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Last Updated :2024/10/15

研究者情報

マスター

アカウント（マスター）

  • 氏名

    村井　祐一(ムライ　ユウイチ), ムライ　ユウイチ

所属（マスター）

  • 工学研究院　機械・宇宙航空工学部門　熱流体システム

所属（マスター）

  • 工学研究院　機械・宇宙航空工学部門　熱流体システム

独自項目

syllabus

  • 2021, 流体工学特論, Advanced Fluid Engineering, 修士課程, 工学院
  • 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, Fluid engineering, Theory of thermal-fluid mechanics, Computational fluid mechanics, Flow measurement & visualization, Food Science
  • 2021, エネルギー技術・政策特論, Overview of Energy Technology and Policy, 修士課程, 工学院, Energy, Renewable Energy, Environment, Economy, Policy
  • 2021, 大学院共通授業科目（一般科目）：自然科学・応用科学, Inter-Graduate School Classes(General Subject):Natural and Applied Sciences, 修士課程, 大学院共通科目, Energy, Renewable Energy, Environment, Economy, Policy
  • 2021, 原子力・エネルギーシステム特論, Nuclear and Various Energy Systems, 修士課程, 工学院, 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • 2021, 流体エネルギー工学特論, Fluid Power Systems, 修士課程, 工学院, 流体機械, 風力, 水力発電, 省エネ技術, 自然エネルギー, 環境流体力学, 混相流
  • 2021, 流体工学特論, Advanced Fluid Engineering, 博士後期課程, 工学院
  • 2021, エネルギー技術・政策特論, Overview of Energy Technology and Policy, 博士後期課程, 工学院, Energy, Renewable Energy, Environment, Economy, Policy
  • 2021, 原子力・エネルギーシステム特論, Nuclear and Various Energy Systems, 博士後期課程, 工学院, 原子力、原子力安全、核燃料サイクル、核不拡散、核融合、再生可能エネルギー、次世代自動車
  • 2021, 流体エネルギー工学特論, Fluid Power Systems, 博士後期課程, 工学院, 流体機械, 風力, 水力発電, 省エネ技術, 自然エネルギー, 環境流体力学, 混相流
  • 2021, 工業英語演習, Exercise on Technical English, 学士課程, 工学部, 工業英語、英文読解、英作文、英会話、プレゼンテーション、討論
  • 2021, 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ), Freshman Seminar, 学士課程, 全学教育, 地球環境のための科学技術（エンジン、風力，水力） 原子力の役割（システム、安全、放射性廃棄物）
  • 2021, エネルギー工学概論, Introduction to Energy Engineering, 学士課程, 工学部, 地球環境、火力発電、原子力発電、再生可能エネルギー、省エネルギー
  • 2021, 流体力学Ⅰ, Fluid Dynamics Ⅰ, 学士課程, 工学部, 流体力学，検査体積，保存法則，連続の式，運動量，エネルギー，ベルヌーイの定理，渦運動，流線，ポテンシャル流れ，流れ関数

researchmap

プロフィール情報

学位

  • 博士（工学）（1996年07月 東京大学）

プロフィール情報

  • プロフィール

    革新的省エネルギー技術の開発，自然エネルギーの難題解決，それらを実現する新しい流体計測技術の開発に，日々の時間を使っています．船舶，食品，風力，燃料，地球などが研究室のキーワードです．レーザーや超音波による独自開発の計測ツールを拡張しながら，物理の発見と技術の提案をしています．

  • 姓

    村井, ムライ

  • 名

    祐一, ユウイチ

  • ID各種

    200901065173477867

対象リソース

業績リスト

研究キーワード

  • 流体計測   自然エネルギー   風車   気泡   抵抗低減   船舶   可視化   PIV   超音波   マイクロバブル   流体工学   風力発電   混相流   鳥   省エネルギー   画像計測   流体力学   Image analysis   Fluid Dynamics   

研究分野

  • 社会基盤（土木・建築・防災） / 防災工学
  • フロンティア（航空・船舶） / 船舶海洋工学
  • ものづくり技術（機械・電気電子・化学工学） / 計測工学
  • ものづくり技術（機械・電気電子・化学工学） / 流体工学

経歴

  • 2010年04月 - 現在 北海道大学大学院工学研究院 教授
  • 2005年04月 - 2010年03月 北海道大学大学院工学研究科 准教授
  • 2003年04月 - 2005年03月 北海道大学大学院工学研究科 助教授
  • 2001年03月 - 2003年03月 ロンドン大学インペリアルカレッジ 客員研究員
  • 2000年06月 - 2001年02月 福井大学工学部 助教授
  • 1995年04月 - 2000年05月 福井大学工学部 助手
  • 1993年04月 - 1995年03月 東京大学大学院工学系研究科 日本学術振興会特別研究員

学歴

  •         - 1996年07月   博士（工学）（東京大学、論博）
  •         - 1995年03月   東京大学   大学院工学系研究科   機械工学専攻 博士課程中退
  •         - 1995年03月   東京大学   大学院工学系研究科   機械工学専攻 修士課程修了
  •         - 1991年03月   金沢大学   工学部   機械システム工学科卒 卒業
  •         - 1989年03月   国立石川工業高等専門学校   機械工学科 卒業

委員歴

  • 2023年08月 - 現在   日本混相流学会   会長
  • 2022年09月 - 現在   日本学術会議   連携委員
  • 2022年04月 - 現在   日本機械学会   理事，フェロー
  • 2022年01月 - 現在   日本流体力学会   フェロー
  • 2020年07月 - 現在   科学技術振興機構(JST)   CRDS アドバイゾリ委員
  • 2020年07月 - 現在   PIV国際会議   Scientific Committee
  • 2020年06月 - 現在   超音波ドップラー国際会議   ボードメンバー
  • 2018年07月 - 現在   レーザー流体国際会議   ボードメンバー
  • 2018年01月 - 現在   Experiments in Fluids   Associate Editor
  • 2016年04月 - 現在   日本機械学会   イノベーションセンター研究分科会主査
  • 2022年08月 - 2023年08月   可視化情報学会   可視化情報シンポジウム実行委員長
  • 2016年06月 - 2023年04月   国際混相流会議   ICMFガバニングボード議長
  • 2019年08月 - 2022年07月   日本混相流学会   理事 国際部会長
  • 2017年01月 - 2022年05月   日米二相流専門家会議   実行委員長
  • 2021年04月 - 2022年03月   日本機械学会   代表会員
  • 2016年01月 - 2021年01月   Nuclear Eng. Design   エディター
  • 2018年10月 - 2020年09月   日本学術会議   機械工学将来展望委員会委員
  • 2016年08月 - 2020年07月   日本混相流学会   混相流論文審査委員長
  • 2014年04月 - 2020年03月   日本機械学会   J. Fluid Sci. Tech. エディター
  • 2016年04月 - 2019年03月   日本機械学会   Mech Eng Lett. エディター
  