5016 2010 [Not 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.
• Breaking wave and bubble generation by a two-dimensional body moving beneath an air-water interface

  Ichiro Kumagai, Yuichi Murai, Yuji Tasaka, Naoya Nakamura

  Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 一般社団法人日本機械学会 76 (772) 2152 - 2159 0387-5016 2010 [Not 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.
• S0502-4-2 Investigation of the flow structure around a baffle in a rectangular open channel by UVP

  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.
• Development of an ultrasonic void fraction profiler

  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.
• Flow transitions in the surface switching of rotating fluid

  Y. Tasaka, M. Iima

  JOURNAL OF FLUID MECHANICS 636 475 - 484 0022-1120 2009/10 [Refereed][Not invited]
   

  We study 'surface switching' quantitatively in flows driven by the constant rotation of the endwall of an open cylindrical vessel reported by Suzuki, lima & Hayase (Phys. Fluids, vol. 18, 2006, p. 101701): the deformed free surface switches between axisymmetric and non-axisymmetric shapes accompanied by irregular vertical oscillation. Detailed simultaneous measurements showed that the magnitude of the velocity fluctuations (turbulent intensity) temporally varies greatly and are strongly correlated with the surface height, suggesting that dynamic switching between laminar and turbulent states is accompanied by vessel-scale surface shape changes. The study also identified clear hysteresis in the turbulent intensity arising from changes in the Reynolds number; the bifurcation diagram consists of two overlapping branches representing a high-intensity (turbulent) state and a low-intensity (laminar) state. Based on the results, a switching mechanism is suggested.
• Turbulent Shear Control with Oscillatory Bubble Injection

  Hyun-Jin Park, Yoshihiko OISHI, Yuji TASAKA, Yuichi MURAI, Yasushi TAKEDA

  J. Phys: Conference Series 147 012037  2009 [Refereed][Not invited]
  
• Frictional drag reduction by wavy advection of deformable bubbles

  Yoshihiko Oishi, Yuichi Murai, Yuji Tasaka, Takeda Yasushi

  Journal of Physics: Conference Series 147 021020  1742-6596 2009 [Refereed][Not invited]
   

  Bubbles can reduce frictional drag in wall turbulence, and its effect is expected to use for ships and pipelines to save their power consumptions. A number of basic experiments have been carried out to date for finding out the best condition for enhancing the drag reduction. One issue that remains at present is the difference of the performance between steady and unsteady status in terms of bubble concentration. All the experiments in the past deal with the steady effect, i.e., the drag reduction is evaluated as a function of mean void fraction or given gas flow rate of continuous injection. Despite to this, the actual phenomena highly depend on local interaction between two phases upon unsteady manner. We focus on this point and elucidate the influence of time-fluctuating void fraction on the total response to the drag reduction. This view is in fact important to estimate the persistency of the bubble-based drag reduction in the flow direction since bubbles formulate wavy advection during their migration. Our experiments are designed to measure the above-mentioned effect from laminar, transitional, and turbulent flows in a horizontal channel. For avoiding the contamination effect that worsens the reproducibility of the experiment, Silicone oil is used as carrier fluid. The oil also simulates the high Weber number bubble condition because of low surface tension. The unsteady interaction between the wavy advection of bubbles and the local skin friction, a synchronized system is constructed to connect the high-speed camera with the shear transducer, which can evaluate the interaction at 1000 fps. From the results, we confirm that the drag reduction is provided at Re> 3000 in the turbulent flow regime, and also the total drag reduction is enhanced by the presence of the waves. © 2009 IOP Publishing Ltd.
• Mode transition in bubbly Taylor-Couette flow measured by PTV

  K. Yoshida, Y. Tasaka, Y. Murai, T. Takeda

  Journal of Physics: Conference Series 147 012013  1742-6596 2009 [Refereed][Not invited]
   

  The drag acting to the inner cylinder in Taylor-Couette flow system can be reduced by bubble injection. In this research, relationship between drag reduction and change of vortical structure in a Taylor-Couette flow is investigated by Particle Tracking Velocimetry (PTV). The velocity vector field in the r-z cross section and the bubble concentration in the front view (z-θ plane) are measured. This paper describes the change of vortical structures with bubbles, and the mode transition that is sensitively affected by the bubbles is discussed. The bubbles accumulate in the three parts relative to vortex position by the interaction between bubbles and vortices. The status of bubble's distribution is different depending on position. This difference affects mode transition as its trigger significantly. The presence of bubbles affects the transition from toroidal mode to spiral mode but does not induce the transition from spiral mode to toroidal mode. Further we found that Taylor vortex bifurcates and a pair of vortices coalesces when the flow switches between spiral mode and toroidal mode. © 2009 IOP Publishing Ltd.
• Wake structure of circular cylinder in microbubble mixture

  T. Suzuki, Y. Oishi, Y. Murai, Y. Tasaka, Y. Takeda

  Journal of Physics: Conference Series 147 012012  1742-6596 2009 [Refereed][Not invited]
   

  Injecting microbubbles near wall can reduce the frictional drag. While it has been confirmed by a variety of experiments to date, the fluid dynamics mechanism of drag reduction has not been comprehensively understood so far. We measure the wake structure of a circular cylinder in microbubble mixture to figure out the characteristic of the interaction between microbubbles and liquid flow accompanying high turbulence. The flow field is restricted to be two-dimensional by confining the bubbly two-phase flow into a thin horizontal channel of 2 mm in height. Microbubbles around 100 μm in diameter are generated with water electrolysis at far upstream the measurement section. Experiment is conducted at Reynolds number higher than 104 to clarify the role of microbubbles in highly turbulent situation. We use solid particles as the PTV-tracer in the single-phase flow and assume that microbubbles trace the liquid flow in the microbubble mixture. We measure the turbulent intensity and Reynolds shear stress distribution from the PTV data and demonstrate that microbubbles significantly suppress the turbulence. In addition, the Karman vortex shedding frequency, which is measured from the unsteady stream function, increases when microbubbles are mixed. © 2009 IOP Publishing Ltd.
• Development of 3-D trajectory measurement system for birds using stereoscopic photography

  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 [Not 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.
• Ultrasonic doppler measurement of bubble-containing turbulent boundary layer beneath a large ship

  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 一般社団法人日本機械学会 75 (751) 538 - 540 0387-5016 2009 [Not 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.
• S0501-3-2 Deformation of an interface between immiscible two liquid layers by a rotating lid

  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.
• J0502-1-4 Interpretation on Periodic Transition between Spiral-Toroidal Modes in Taylor-Couette Bubbly Flow

  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.
• Dilatation and pattern formation of cells in internally heated convection

  Y. Tasaka, K. Yonekura, Y. Takeda, T. Yanagisawa

  JOURNAL OF VISUALIZATION 11 (3) 213 - 220 1343-8875 2008/07 [Refereed][Not invited]
   

  The dilatation and the pattern formation of convection cells in natural convection driven by internal heat generation, first investigated during the 1970s, are reexamined in this paper using an improved experimental apparatus in order to reduce uncertainties as much as possible. The convective motion in the fluid layer was visualized using reflecting particles (Kalliroscope). Cell dilatation was confirmed in the improved experimental apparatus and then investigated quantitatively by extracting the pattern wavenumber from Fourier analysis of the images recorded by a digital camera. The pattern wavenumber was found to decrease with increasing Rayleigh number. We compare our results with earlier investigations and discuss the influence of the thermal boundary condition at the bottom of the fluid layer on the variation of the wavenumber. Two different structures were observed in the same fluid layer at a relatively high Rayleigh number; an additional cell appears in the original cell (Double cell structure) and the descending flow region around the center of the cell expands laterally like a spoke of wheels (Spoke-like structure). Factors for the formation of such complex structures are discussed.
• Velocity vector profile measurement using multiple ultrasonic transducers

  Hironari Obayashi, Yuji Tasaka, Seiji Kon, Yasushi Takeda

  FLOW MEASUREMENT AND INSTRUMENTATION 19 (3-4) 189 - 195 0955-5986 2008/06 [Refereed][Not invited]
   

  This paper proposes a new technique that enables the measurement of the velocity vector in multi-dimensions on a line of the flow field. A system to achieve this goal was developed based on the ultrasonic velocity profiling by using multiple transducers. A two-dimensional system was constructed and successfully applied to an actual flow field for two-dimensional velocity vector measurements. To estimate the influence of the existence of a wall, acoustic field under the developed system was calculated by solving two-dimensional wave equation and then the focal point of an ultrasonic beam was determined to optimize the system. The system was applied to measure the two-directional velocity components of a periodic velocity fluctuation in the wake of a cylinder as an example of unsteady flow. Temporal variation of velocity vector profiles well represent the velocity fluctuation, and vorticity distribution, which is obtained from the spatial distribution of velocity vector, well represents the vertical motion in the wake. (c) 2008 Elsevier Ltd. All rights reserved.
• Ultrasonic visualization of thermal convective motion in a liquid gallium layer

  Yuji Tasaka, Yasushi Takeda, Takatoshi Yanagisawa

  FLOW MEASUREMENT AND INSTRUMENTATION 19 (3-4) 131 - 137 0955-5986 2008/06 [Refereed][Not invited]
   

  For low Prandtl number fluids including liquid metals, optical methods cannot be utilized to visualize convective motion, and in this paper the velocity profile in a liquid gallium layer was measured using ultrasonic velocity profiling, UVP The applicability of the measurement system was confirmed with the rotating flow of liquid gallium and in the natural convection appearing in a glycerol solution layer. The vessel for the liquid gallium layer was optimized for the acoustic properties of liquid gallium. The measured velocity profile shows a cell like convective motion. The spatio-temporal behavior of large-scale convective motion in turbulent convection was observed as a temporal variation of the velocity profile with two kinds of periodic fluctuations of the convection cell. (c) 2007 Elsevier Ltd. All rights reserved.
• Visualization of a rotating flow under large-deformed free surface using anisotropic flakes

  Y. Tasaka, K. Ito, M. Iima

  JOURNAL OF VISUALIZATION 11 (2) 163 - 172 1343-8875 2008/04 [Refereed][Not invited]
   

  This study aims to clarify the relationship between the deformation of a free surface and flow transition in a "switching phenomenon" process. In a flow driven by a rotating disk in a cylindrical open vessel, the free surface irregularly changes its shape from axisymmetric to nonaxisymmetric and vice versa with repeating up-and-down motion (so-called "switching phenomenon"). The flow under the free surface was visualized by anisotropic flakes. When the free surface assumes a parabolic shape, the flow is distinguished by three regions; local circulation region, rigid vortex region and meridional circulation region. The flow transition in the switching phenomenon was shown by snapshots and movies of the visualized flow; the flow near the free surface is laminar even if the shape of the free surface changes to nonaxisymmetric during the time at which the free surface attaches to the bottom of the vessel. After the free surface detaches from the disk, the flow near the free surface becomes turbulent. When the free surface changes to axisymmetric while descending to the bottom, the flow changes from turbulent to laminar flow and the local circulation region reemerges at the center of the vessel.
• Particle tracking velocimetry applied for fireworks - A demonstration of vector field measurement in hundreds meter space

  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.
• 1727 Measurement of visco-elastic effect in polymer solution by means of UVP

  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.
• A statistical study of spots in torsional Couette flow

  Patrice Le Gal, Yuji Tasaka, Jotaro Nagao, Anne Cros, Kohei Yamaguchi

  JOURNAL OF ENGINEERING MATHEMATICS 57 (3) 289 - 302 0022-0833 2007/03 [Refereed][Not invited]
   

  This article presents some results on the statistical behavior of localized structures-called "spots"-that propagate in the flow between a rotating and a stationary disk when those are very close one to the other. Under these conditions the rotating-disk flow belongs to the Couette-flow family and is called the torsional Couette flow. Some visualizations of its transition to turbulence have already revealed the propagation of these spots (Schouveiler et al., J Fluid Mech 443:329-350, 2001) from the rim of the disk towards its center. Using flow visualizations and an original image analysis, the present study aims to better describe the characteristics of the spots whose number continuously increases with the Reynolds number until they invade the whole flow. Moreover, we propose a statistical model that predicts an error-function shape for the probability to observe a spot at a given radial position. This prediction is confirmed by an image analysis of the flow and the stability curve of torsional Couette flow is deduced from these observations.
• Visualization of Slug Flows Using Visible Backlight CT

  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
• PIV for wake structure behind an object by means of micro soap bubble

  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.
• Ultrasonic measurement of thermal plume appearing in transparent and opaque liquids

  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.
• Ultrasonic Measurement of a Rotating Flow under Free Surface

  TASAKA Yuji, IIMA Makoto, ITO Kentaro

  Transactions of Visualization Society of Japan The Visualization Society of Japan 27 (1) 269 - 270 0916-4731 2007 

  A rotating flow accompanying free surface shows aperiodic switching between an axisymmetric surface shape and a nonaxisymmetric surface shape at a certain Reynolds number. This study aims to clarify a relation between the surface shape switching and flow transition. Ultrasonic velocity profiling was utilized to measure instantaneous velocity profile of the rotating flow. Variation of the turbulent intensity with respect to Reynolds number shows a flow transition at the same Reynolds number for the switching. The variation also shows a change of a tendency which expresses flow instability occurring at a smaller Reynolds number.
• PTV measurement of flows around airfoil with soap bubble tracer

  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.
• PTV measurement of interaction between bubbles and longitudinal vortices

  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.
• Hysteretic mode exchange in the wake of two circular cylinders in tandem

  Yuji Tasaka, Seiji Kon, Lionel Schouveiler, Patrice Le Gal

  PHYSICS OF FLUIDS 18 (8) 084104  1070-6631 2006/08 [Refereed][Not invited]
   

  Our experimental study is devoted to the analysis of the flow past two tandem circular cylinders near the vortex shedding threshold. A recent bidimensional numerical analysis of this flow [Mizushima and Suehiro, Phys. Fluids 17, 104107 (2005)] has predicted that the bifurcation diagram should become complex in the vicinity of the instability threshold. Subcritical and saddle node bifurcations that lead to hysteretic exchanges between two different modes of vortex shedding were detected for particular distances of separation of the cylinders. We present here visualizations and velocity measurements of this flow in a water channel that prove the robustness of the complexity of the bifurcation diagram in real flows. (c) 2006 American Institute of Physics.
• Environmental Flow Measurement Using Ultrasonic Velocity Profiler

  YOKOYAMA Kaoru, KOJIMA Shinya, OHKUBO Tomoyuki, TASAKA Yuji, TAKEDA Yasushi, YOSHIDA Shizuo

  Transactions of the Japan Society of Mechanical Engineers. B 一般社団法人日本機械学会 72 (719) 1694 - 1701 0387-5016 2006/07/25 [Not refereed][Not invited]
   

  Ultrasonic Velocity Profiler (UVP) was applied to an environmental flow attempting an efficient measurement of river flow. In a lab-scale open channel, a velocity distribution in a channel cross section was obtained and a flow rate was estimated. We confirmed that the flow rate in an open channel can be measured with an accuracy as high as 5%. It was also established to detect the bottom position from a single velocity distribution, which might give us information about the geometry and condition of the bottom surface of the channel. We practiced the method in a small river, and showed that...
• Measurement of Liquid Metal Flow using Ultrasonic Velocity Profiler : 2nd Report, Visualization of Thermal Convective Motion in Liquid Gallium Layer

  TASAKA Yuji, YANAGISAWA Takatoshi, YAMAGISHI Yasuko, YOSHIDA Masataka, TAKEDA Yasushi

  Transactions of the Japan Society of Mechanical Engineers. B 一般社団法人日本機械学会 72 (718) 1559 - 1565 0387-5016 2006/06/25 [Not refereed][Not invited]
   

  Thermal convection in liquid gallium layer was investigated as a fundamental study for Rayleigh-Benard convection in low Prandtl number fluid using ultrasonic velocity profiler, UVP. Temperature dependence of sound speed in liquid gallium was measured for a velocity profile measurement by UVP. Measured velocity profiles visualized a convective motion in the liquid gallium layer, and it is a roll shape motion. Spatio-temporal velocity profile showed that there are two types of spatial fluctuation of the convection roll, and there are 3 modes on the number of convection rolls in the fluid lay...
• Measurement of Liquid Metal Flow using Ultrasonic Velocity Profiler : 1st Report, Flow Measurement of LBE Target

  OBAYASHI Hironari, TASAKA Yuji, MORINAGA Masato, TAKEDA Yasushi, KIKUCHI Kenji

  Transactions of the Japan Society of Mechanical Engineers. B 一般社団法人日本機械学会 72 (715) 642 - 648 0387-5016 2006/03/25 [Not refereed][Not invited]
   

  Ultrasonic Velocity profiler (UVP) is a powerful tool to measure an instantaneous velocity profile especially on a velocity measurement of an opaque liquid flow, such as liquid metal. In this study, UVP is applied to a velocity field measurement of a fluid flow of Lead Bismuth Eutectic (LBE) in the Accelerator Drive System (ADS). At a lower temperature, wetting of LBE to stainless steel that is a material of target loop is too poor. We solved this problem by solder coating of the measurement window of the target loop. We performed velocity measurement on the centerline of the loop and confi...
• Turbulent Bubbly Channel Flow Investigated by Ultrasound Velocity Profile

  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.
• 2420 Behavior of Turbulent Spot in the Flow between Stationary and Rotating Disks

  TASAKA Yuji, Le Gal Patrice, TAKEDA Yasushi

  The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2006 159 - 160 2006 

  Flow between stationary and rotating disks, which is called as the tortional Couette flow, was investigated experimentally as a family of Couette flow including Taylor-Couette flow. Behavior of turbulent spot appearing in the flow was observed and its shape, similar to hose-shoe vortex appearing in the turbulent boundary layer, convection and disappearance were explained from the obtained images visualized by Kalliroscope flakes. Statistical analysis to determine the stability curve for the spot was performed based on visualized images. Using image analysis, the number of spot at each radius was counted as the number of black pixels for several rotating speed. Probability distribution for spot existing determined form the obtained number has similar form with the mathematical model constructed under some assumptions.
• 4418 Ultrasonic Measurement of Water Distribution on Gas Diffusion Layer in Polymer Electrolyte Fuel Cell

  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.
• Visualization of Liquid Metal Flow by Ultrasound Doppler Method

  OBAYASHI Hironari, TASAKA Yuji, TAKEDA Yasushi

  Transactions of Visualization Society of Japan The Visualization Society of Japan 26 (103) 252 - 257_1 0916-4731 2006
• Introduction of Recent Techniques in Ultrasonic Visualization of Opaque Materials

  TASAKA Yuji

  Transactions of Visualization Society of Japan The Visualization Society of Japan 26 (103) 251 - 251 0916-4731 2006
• 超音波流速分布計測法による液体金属流動計測

  大林寛生, 田坂裕司, 森永聖人, 武田 靖, 菊地賢司

  日本機械学会論文集B編 72 (715) 82 - 88 2006 [Not refereed][Not invited]
  
• Oscillating Taylor-Couette flow

  MORIMAGA Masato, TAKADA Daisuke, TASAKA Yuji, TAKEDA Yasushi

  Journal of Japan Society of Fluid Mechanics 日本流体力学会 24 (2) 185 - 194 0286-3154 2005/04/25 [Not refereed][Not invited]
   

  We attempted a direct energy injection to a higher flow mode of Taylor-Couette flow directly by using modulated rotating speed of an inner cylinder. Targeting mode is wavy vortex flow (WVF) and then a characteristic frequency of WVF is set to a base 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. As the results, this method cannot realize a direct energy injection, and energy of WVF is reduced by the modulated rotation. Th...
• Effects of heat source distribution on natural convection induced by internal heating

  Y Tasaka, Y Takeda

  INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 48 (6) 1164 - 1174 0017-9310 2005/03 [Refereed][Not invited]
   

  The effects of a heat source distribution on natural convection induced by internal heating are studied by using simplified models of the distribution. A linear stability analysis is made to study the effects on critical Rayleigh number and critical wavenumber. The total amount of heat generation to set convection and the asymmetry in the convective motion are discussed for two extreme cases of heat source distribution. Effect of additional bottom wall heating is also investigated on the critical condition and the asymmetry of the convective motion. (C) 2004 Elsevier Ltd. All rights reserved.
• 306 Analysis of Liquid Metal Flow for LBE Target

  OBAYASHI Hironari, MORINAGA Masato, TASAKA Yuji, TAKEDA Yasushi, KIKUCHI Kenji

  The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2005 203 - 204 2005 

  Ultrasonic Velocity Profiler (UVP) is a powerful tool to measure an instantaneous velocity profile especially on a velocity measurement of an opaque liquid flow, such as liquid metal. In this study, UVP is applied to a velocity field measurement of a fluid flow of Lead Bismuth Eutectic (LBE) in Accelerator Drive System (ADS). We performed velocity measurement on the centerline of the loop and confirmed basic performance of the loop. It was found that there was intermittent release of eddy from the re-circulation region formed on a wall surface of an inner cylinder and behind the edge. We made then a measurement for an angular direction of circumference around the central axis and observed 3-dimensional structure of LBE flow of the loop. From these results, we made clear that UVP is highly effective in a measurement of the flow field of liquid metal.
• 310 Visualization and Analysis of Temperature Field on Internally Heated Convection

  TASAKA Yuji, KUDOH Yohichi, YANAGISAWA Takatoshi, TAKEDA Yasushi

  The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2005 211 - 212 2005 

  Natural convection in a shallow fluid layer induced by internal heat generation was investigated experimentally. A horizontal temperature field at each Rayleigh number was visualized by Thermo-chromic Liquid Crystal (TLC), and then the obtained images were converted to the temperature field by a calibration curve, which correlates between color information extracted from the image and temperature. Individual cells were extracted from the converted temperature field and a variation of area of the cells with respect to the Rayleigh number represented a cell dilatation. Variations of statistical values, standard deviation of the temperature field and mean size of a cell, with Rayleigh number increases showed that there might be a gradual transition of the convection.
• 307 Ultrasonic Visualization of Convection Motion in Liquid Gallium Layer

  YOSHIDA Masataka, TASAKA Yuji, YANAGISAWA Takatoshi, TAKEDA Yasushi

  The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2005 205 - 206 2005 

  Natural convection induced by a vertical temperature gradient in a slab shape container filled with liquid Gallium is investigated experimentally. An instantaneous velocity profile in the fluid layer was measured using UVP (Ultrasonic Velocity Profiler), which can be used for opaque fluid such as liquid metal. The results represent a convective flow pattern and its temporal fluctuation. There are some situations, where 2, 3 or 4 convection rolls appear, on the visualized convective motion. A variation of the number of rolls is shown by spatio-temporal velocity map. Simultaneous velocity profile measurement using two ultrasonic transuducers indicates axial fluctutation of the rolls.
• Measurement of Gas-liquid Two-phase Horizontal Pipe Flow Using UVP

  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.
• Absolute instability analysis of the vortical structure in the rectangular plate wake

  Yuji Tasaka, Hitoshi Ishikawa, Osamu Mochizuki, Masaru Kiya

  Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 一般社団法人日本機械学会 70 (691) 586 - 593 0387-5016 2004 [Not refereed][Not invited]
   

  Vortical structures in the wake of the axisymmetric bluff body were investigated using an absolute instability analysis. The wake of the rectangular plate has different frequency components for vortical structures in major and minor planes. On the condition that the flows in both planes are parallel individually, the absolute instability analysis revealed that the unstable frequency obtained showed a good agreement with the shedding frequency of the hairpin shape vortex in the minor plane. In the major plane, it was found that an other frequency component related to the meandering vortex structure was also associated with the unstable instability. In an analysis of the major plane, it was shown that there are two saddle points in the complex field which express the dispersion relation.
• Statistical properties in the wake of a rectangular plate

  Yuji Tasaka, Hitoshi Ishikawa, Osamu Mochizuki, Masaru Kiya

  Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 一般社団法人日本機械学会 69 (679) 568 - 573 0387-5016 2003 [Not refereed][Not invited]
   

  Wake properties of a rectangular plate with aspect ratio AR of 2 and 3 are investigated experimentally to identify statistically. It is characteristic of the near wake of a rectangular plate that mean velocity profile has two inflection points on the major-axis. One of the inflection points is yielded by the vortex shedding and the other is located within the recirculation region. The growth rate of a half width on the minor-axis is greater than that of the axisymmetric bluff bodies, such as a sphere and a circular disk, it follows the growth rate of a half width of the two-dimensional wake. The reduction rate of the maximum velocity defect is also greater than wakes of axisymmetric and two-dimensional bluff bodies. These wake properties of a rectangular plate are similar with that of an elliptic wake with the same AR. However, the existence of the corner of a rectangular plate, which is the geometrical difference between the rectangular and elliptic plate, only affected the maximum turbulent intensity on major axis.
• Turbulent Structure in the Wake of a Rectangular Plate

  TASAKA Yuji, ISHIKAWA Hitoshi, MOCHIZUKI Osamu, KIYA Masaru

  The proceedings of the JSME annual meeting 一般社団法人日本機械学会 2000 209 - 210 2000 

  Near wake of a rectangular plate with aspect ratio of 2 and 3 is investigated experimentally. For both ratios the axis switching occurs the further downstream compared with that of the elliptic disk, while the grouth rate of half width is almost the same. The wake of the rectangular plate is similar to that of an elliptic disk with the same aspect ratio. This means that whether the comer of body is round or sharp is not essential to the near wake structure. Moreover, the frequency analysis showed that there are two dominant frequencies in these wakes, their Strouhal numbers being dependent on the aspect ratio. Strouhal number of the rectangular plate is smaller than that of the elliptic disk because vortex formation region is longer than that of the elliptic disk.

MISC

• 速度分布情報を基にした食品の流動性評価—特集 おもしろいフルードパワーの最先端(2)

  田坂 裕司, 大家 広平, 西塚 大悟, 芳田 泰基, 熊谷 聡美, 千葉 春子  油空圧技術 / 油空圧技術編集委員会 編  63-  (9)  23  -28  2024/09
• 速度分布計測を基にした食品レオロジー物性の評価

  田坂裕司, 田坂裕司, 大家広平, 高野哲秀, 芳田泰基  日本バイオレオロジー学会誌(Web)  37-  (2)  2023
• 流動計測支援型レオメトリによる食品開発・製造のDX推進

  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
• 流動計測支援型レオメータを用いた複雑流体の管内流れ予測

  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
• 超音波インラインレオメータによる擬塑性流体の粘性評価

  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
• 貯蔵タンク内で流体のレオロジー物性を評価するレオメータの開発

  芳田泰基, 大家広平, 田坂裕司  化学工学会年会研究発表講演要旨集(CD-ROM)  88th-  2023
• レオロジーマップによる高分子溶液の多角的粘弾性評価

  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
• 超音波流速分布計測による過渡的レオロジー物性の評価

  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)  86th-  2021
• Efficient Air Lubrication Method on a 36-m-long Flat Plate Model Employing Repetitive Bubble Injection

  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
• Application of PIV-based pressure field estimation for wind tunnel and water tank experiments

  Y. Murai, Y. Tasaka, H.J. Park  The Japanese Society for Experimental Mechanics  20-  87  -94  2020  [Not refereed][Invited]
  
• Visualization of artificial void waves in bubbly drag reduction experiments using a 36-m-long flat plate

  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
• Wall shear stress fluctuation in bubbly drag reduction for a 36-m-long flat plate

  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
• Applicability Evaluation of In-line Rheometer based on Ultrasonic Velocity Profile Measurements

  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
• Effective viscosity evaluation on separating oil-water mixture by ultrasonic spinning rheometry

  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
• Effective viscoelasticity affected by dispersed particles in non-Newtonian fluid under unsteady shear

  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
• 超音波流速分布計測を用いた複雑流体のレオロジー物性評価—Rheological Evaluations of Complex Fluids by Ultrasonic Velocity Profiling—特集 流動による流体の内部構造変化の可視化

  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
• Non-invasive Inline Rheometer using Ultrasonic Velocity Profiler

  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)  97th-  2019
• Robustness of Savonius turbine for inflow of isotropic turbulence

  MURAI Yuichi, Otomo Shuji, TASAKA Yuji, Denissenko Petr  The Proceedings of the National Symposium on Power and Energy Systems  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.
• Frictional drag reduction promoted by generating void waves in high-speed turbulent channel flows

  TANAKA Taiji, PARK Hyun Jin, TASAKA Yuji, MURAI Yuichi, KAWAKITA Chiharu  The Proceedings of the National Symposium on Power and Energy Systems  2019-  (0)  A122  2019  [Refereed][Not invited]
  
• Rheological evaluation on liquid with dispersion bubbles under shear flow conditions

  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]
  
• 回転式超音波レオメトリを用いた粘土懸濁液のレオロジー評価

  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]
  
• Rheological evaluation of non‐Newtonian effects on Newtonian fluid with dispersed bubbles

  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]
  
• Ultrasonic measurement of milk products flowing in stainless steel pipe

  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>
• Ultrasonic spinning rheometry

  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]
  
• Effect of Microbubbles on the Creation of Localized Turbulence in a Circular Pipe Flow

  中村 幸太郎, 田坂 裕司, 村井 祐一  混相流 = Japanese journal of multiphase flow  30-  (5)  20  -28  2017/03
• Turbulent eddy viscosity in microbubble suspension evaluated by ultrasound spinning rheometry

  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]
  
• 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]
  
• Flow Metering of Multiphase Pipe Flows by Means of Ultrasound Doppler Method

  村井 祐一, 田坂 裕司  化学工学  80-  (8)  468  -471  2016/08
• Rheometry Utilizing Ultrasonic Velocity Profiler : Importance of Flow Measurement and Propositions

  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]
  
• Measurement of rheological properties of fluid foods based on ultrasonic velocity profiling-Novel measuring methodology of spatial viscosity distributions-

  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]
  
• Visualization on the coupling of natural convection in three-density stratifications

  SATO Shu, TASAKA Yuji, MURAI Yuichi  The Proceedings of Conference of Hokkaido Branch  2016-  61  -62  2016
• An Experimental Study on a Savonius Turbine in a Turbulent Flow

  Shuji OTOMO, Susumu OSUKA, Yuji TASAKA, Yuichi MURAI, Petr DENISSENKO  The Proceedings of Conference of Hokkaido Branch  2016.54-  (0)  79  -80  2016
• 浮上する気泡群の数密度構造と液相の速度場構造の相互作用について

  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]
  
• 線形粘弾性解析による分散気泡液体のレオロジー評価

  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]
  
• Toward understanding global flow structure

  Makoto Iima, Takayuki Yamaguchi, Takeshi Watanabe, Akane Kawaharada, Yuji Tasaka, Erika Shoji  Springer Proceedings in Mathematics and Statistics  183-  139  -158  2016  [Refereed][Not invited]
   

  Flows in nature are generally coupled with the environment. Also, flow structures in the forms of convection rolls, vortices, boundary layers, for example, are often coupled with flow structures in other form(s) as well as the external environments such as the boundary motion and the temperature gradient. Whole flow structure in such cases is often characterized by multi-scale or hierarchy, therefore, we will term such flow structures "global flow structure". Clearly, the global flow structure is complex in both space and scales, but there are general viewpoints applicable to this category of the flow, by which we can tackle with new phenomena. In this review, we discuss the global flow structure in both views of typical problems and analysis methods itself.
• 0601 Visualization of bubble behavior beneath a model ship in large towing tank experiments

  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.
• 1702 Experimental study of convection driven by a bubble plume in background rotation

  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.
• 1703 Numerical analysis and visualization of mist behavior in a horizontal pipe

  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.
• J0510102 Three dimensional flow visualization of wake structure behind of a twisted Savonius turbine

  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.
• J0510104 Stress field visualization of flow around a wing in viscoelastic fluids

  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]
  
• 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]
  
• 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]
  
• Measurement of Mass Diffusion and Turbulent Transition in Natural Gas Pipeline(In-situ fluid mechanics experiments)

  Tomoaki TAKEUCHI, Yuji TASAKA, Pipeline Technology Center Tokyo Gas Co. Ltd., Factory of Engineering Hokkaido University  ながれ : 日本流体力学会誌 = Journal of Japan Society of Fluid Mechanics  34-  (3)  233  -239  2015/06/25
• 超音波流速分布計を用いた分散混相流体の複素粘度診断

  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]
  
• 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]
  
• 0215 Clustering of mono-dispersive bubbles in a horizontal channel flow

  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
• 0213 Flow visualization of a gyromill type bubble generator

  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.
• 0520 On far wake characteristics of a horizontal axis wind turbine and permeable disks

  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.
• 0202 Development of a 3D mist distribution measurement technique by Multi-layer Color PIV

  YONEZAWA Norio, OISHI Yoshihiko, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2014-  "0202  -1"-"0202-2"  2014/10/25  

  In order to measure three-dimensional flows in large atmospheric space, we have developed a new PIV system based on Multi-layer Color PIV. This new system allows us to determine the six-layer three-dimensional velocity vector fields at a given frame rate just using a single camera view by color coded volumetric projection of light. In this paper, we developed the prototype system, and verified it by simulation of artificial 3D smoke. This system estimates the six-layer two components velocity field in three-dimensional vector field. As the result of verification, reconstructed layers and determined vectors have high correlation value with theoretic image and vector field, around the center of measurement volume. On the other hand, two problems were found. One is a fragility of pattern matching system for strong velocity gradient field. The other is increase of layer reconstruction error against low luminance pixels.
• 0205 Flow mechanism visualization of thermal destratification in a dam by a bubble plume

  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.
• J0540301 Development of bird image detection system for prevention of wind turbine birdstrikes

  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.
• J0510202 3-D airflow structure visualization by means of multi-layer coloring of smoke-wire technique

  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.
• J0510201 PTV-based Lagrangian pressure field measurement

  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.
• 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]
  
• 0623 On periodic fluctuation of wake behind a permeable disk

  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.
• 0312 Maintained void rate fluctuation by periodic bubble injection

  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.
• 0202 Destruction of broad density stratification by means of a bubble plume

  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.
• 0201 Large deformation characteristics of a droplet in oscillating shear flow

  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_.
• 0214 Monitoring of gas-liquid two-phase flows in a horizontal channel with Ultrasonic Velocity Profiler

  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.
• 0215 Optimization of a hydrofoil bubble generator for ship drag reduction

  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.
• Effective Viscosity of Bubbly Liquid Accompanied by Non-Equilibrium Bubble Deformations

  T.KIMURA, T.SHIRATORI, Y.OISHI, I.KUMAGAI, Y.TASAKA, YMURAI  The 12th International Symposium on Fluid Control, Measurement and Visualization (FLCOME2013)  OS8-03-1, USB  2013/11  [Refereed][Not invited]
  
• 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]
  
• 1064 SIMULTANEOUS MEASUREMENTS OF VELOCITY AND TEMPERATURE FIELDS MODIFIED BY A THERMAL BLOB INJECTING INTO A LIQUID METAL LAYER

  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.
• J054012 Measurement of Flow Structure around a Wind Tunnel Model VAWT by PIV

  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.
• J054021 Spatial reconstruction of flow field induced in rotating system using off-axis measurement

  MURAI Yuichi, SHIRATORI Takahisa, TASAKA Yuji, Vlaskamp Jop  Mechanical Engineering Congress, Japan  2013-  "J054021  -1"-"J054021-5"  2013/09/08  

  Measurement of velocity distribution in flows requires multi-dimensional setup when the flow behaves on fully three-dimensional and unsteady manner. Experimentalists, therefore, often need an effort to acquire the quantitative flow field information with limited instrumentation that only measure flow velocity in partial dimension or restricted components. UVP (ultrasound velocity profiling technique) and PIV (particle image velocimetry) are categorized to 1C-1D and 2C-2D velocity measurement as their first principle while extension of the system for upper dimensional measurement is ongoing for the both cases. In this study, the methodology of the application of UVP and PIV to three-dimensional flow field without any introduction of additional hardware system is presented, and demonstrated with several representative flow fields which show unique features of rotating fluid mechanics. The method is commonly based on off-axis measurement of flow field, which allows 3-D flow field to be scanned by relative frame rotation between the velocity profiling line and the rotating flow structure.
• J057015 Influences of imperfections on a turbulent flow transition in a rotating flow with free surface

  TASAKA Yuji, IIMA Makoto, KAWAHARADA Akane  Mechanical Engineering Congress, Japan  2013-  "J057015  -1"-"J057015-5"  2013/09/08  

  Rotating flows in a cylindrical open vessel show dynamic surface deformations between an axisymmetric and a non-axisymmetric shape accompanied by laminar-turbulent transitions of the global flow structure. Appearance of the dynamic surface deformation, termed surface switching in series of our papers, depends on the apparatus and a more precise system has a tendency to reduce frequency of appearance of the surface switching. The aim of this study is to clarify influences of imperfections of the flow system on the flow transition. We prepared three disks having different gap size against the cylinder wall and an elliptic disk for the rotor with expecting difference on noise generation in the flow system. As our expectation the disk with wider gap increases the appearance of surface switching. And a statistical analysis on the corresponding surface height variation suggests that the surface switching is a random event due to gap flow noise. Using the elliptic disk enhances the flow instability for axi-symmetry breaking on the free surface and leads toward the surface switching. But after the switching occurs, the disk affects to stabilize the surface motion.
• A124 Wind tunnel model experiments on interaction among horizontally arranged VAWTs

  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
• F113 Improvement of Hydrofoil Performance on Air Bubble Entrainment for Drag Reduction of Ships

  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.
• Flow Visualization and Characterization of non-Newtonian fluids by UVP

  白鳥 貴久, 大石 義彦, 田坂 裕司  可視化情報学会誌 = ournal of the Visualization Society of Japan  33-  (1)  411  -414  2013
• 0505 Non-equilibrium deformation of a drop in an oscillatory shear 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.
• 0509 Experimental CFD-hybrid Analysis of a Horizontally Moving Object beneath Water Surface

  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.
• 0504 Plume's rhythm:nonlinear oscillation of the flow in deformable gel beads

  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.
• 0508 Behavior of bubble clustering under a drag reduction condition in a horizontal channel flow

  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.
• 0516 Statistical Measurement of Particle-Gas Two-Phase Turbulent Flow in Horizontal Cylindrical Pipe

  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.
• 305 Visualization of behavior of microbubbles in a boundary layer

  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
• 312 Tidal influence simulation of bubble-drag reduction ship

  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
• 311 Experimental study on a bubble generator with rotating hydrofoils

  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
• J055022 Single Camera-based Global 3-D Particle Image Velocimetry for Airflows

  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.
• 309 Lagrangian Frame PTV on the interference between a free surface and vortex shedding from a circular cylinder

  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
• 311 Detection and distinction of birds for Bird Strike by image analysis

  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
• 310 Reconstruction of 3-D smoke density distribution for Color Particle Image Velocimetry applied to 3-D measurement of airflows

  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
• 316 Assessment for relationships between velocity fluctuations of propeller wind turbine wakes and low-frequency noise

  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
• 314 Rheological parameter estimation for viscoelastic fluids on flow field analyses

  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
• J055015 Visualization of pumping principle of a Trochoid gear pump for Non-Newtonian fluids

  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.
• H102 Optimization of Hydrofoil Air Pump for Reduction of CO_2 Emissions from Ships

  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.
• D203 Control of angle of attack for Darrieus blades by cylindrical elements

  TAKESHIMA Kotaro, TASAKA Yuji, MURAI Yuichi  National Symposium on Power and Energy Systems  2011-  (16)  347  -350  2011/06/22  

  Since Darrieus turbine is omnidirectional against the wind, it has a great essential advantage in turbulent wind environment. However, the disadvantage is known on the starting up in low velocity conditions of the wind, compared with Propeller turbines. In this study, a new technique to improve the efficiency is proposed by providing a large internal cylinder rotating together with the blades, which can control the angle of attack of the blades. The influence of cylindrical diameter on the blade performance is evaluated from the wake of the turbine. The flow field around the blades is measured by Particle Image Velocimetry. Moreover, the change of angle of attack and lift coefficient are calculated from the measured relative velocity vector field. As a result, the change of angle of attack and lift coefficient are improved in a limited range of rotating angle.
• D206 Wind fluctuation field and low-frequency noise formed around vertical axis wind turbines

  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.
• 302 Spatio-temporal development of two-dimensional microbubble plumes

  MIYAGISHIMA Yoshihito, WATAMURA Tomoaki, TASAKA Yuji, MURAI Yuichi  北海道支部講演会講演概要集  2010-  (49)  53  -54  2010/11/07
• 407 Water height detection in open channel flows using ultrasonic velocity profiling

  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
• 0124 Unsteady Aerodynamics of a Turning Blade

  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.
• 0905 Vortex shedding from a moving cylinder beneath a free surface : The behavior of the Strouhal number with water depth

  OYABU Koji, KUMAGAI Ichiro, TASAKA Yuji, MURAI Yuichi  Fluids engineering conference ...  2010-  243  -244  2010/10/29  

  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 15,000 and for Froude number between 0.01 and 3.2. At large Reynolds number (> 10,000), the surface deformation becomes substantial in the downstream of the cylinder and bubble injection is observed. The Strouhal-Reynolds number relationship with gap ratio between 0.25 and 2.0 which shows the period of the vortex shedding becomes long when the gap ratio is small.
• G310 Dynamics of a vortex ring impacting a solid boundary in a rotating fluid

  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.
• 1901 Ultrasonic measurement of rotating flow fields with free surface deformation

  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.
• 1605 Measurement of the viscoelastic flow around a falling sphere

  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.
• 超音波流速分布計による流動モニタリング技術の新展開

  武田 靖, 田坂 裕司, 村井 祐一  化学工学 = Chemical engineering  74-  (8)  381  -384  2010/08/05
• A101 Development of Bell-shaped Compact Type Savonius-Darrius Hybrid Wind Turbine

  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.
• Turbulent Frictional Drag Reduction Promoted by Passive and Active Fluctuation in Void Fraction

  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.
• PIV measurement of 3D structure of Taylor Column

  Nambu Yuichi, Tasaka Yuji, Murai Yuichi, Vlaskamp J. H. A., Thomas P. J.  日本流体力学会年会講演論文集  2010-  170  -170  2010  

  Off axis PIV approach has been introduced to obtain 3 dimension 3 component velocity vector field of Taylor column. This method makes it possible to reconstruct vector field by a single camera setting because its PIV measurement plane surface is slightly offset toward rotating axis. This approach was applied to Taylor Column which has circumferential instability. The fully reconstructed vector field shows the structure of Taylor column twist around the rotating axis as the distance from the disk increase.
• Intermittent bubble injection by the oscillating Jet: the interference between a free surface and flow past a submerged cylinder

  KUMAGAI Ichiro, OYABU Takeshi, TASAKA Yuji, MURAI Yuichi  日本流体力学会年会講演論文集  2010-  17  -17  2010  

  We have conducted laboratory experiments on the flow past a circular cylinder moving at a constant speed U_0 beneath an air-water interface. The vortex street and the free surface profile are visualized for Reynolds number (Re=Ud/v) between 200 and 15,000 and for Froude number (Fr_h=U_0/(hg)^<1/2>) between 0.01 and 3.2 (d and h are the diameter of the cylinder and the distance between the top of the cylinder and the undisturbed water surface, respectively). At large Reynolds numbers (>10^4), the surface deformation becomes substantial in the downstream of the cylinder and intermittent bubble injection by a jet-like flow is observed. We have also investigated variation of the Strouhal-Reynolds number relationship with gap ratio (a=h/d) between 0.25 and 2.0, which shows the period of the vortex shedding becomes long when the gap ratio is small.
• 回転流体自由界面の不規則スイッチングにおける底面-側壁ギャップの影響

  田坂 裕司, 飯間 信, 佐藤 讓  日本流体力学会年会2010拡張要旨集  2010  [Not refereed][Not invited]
  
• 回転流体系実験時系列からのランダム力学系の抽出

  佐藤 讓, 飯間 信, 田坂 裕司  第59回理論応用力学講演会講演論文集  145  -146  2010  [Not refereed][Not invited]
  
• 回転流体における自由表面の遷移動力学の解析

  飯間 信, 飯島 悠宇, 佐藤 讓, 田坂 裕司  第59回理論応用力学講演会講演論文集  143  -144  2010  [Not refereed][Not invited]
  
• 215 CT Visualization with Dome Mirror Camera

  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
• 216 PIV measurement of circumferential flow structure of Taylor column

  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
• 214 Ultrasonic investigation of oscillating pipe flow of viscoelastic fluid

  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
• 212 Interactive Flow of Savonius Turbines Arranged in Horizontal Plane

  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
• 203 Vortex Shedding from a Bluff-body Beneath a Free Surface : Effect of the Shape of the Body on the Surface Distortion and Bubble Generation

  NAKAMURA Naoya, KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  北海道支部講演会講演概要集  2009-  (48)  39  -40  2009/11/28
• 204 Effect of microbubbles on Taylor-Couette flow

  WATAMURA Tomoaki, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  北海道支部講演会講演概要集  2009-  (48)  41  -42  2009/11/28
• 1401 Modification of effective viscosity in bubbly liquid due to bubble deformation

  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.
• 1804 Experimental investigation of flow over a standing baffle using UVP

  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.
• 1802 Ultrasonic flow field measurement of a rotating flow accompanied

  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.
• A Towing-tank Experiment on Dynamics of Air Bubble Introducer for Drag Reduction of Ships : Flow Visualization of Air Entrainment and Bubble Formation by the Flow Past a Cylinder beneath a Free Surface

  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
• D101 Study on Hydrofoil Type Bubble Generator for Drag Reduction of Ship

  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.
• A116 水平配列時のサボニウス風車の相互干渉(垂直軸方向風車の展開・改善・普及,OS2 自然エネルギー)

  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.
• Nine-months Stay at The University of Manchester

  TASAKA Yuji  Japanese journal of multiphase flow  23-  (1)  88  -90  2009/03/15
• Ultrasound Doppler Measurement of Bubbly Turbulent Boundary Layer Beneath Vessel

  MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi, OHTA Shoko, SHIGETOMI Akinari, HINATSU Munehiko  Japanese journal of multiphase flow  23-  (1)  21  -28  2009/03/15
• Effects of surface tension on irregular surface switching of rotating fluids

  TASAKA Yuji, IIMA Makoto  日本流体力学会年会講演論文集  2009-  153  -153  2009  

  This study aims to clarify the influence of surface tension of the fluids on irregular surface switching, which is a temporally irregular change of the free surface shapes in rotating fluids. 1 cSt Silicone oil, whose kinematic viscosity is almost same with water and surface tension is roughly one forth of that, is used as the test fluid to highlight the influence of the surface tension. The surface of the rotating oil shows sloshing ahead of the surface switching instead of the intermittent deformation of the surface shape which was observed in water.
• Development of 2-D velocity field scanner by ultrasonic Doppler

  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
• Relationship between vortex structure and drag reduction in Bubbly Taylor-Couette flow

  YOSHIDA Koji, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan  28-  (2)  13  -14  2008/09/15
• Multi-Layer PIV Measurement of Internally Heated Convection by Color Light Sheet

  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
• 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]
  
• 3-D Measurement of downburst by Color PIV

  KANDA Tetsushi, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl.  28-  (1)  17  -18  2008/07/01
• Cross Sectional Particle Concentration of Laboratory Model Tornado

  YOSHIMOTO Takahiro, MURAI Yuichi, TASAKA Yuji, TAKEDA Yasushi  可視化情報学会誌. Suppl.  28-  (1)  413  -414  2008/07/01
• D203 Development of 3-D Trajectory Measurement System for Birds using Stereoscopic Photography

  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.
• E111 Ultrasonic Doppler Measurement of Bubble-Containing Turbulent Boundary Layer Beneath a Large Ship

  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.
• 回転流れにおける表面大変形の遷移および分岐 (乱流研究の展望 : ブレークスルーを求めて)

  飯間 信, 田坂 裕司, 伊藤 賢太郎  数理解析研究所講究録  1601-  80  -85  2008/06
• Oscillating Taylor-Couette Flow (Azimuthal motion)

  Yasushi Takeda, Masato Morinaga, Yuji Tasaka  15TH INTERNATIONAL COUETTE-TAYLOR WORKSHOP  137-  012002  2008  [Refereed][Not invited]
   

  It has been attempted to inject the energy directly into a higher mode in a rotating Taylor-Couette system by oscillation of inner cylinder. The earlier investigation on the axial and radial velocity components revealed a dip in the excitation function which indicates a energy loss. In contrary, the azimuthal velocity component shows an increase in its excitation curve, which implies a compensation of the energy loss of other components and indicates a possible energy injection into the WVF mode which is a higher mode than TVF mode.
• The behaviour of Couette-Taylor flow in an azimuthal plane

  Yuuta Nomura, Yuji Tasaka, Yuichi Murai, Yasushi Takeda  15TH INTERNATIONAL COUETTE-TAYLOR WORKSHOP  137-  012001  2008  [Refereed][Not invited]
   

  We investigated the behaviour of Couette-Taylor flow in an 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 shows that spatial-temporal behaviour of MWVF on an azimuthal plane: the modulation first appears near the outer cylinder and spreads globally.
• Rotating flow transition related to surface switching

  Yuji Tasaka, Makoto Iima, Kentaro Ito  15TH INTERNATIONAL COUETTE-TAYLOR WORKSHOP  137-  (3)  163  -172  2008  [Refereed][Not invited]
   

  We have investigated quantitatively the recently reported phenomena called "surface switching" that occurs in the flow driven by a rotating disk in an open cylindrical vessel [1]. The deformed free surface abruptly changes from an axisymmetric to a non-axisymmetric shape accompanying with a vertical oscillation at irregular intervals. We have studied the flow transition quantitatively using ultrasonic velocity profiling (UVP). The turbulent intensity shows a transition at the same Reynolds number as that for the surface switching. We find that the fluid-air interface becomes unstable at a smaller Reynolds number than the critical Reynolds number for the surface switching. Effects of the material of the rotating disk on the surface switching is discussed.
• Experimental study of convection cell structure in internally heated layer

  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.
• 50m模型船における船底境界層のUVP計測(所外発表論文等概要)

  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
• 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]
  
• 自由表面大変形を伴う円筒容器内の回転流れの実験および数理的解析

  飯間 信, 田坂 裕司, 佐藤 讓, 眞山 博幸  日本流体力学会年会2008講演論文集  2008  [Not refereed][Not invited]
  
• 102 Relationship between drag reduction and microbubble motion in concentric rotating cylinders(2)

  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.
• 911 Ultrasonic measurement of boundary layer bubble distribution for microbubble drag reduction(2)

  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.
• 912 Development of a multiphase flowmeter by means of Ultrasonic Velocity Profiling(2)

  Gonzalez A. S. Roberta, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2007-  "912  -1"-"912-4"  2007/11/17  

  In this paper the liquid phase velocity and gas-liquid interface information obtained from UVP measurements are used to estimate the flowrate in a multiphase flow pipeline. The interface is found two different approaches ; by locating the maximum echo intensity at every velocity profile and by finding the maximum variance of the velocity values. The results from the echo intensity method show very good agreement with the actual flowrate. The expected average difference between the flowrate predicted by the echo intensity method and the actual flowrate is ± 5%. That between the variance of the velocity values method and the actual flowrate is -19 to 22 %.
• 308 Wake of a permeable circular cylinder(2)

  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.
• 308 Investigation of Magnetic Permeability and Effective-kinematic Viscosity of Liquid Metal in Uniform Magnetic Field

  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
• 307 Extraction of a pitching component of a ship from spatio-temporal velocity distribution

  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
• 309 Measurement of Velocity Distribution in a Cell of Internally Heated Convection

  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
• 円筒容器内における表面大変形を伴う回転流れの実験的研究(乱流と輸送現象:コーヒーカップから宇宙まで)

  飯間 信, 伊藤 賢太郎, 田坂 裕司  数理解析研究所講究録  1567-  132  -140  2007/08
• 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]
  
• Thermal convection in liquid gallium layer with uniform magnetic field

  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.
• Experimental and theoretical analysis on the rotating fluid with large surface deformation in a cylinder

  Ito Kentaro, Iima Makoto, Tasaka Yuji  日本流体力学会年会講演論文集  2007-  153  -153  2007  

  We analyzed the temporal variation of the surface shape of water in an open cylinder driven by constant rotation of the bottom. In a range of Reynolds number, the surface deformation of the order of the container size shows an aperiodic switching between an axisymmetric surface shape and a nonaxisymmetric surface shape. Time-series analysis of the surface height clarify the characteristics of the flow also switches between laminar and turbulent during the switching process. We also analyzed the variation of turbulent intensity with respect to Raynolds number with a different setup using different material. It is found that the transition Reynolds number is shifted significantly, and that the surface shape shows an intermittent destabilization preceding to the transition. To understand the effect of the material difference, we derived an equation which describes the dynamics of the free surface near the bottom by using a thin-film theory.
• Experimental investigation for onset of modulated wave in Taylor-Couette flow

  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.
• Ultrasonic measurement of instantaneous velocity vector profile

  Yasushi Takeda, Yuji Tasaka  FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT AMSE/JSME FLUIDS ENGINEERING SUMMER CONFERENCE VOL 1, PTS A AND B  701  -706  2007  [Refereed][Not invited]
   

  This paper proposes a new technique that enables the measurement of an instantaneous velocity vector profile in multi-dimensions on a line of the flow field. A system to achieve this goal was developed based on ultrasonic velocity profiling (UVP) by using multiple transducers. A focusing transducer, which reduces the effective diameter of ultrasonic beams around the focal point, was used to minimize the spatial uncertainty in the measurement. A two-dimensional system was constructed by using a normal transducer as a receiver and a focusing transducer as both an emitter and a receiver, and successfully applied to an actual flow field, rigid body motion of fluid in a rotating cylinder, for two-dimensional velocity vector measurements. To estimate the influence of existence of an intermediate wall, acoustic field under the developed system was computed by solving two-dimensional wave equation and then the focal point of an ultrasonic beam was determined to optimize the system. The system was applied to measure two dimensional velocity components of a periodic velocity fluctuation in a wake of a cylinder in a shallow channel as an example of unsteady flow. Obtained temporal variation of velocity vector profile confirmed an applicability of the developed system to unsteady flow. The vortex shedding in the wake was well reproduced as in the vorticity distribution, which was computed from the temporal variation of the vector field using Taylor frozen hypothesis. Although a temporal resolution is still not high, we conclude that applicability of the measurement system has been confirmed.
• Dynamics and optics of bubble tracking velocimetry for airflow measurement

  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.
• Environmental flow field measurement by ultrasonic velocity pofiling

  Yuji Tasaka, Yasushi Takeda, Kaoru Yokoyama, Shinya Kojima  FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT ASME/JSME FLUIDS ENGINEERING SUMMER CONFERENCE, VOL 2, PTS A AND B  1237  -1244  2007  [Refereed][Not invited]
   

  Ultrasonic velocity profiling (UVP) was applied to an environmental flow attempting an efficient measurement of river flow with higher accuracy in comparison with current measurement methods. Applicability of the method on measurement of an open channel flow was confirmed in a laboratory experiment; namely, the cross sectional velocity distribution of the channel was measured; the flow rate was obtained by integrating the velocity distribution; this showed high accuracy, around 4 % in relative error. The method detecting the bottom position of the channel from a single velocity profile was also established and was demonstrated by various boundary conditions at the bottom of the channel. Actual river measurements were performed at a creek flowing Out of a small pond in the campus of Hokkaido University; the width of the creek is approximately 1700 mm. Measured velocity distribution at a cross section of the river represents well the flow field. The bottom position of the river detected by the established method corresponds to that measured by a ruler excluding a place covered by waterweed. The flow rate determined by integrating the velocity distribution is in good agreement with that estimated by a weir mounted at the inlet of the river.
• 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

  Hirotaka Takeuchi, Yuichi Murai, Yuji Tasaka, Yasushi Takeda, Hideaki Tezuka, Michitsugu Mori  FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT AMSE/JSME FLUIDS ENGINEERING SUMMER CONFERENCE VOL 1, PTS A AND B  671  -678  2007  [Not refereed][Not invited]
   

  Particle image velocimetry is applied to measurement of airflows around three types of permeable circular cylinders. The experimental model of the permeable cylinder is made of squared meshed sheet rolled in circle. Water mist smoke is used as air tracer, which is generated with dry ice in a chamber to produce fine spatial density fluctuation for guaranteeing the PIV quality. Since the flow involves fluctuation in a very wide wavenumber from the cylinder size to mesh-dependent eddies, calculating brightness spectrum quantitatively assesses the smoke image quality. The experiment is carried out in an open type wind tunnel. The following results are obtained when the measurement results are compared to those of a solid cylinder. 1: The flow just behind the cylinder has forward velocity due to the permeability while the solid cylinder has reverse flow in the wake. This feature relaxes near field excitation of Karman vortex shedding. 2: The reattachment point behind the cylinder displaces several times as the solid case. As a result of the above two phenomena, the peak potion of the turbulence energy appears in the far downstream region as the permeability of the cylinder increases.
• A244 Ultrasonic Detection of Water Distribution in Gas Diffusion Layer of Fuel Cell

  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.
• A243 Velocity Profiling of Ship Surface Flow with Ultrasonic Doppler Method

  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.
• 超音波流速分布計を用いた液体金属の流動計測--液体金属の複雑な流動を捉える

  田坂 裕司, 武田 靖, 大林 寛生  超音波techno  18-  (6)  70  -74,120  2006/11
• 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]
  
• 1103 Hysteretic Mode Exchange in the Wake of Two-Tandem Cylinders(1)

  TASAKA Yuji, KON Seiji, LE GAL Patrice  Fluids engineering conference ...  2006-  "1103  -a"  2006/10/28  

  図1に示すような,流れに対して直列に配置された2円柱の後流では,低レイノルズ数において,間隙比Γ=l/dに依存して2つの異なる流れのモードが現れる.すなわち,2円柱間の流線が閉じ,それらがあたかも一つの楕円柱であるかのように,そのサイズの流れの変動が生じるモード(Slow mode),および上流円柱後流の対称性が崩れ,円柱スケールの変動が生じるモード(Fast mode)である.本研究では,Mizushima & Suehiroによる数値シミュレーションと線形安定性解析により示されたヒステリシス的なモード変化を実験的に検証するとともに,円柱が有限長さを持つことにより生じる3次元効果の影響について述べる.
• 1708 Velocity Vector Profile Measurement using Multiple Ultrasound Transducers(2)

  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.
• 1705 UVP Measurement for Flows Accompanying Free Surface(2)

  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.
• 1705 UVP Measurement for Flows Accompanying Free Surface(1)

  KOJIMA Shinya, TASAKA Yuji, MURAI Yuichi, TAKEDA Yasushi  Fluids engineering conference ...  2006-  "1705  -a"  2006/10/28
• 1708 Velocity Vector Profile Measurement using Multiple Ultrasound Transducers(1)

  Kon Seiji, Yamaguchi Kouhei, Obayashi Hironari, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2006-  "1708  -a"  2006/10/28
• 1711 UVP measurement of gas-liquid two phase flow in a horizontal tube(2)

  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.
• 708 Wall Turbulence Containing Bubbles Visualized by Kalliroscope(2)

  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.
• 513 Environmental Flow Measurement using Ultrasonic Velocity Profiler

  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
• 202 Development of smoke generator for airflow PIV measurement

  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
• 215 Development of Color PIV Systtem for 3-D Airflow Measurement

  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
• 214 Ultrasonic measurement of velocity profile near the bottom of a ship

  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
• 23pXG-14 Transition of free-surface in rotating flow

  Ito Kentaro, Iima Makoto, Tasaka Yuji  Meeting abstracts of the Physical Society of Japan  61-  (2)  187  -187  2006/08/18
• UVP and PTV Measurements of Wall Boundary Layer Containing Bubbles

  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
• Visualization of vortex rings with background rotation

  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
• Ultrasonic Visualization of Fluid Flow of Liquid Metal

  TASAKA Yuji, YANAGISAWA Takatoshi, MURAI Yuichi, TAKEDA Yasushi  可視化情報学会誌. Suppl.  26-  (1)  353  -354  2006/07/01
• Particle Tracking Velocimetry for a Large Flow Phenomenon Demonstrated by Fireworks

  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
• 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]
  
• AM06-14-001 Experimental study of thermal convection in liquid metal layer

  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.
• AM06-11-003 Interfacial instability of rotating liquid-liquid two phase flow

  FUJIMOTO Shuhei, TASAKA Yuji, TAKEDA Yasushi, YOSHIDA Shizuo  日本流体力学会年会講演論文集  2006-  129  -129  2006  

  The aim of this study is to find out an instability mechanism of rotating oil-water liquid-liquid two phase flow. To achieve such purpose, a velocity profile of the rotating flow was analyzed theoretically. The theoretical velocity profile was in agreement with a experimental result.
• AM06-11-004 Relation between surface switching of rotating flow in a cylinder and the laminar-turbulent transition

  Iima Makoto, Tasaka Yuji, Ito Kentaro  日本流体力学会年会講演論文集  2006-  130  -130  2006  

  We study the surface shape of water in an open cylinder driven by constant rotation of the bottom. Around the critical Reynolds number for the laminar-turbulent transition, the surface deformation, which is of the order of the container size, shows an aperiodic switching phenomenon between an axisymmetric shape and a nonaxisymmetric shape. The flow characteristics is examined by flow visualization by Kalliroscope and velocity measurement by ultrasonic velocity profiler.
• AM06-11-002 Energy dissipation in wavy motion of oscillating Taylor-Couette flow

  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.
• AM06-11-001 Experimental investigation on azimuthal motion of Taylor-Couette flow

  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.
• 1015 PTV Measurement of natural convection driven by internal heating of fluids

  Murai Yuichi, Tasaka Yuji, Takeda Yasushi  Fluids engineering conference ...  2005-  155  -155  2005/10/28
• 1104 Ultrasonic Measurement for Taylor-Couette Flow of Liquid Gallium

  KONDOH Takayuki, SATOH Yohei, TASAKA Yuji, TAKEDA Yasushi  Fluids engineering conference ...  2005-  160  -160  2005/10/28
• 505 Investigation on cross-sectional structure of gas-liquid two-phase pipe flows using backlight CT

  Inaba Kazumasa, Ohashi Jyunichi, Tasaka Yuji, Murai Yuichi, Takeda Yasushi  Fluids engineering conference ...  2005-  65  -65  2005/10/28
• 212 UVP Measurement of Phase Distribution and Velocity Profile in a Horizontal Gas-Liquid Two-phase Channel

  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
• Pattern formation in natural convection induced by internal heat generation

  TASAKA Yuji, TAKEDA Yasushi  形の科学会誌 = Bulletin of the Society for Science on Form  20-  (1)  73  -74  2005/06/01
• Visualization of Horizontal Wall Turbulence Containing Bubbles

  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
• Experimental investigation of natural convection induced by internal heat generation

  Y. Tasaka, Y. Kudoh, Y. Takeda, T. Yanagisawa  14TH INTERNATIONAL COUETTE TAYLOR WORKSHOP  14-  168  -179  2005  [Refereed][Not invited]
   

  Dilatation of a convection cell with respect to its Rayleigh number, one of the problems in internally heated convection, was quantitatively investigated by analyzing temperature field in a cell. The temperature field visualized by a Thermo-chromic Liquid Crystal (TLC) expresses the cell dilatation. A calibration system was developed to convert the visualized photographs of the temperature field to the temperature field. A calibration curve correlating color information extracted from the photograph and temperature was determined from the approximately linear temperature distribution in the horizontal fluid layer using the hue method. Photos taken at various internal Rayleigh numbers were converted to the temperature field by the obtained curve. Extracting individual cells from a temperature field achieves a quantitative expression of the cell dilatation as the variation of the wavenumber of the cell with Rayleigh number increases. The temperature profile in a cell shows that high temperature areas appear at the apexes of the cell, largely different from the profile obtained by linear theory.
• Measurement of Liquid Gullium by Ultrasonic Doppler Velocity Profiler

  Tasaka Yuji, Kitaura Hidekazu, Yoshida Masataka, Takeda Yasushi, Yanagisawa Takatoshi  Fluids engineering conference ...  2004-  313  -313  2004/11/24
• E131 Analysis of a temperature field in internally heated convection :

  TASAKA Yuji, KUDO Yoichi, TAKEDA Yasushi, YANAGISAWA Takatoshi  日本流体力学会年会講演論文集  2004-  154  -155  2004  

  Thermal convection in a horizontal fluid layer induced by internal heat generation is investigated experimentally. Thermo-chromic Liquid Crystal (TLC) is used to visualize the temperature field in the fluid layer. Color component of TLC is calibrated and the visualized image is converted to the temperature field. Temperature field for each Rayleigh number determines the convection cell dilatation with respect to the Rayleigh number. Deformation of the cell with increasing the Rayleigh number is shown by the temperature profile in a cell. The critical Rayleigh number at onset of convection is estimated by using a variation of temperature difference in a cell.
• Sound Speed Measurement of PCM Micro Emulsion Slurry

  Didier Vuarnoz, Tasaka Yuji, Takeda Yasushi, Inaba Hideo  Fluids engineering conference ...  2003-  36  -36  2003/09/18
• A new algorithm for low velocity measurement by UVP

  TADATA Norihiko, TAKEDA Yasushi, TASAKA Yuji  Fluids engineering conference ...  2003-  33  -33  2003/09/18
• Spatiotemporal behavior of the precessing jet

  KITAURA Hidekazu, SUGAWARA Yuuki, TASAKA Yuji, TAKEDA Yasushi  日本流体力学会年会講演論文集  2003-  416  -417  2003  

  A continuously unstable precessing flow is formed within a short cylindrical chamber following a large sudden expansion and the jet emerges from nozzle exit leaning and rotating about the nozzle axis. Flow field within the nozzle chamber and the behavior of the external jet have been reported with pressure measurement, visualization and so on. This paper shows characteristics of the precessing jet, a frequency of rotating about the nozzle axis and an angle of emerging jet, using UDM (Ultrasound Doppler Method) which can measure 1-D velocity distribution on a measurement line instantaneously.
• Stability of Natural Convection in a Horizontal Layer induced by Internal Heating : Effect of Distribution of Heat Generation

  TASAKA Yuji, TAKEDA Yasushi  日本流体力学会年会講演論文集  2003-  382  -383  2003  

  A natural convection in a horizontal fluid layer induced by internal heat generation distributed non-uniformly was studied. We considered the heat source distribution to vary exponentially to the vertical direction. Stability of the fluid layer was analyzed in cases that heat source concentrates on the bottom, and on the upper boundary. Variations of critical values, critical Rayleigh number and critical wave number, with respect to the specific scale of the heat source distribution were obtained. The analysis clarified the effects of such heat source distributions on the critical values of the natural convection.
• Experiment on natural convection in a horizontal layer induced by internal heat generation

  KUDOH Yohichi, TASAKA Yuji, YONEKURA Kengo, TAKEDA Yasushi  日本流体力学会年会講演論文集  2003-  384  -385  2003  

  Natural convection induced by intemal heat generation was studied experimentally. We realized internal heat generation by passing electric current through the ionic fluid. The convective flow pattems were visualized by using Kalliroscope. And also the difference from those observed in the Benard configuration was clarified qualitatively.
• Natural Convection in the Horizontal Fluid Layer driven by Internal Heat Generation : 2. Flow Visualization

  YONEKURA Kengo, TASAKA Yuji, KUDO Yoichi, TADATA Norihiko, TAKEDA Yasushi, ISHIKAWA Hitoshi  北海道支部講演会講演概要集  2002-  (42)  38  -39  2002/10/05  

  The natural convection induced by internal heat generation was studied experimentally. We realized internal heat generation by passing electric current through the ionic fluid. The convective flow patterns were visualized by using kalliroscope. And also the difference from those observed in the Benard configuration was clarified qualitatively.
• Natural Convection in the Horizontal Fluid Layer driven by Internal Heat Generation : 1. Stability Analysis

  TASAKA Yuji, YONEKURA Kengo, KUDO Yoichi, TADATA Norihiko, TAKEDA Yasushi, ISHIKAWA Hitoshi  北海道支部講演会講演概要集  2002-  (42)  36  -37  2002/10/05  

  The natural convection induced by internal heating was studied. In order to clarify convective patterns in this phenomenon, we analyzed stability of fluid layers for various profiles of heat generation, H(z). As the result, the influence of the shape of the heat distribution upon the convective pattern was clarified.

Books etc

• 理科総合大百科 2024: ためしてわかる 実験・観察

  『理科教育ニュース』編集部 (Contributorp.113)
  少年写真新聞社 2024/01 (ISBN: 4879817899) 200
• 分散系のレオロジー : 基礎・評価・制御、応用

  鈴木, 洋 (Joint work第I編第２章第５節; 第II編第３章第３節; 第２編第２章第５節)
  エヌ・ティー・エス 2021/08 (ISBN: 9784860437312) ii, viii, 387, xp, 図版21p
• 流れ学 流体力学と流体機械の基礎

  山田英巳, 濱川洋充, 田坂裕司 (Joint work第11章)
  森北出版 2016
• Air and water

  Yasushi Takeda, Yuji Tasaka (Joint work)
  Grand public 2013 (ISBN: 9782759808281)
• Ultrasonic Doppler Velocity Profiler for Fluid Flow

  Yuji Tasaka (Joint editorChapter 2, Sections 4.1, 5.1, 7.2 & Appendi)
  Springer 2012/10 (ISBN: 9784431540267)

Presentations

• Rheometry utilizing ultrasonic velocity profiling  [Invited]

  Yuji Tasaka

  23rd Rheology forum  2021/10
• Effective viscoelasticity affected by dispersed particles in non-Newtonian fluid under unsteady shear

  YOSHIDA Taiki, TASAKA Yuji, MURAI Yuichi

  The Proceedings of the Fluids engineering conference  2020  The Japan Society of Mechanical Engineers
   

  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.

• Liquid metal experiment for elucidating Magneto-Rayleigh-Bénard convection in a square box  [Invited]

  Yuji Tasaka

  Invited lecture, Italian Institute of Technology (Istituto Italiano di Tecnologia - IIT)  2019/09
• Frictional drag reduction promoted by generating void waves in high-speed turbulent channel flows  [Not invited]

  TANAKA Taiji, PARK Hyun Jin, TASAKA Yuji, MURAI Yuichi, KAWAKITA Chiharu

  The Proceedings of the National Symposium on Power and Energy Systems  2019  The Japan Society of Mechanical Engineers
  
• Robustness of Savonius turbine for inflow of isotropic turbulence

  MURAI Yuichi, Otomo Shuji, TASAKA Yuji, Denissenko Petr

  The Proceedings of the National Symposium on Power and Energy Systems  2019  The Japan Society of Mechanical Engineers
   

  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.
• 超音波流速分布計を用いた複雑・混相液状食品の非接触物性計測  [Invited]

  田坂裕司

  第44回食品の物性に関するシンポジウム講演会  2017/09
• urface switching statistics in a rotating fluid: effects of system internal noise  [Invited]

  Yuji Tasaka

  Invited lecture, LIMSI  2017/06
• MHD Rayleigh-Bénard convection confined by a moderate aspect ratio box  [Invited]

  Yuji Tasaka

  Invited lecture, Technische Universität Ilmenau  2016/12

Association Memberships

• THE IRON AND STEEL INSTITUTE OF JAPAN   THE JAPANESE SOCIETY FOR MULTIPHASE FLOW   American Physical Society   THE JAPAN SOCIETY OF FLUID MECHANICS   THE JAPAN SOCIETY OF MECHANICAL ENGINEERS   

Research Projects

• 気液混相乱流境界層の発達過程で現れるボイド波のモデル化とその制御

  日本学術振興会：科学研究費助成事業

  Date (from‐to) : 2024/04 -2028/03 

  Author : 朴 炫珍, 金 相元, 堀本 康文, 田坂 裕司, 村井 祐一
• 非定常レオロジー物性の評価が詳らかにする粒子懸濁液の流動現象

  日本学術振興会：科学研究費助成事業 基盤研究(B)

  Date (from‐to) : 2023/04 -2027/03 

  Author : 田坂 裕司
• Smart control of gas-liquid two-phase turbulent boundary layers for frictional drag reduction

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  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．
• Drag reduction by surfactant additives: functional viscoelasticity and temper ature effects evaluation

  Japan Society for the Promotion of Science：SAKURA program

  Date (from‐to) : 2024/04 -2026/03
• Study on Flow Assurance and Technique Minimizing Pressure Loss for Subsea Ore-lifting

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  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, 田坂 裕司, PARK HYUNJIN

   

  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。
• 混相/複雑流体のレオロジー物性計測を基軸とした流体科学の創成

  国立研究開発法人 科学技術振興機構：さきがけ

  Date (from‐to) : 2021/10 -2025
• 液体金属対流の定量可視化実験から観た地球流体核における熱物質輸送

  日本学術振興会：科学研究費助成事業 基盤研究(C)

  Date (from‐to) : 2020/04 -2023/03 

  Author : 熊谷 一郎, 田坂 裕司, 益子 岳史

   

  本研究課題は、液体金属プルームの温度場と速度場の同時可視化を目的としているが、液体金属内部は可視光では見えないため、まずは既知のサーマルやジェットなどの流れについての流体実験を行い、正しく流速場が計測できているか確認するための実験を行った。温度計測については、これまで使用してきた薄型の矩形水槽の壁面に設置した感温液晶板では、１種類の液晶しか使っていないため、温度の計測範囲が限られてしまうという問題があった。そこで、かつて代表者が開発した複数の感温液晶を用いた温度場の可視化法を本課題でも適用できないか、検討を開始した。 また２重円筒水槽を用いた対流実験については、水および非ニュートン流体を用いたレイリー・ベナール対流実験を行ってきたが、水槽の壁面が曲面となっており、ハレーションなどの影響で、可視化計測がうまくできていない状況となっていた。そこで、紫外レーザーで励起される蛍光粒子を用いた流れ場の可視化法を新たに導入し、予備実験を行なった。その結果、壁面での余計な反射光が見えなくなったため、流体中のトレーサーの励起光のみが観測可能となり、PIV（粒子画像流速計）解析によって詳細な流速場を得ることができた。相変化を伴う流体（感温膨潤性ゲル（PNiPAM）のサスペンジョン）とHele-Shawセルを用いたレイリー・ベナール対流実験においても、この紫外レーザーでの可視化は有効であるため、より精度の高い流れ場解析が可能となった。
• 分散気泡のレオロジーが解き明かす混相乱流遷移のシナリオ

  文部科学省：科学研究費補助金（基盤研究(B)）

  Date (from‐to) : 2019/04 -2023/03 

  Author : 田坂裕司
• Smart control of gas-liquid two-phase turbulent boundary layer

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2017/04 -2022/03 

  Author : Murai Yuichi

   

  In this project, a variety of experimental approaches were taken to investigate the effect of wall frictional drag reduction realized in turbulent boundary layers by injection of bubbles. Introducing the state-of-the-arts technique for measurement of complex high-speed two-phase turbulent flow, the fluid mechanics of drag reduction was explored. Moreover, such accumulated knowledges were utilized for actual design of the drag reduction control system applicable to large marine vessels, and its performance was demonstrated. These results were published in many international journals, indicating our presence of the research and development of this field.
• Development of non-invasive inline rheometry for promoting smart factory

  JST：2019年度A-STEP機能検証フェーズ試験研究タイプ

  Date (from‐to) : 2019/09 -2020/08 

  Author : Yuji Tasaka
• Inquisition of edge of chaos by perturbations acompanying hair-pin vortices

  文部科学省：科学研究費補助金（基盤研究（B)）

  Date (from‐to) : 2016/04 -2019/03 

  Author : Yuji Tasaka
• 乱流パフの個性とその生存率における出生の影響

  文部科学省：国際共同研究加速基金（国際共同研究強化）

  Date (from‐to) : 2016/04 -2018/03 

  Author : 田坂裕司
• Pressure field measurement system for 3D flows around rotating wind turbines

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2015/04 -2017/03 

  Author : Murai Yuichi

   

  Wind power now speads at a pace of ten folds a decade, and experiences various problems which has not been pointed out before such as lack of power estimated, blade damage with sudden unstable airflows, and flow noises claimed by residents. All of them associate to pressure field of flow. Particle image velocimetry has been contributing to experimental fluid dynamics though, it hardly produces problem-solving of the issue above. This is because PIV does not measure pressure field directly despite to its rich information of velocity vector field. In this project, we have developed several numerical and experimental systems that can measure multi-dimensional pressure field as a function of time, to improve the pace of development in trial-and-error designs of various wind turbines.
• Smart control of gas-liquid two-phase turbulent boundary layer

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2012/04 -2017/03 

  Author : Murai Yuichi

   

  After great dissaster of east Japan 2011, our human kind is tasked to realize high energy safety and production in improved efficiency upon needs of sustainable society. Marine technoligy is one of such concerns, to which we develop turbulent frictional drag reduction method feasible to marine vessels. In this project, we have established three kinds of new techniques that convert unstable bubbly two-phase flow to controled state to save energy consumption of large ships through multiple laboratory scaled fundamental experiments to find out hidden science in bubbly turbulent boundary layer at high Reynolds numbers. We have eventually suceeded in 15% energy saving for four kinds of marine vessels demonsrated by sea-trial as well.
• Rhythm of magma transport in deformable porous media

  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.
• New mechanism for geomagnetic polarity reversals induced by flow reversals

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2012/04 -2016/03 

  Author : YANAGISAWA Takatoshi, TASAKA Yuji, KAGEYAMA Akira, SAKURABA Ataru, MIYAGOSHI Takehiro, SUMITA Ikuro, HAMANO Yozo

   

  We explored magnetoconvection and rotating convection by means of laboratory experiments and numerical simulations, to elucidate the mechanism that induces geomagnetic polarity reversals. We established a regime diagram of convection in a liquid metal under the influence of imposed horizontal magnetic field. The searched space is summarized by the relation between buoyancy and magnetic force, in which a regime exists that reversals of flow direction repeat intermittently. We found that the key mechanism for flow reversals is an occurrence of large-scale circulation in a horizontal plane. We also performed numerical simulations of dynamos in a rotating spherical shell, and clarified the relation between polarity reversals and transitions of convection flow.
• Characteristics of turbulent puffs and its dependence of generation scheme

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2013 -2015 

  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.
• Landmark design for determination of future type wind turbines

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2011 -2012 

  Author : MURAI Yuichi, TASAKA Yuji

   

  Upon the generation that the use of wind energy grows up ten fold in every decade, a two-year project has been carried out in order to judge the vision of design method that will persist in future. The project is planed based on finding essential problems in current age to choose problems that we encounter in the next age. Five kinds of themes are selected and studied through wind tunnel experiments, numerical simulations, and on-site investigation at local wind farms.
• Improvement of efficiency on frictional drag reduction by repetitive bubble injection

  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.
• Determination of the energy dissipation in the Geodynamo

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2009 -2011 

  Author : HAMANO Yozo, KAGEYAMA Akira, MIYAGOSHI Takehiro, YANAGISAWA Takatoshi, TASAKA Yuji, SUMITA Ikuro, SAKURABA Ataru, TAKEDA Yasushi

   

  Laboratory experiments on the turbulent thermal convection of a liquid metal under ambient magnetic fields with various intensities were carried out. Consulting with the observed variations of the geomagnetic field and the results of geodynamo simulations, we tried to infer the turbulent state and the energy dissipation in the Earth's core. In the experiments, we found spontaneous reversals of the flow patterns of thermal convections within a certain range of the intensity of the magnetic fields and the Rayleigh numbers, which might be important to understand the origin of the geomagnetic field reversals.
• Sweeping the unexplained factors in microbubble fluids by complex viscosity analysis

  Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research

  Date (from‐to) : 2009 -2011 

  Author : MURAI Yuichi, TASAKA Yuji, KITAGAWA Atsuhide, ISHIKAWA Masaaki, TAKEDA Yasushi

   

  Rheological characteristics of microbubble mixture are investigated experimentally from laminar to turbulent states to obtain following findings : Non-equilibrium deformation of bubbles in oscillatory shear provides effective viscosity higher than 10 times as that of equilibrium deformation. In transition mode to turbulence, flow modulation is suppressed with microbubble, proving the fundamental function of transition delay. Reduction in turbulent intensity, promotion of heat transfer, and emergence of new type boundary layer structure with clustering of bubbles are also found in turbulent states.
• Pioneering Study of PIV Technology for Large Scale Airflows

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(B))

  Date (from‐to) : 2006 -2008 

  Author : Yasushi TAKEDA, Yuichi MURAI, Yuji TASAKA

   

  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.
• Turbulence in the Earth's outer core

  Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(A))

  Date (from‐to) : 2006 -2008 

  Author : Yozo HAMANO, Yasushi TAKEDA, Ikuro SUMITA, Ataru SAKURABA, Takatoshi YANAGISAWA, Hiroaki TOH, Yuji TASAKA, 吉原 新

   

  本研究では、磁場変動の観測、室内実験、及び数値シミュレーションを相互に連携して進めた。磁場変動の観測では、北西太平洋海底の2 観測点での長期計測を実現し良質なデータを得た。室内実験では、液体金属の熱対流に水平及び垂直方向の磁場を印加し、磁場強度の増加による対流の様相並びに乱流スペクトルの変化をとらえることに成功した。数値シミュレーションでは、球殻熱対流ダイナモを数多くの設定で実現し詳細な解析を行った。これらを総合することで、地球流体核の乱流状態に関する示唆が得られた。
• 液-液体金属二層流れの振る舞いを知るための実験研究

  文部科学省：科学研究費補助金(若手研究(B))

  Date (from‐to) : 2006 -2007 

  Author : 田坂 裕司

   

  液-液体金属二層流れは,地球物理学におけるコアーマントル境界の問題からシリコン単結晶生産における品質管理まで,幅広い分野に関係する現象である.それらの問題を解決するため主に以下に示す4つのテーマで事件研究を遂行し,それぞれ結果を得た.(1)液体金属内熱対流と磁場による制御 複数線での超音波流速分布計測(UVP)により、液体ガリウム中に形成される対流セルの3次元運動を調べた.また、得られた速度分布変動と、サーミスタによる温度計測結果の周波数解析を行い、時間変動のスケールを明らかにした.さらに,ヘルムホルツコイルにより形成された一様磁場による制御に取り組み,対流中に現れる短い時間スケールの変動を抑制すると共に,対流セルの上記のサイズを変化させることに成功した.(2)液体金属のスピンアップにおける過渡的な流れを用いた実効粘性と透磁率の測定 一様磁場中に置かれた円筒に液体金属を満たし回転させ、スピンアップ時の過渡的な変動磁場と速度分布変化を計測した.この結果から液体金属の磁場中における実効粘性と透磁率を求めた.計測はおもにフランス、非平衡現象研究所(IRPHE)で行った.(3)自由界面を有する回転流れの表面形状Switching現象 この現象に関して,流れを理解するための実験研究を行い,それを制御するための知見を得た.また液体金属は粘性の効果が小さく乱れやすいが,表面張力が大きく界面...

Industrial Property Rights

• 特許7412786: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  

  田坂裕司, 芳田泰基, 村井祐一
• 特願2021-029219:超音波物性測定装置  2021年/02/25

  田坂裕司, 芳田泰基, 大家広平  国立大学法人北海道大学
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• 特許5208124:Ultrasonic multiphase flowmeter, ultrasonic multiphase flow rate measurement program, and multiphase flow rate measurement method using ultrasonic wave    2013/03/01

  Y.Takeda, Y.Murai, Y.Tasaka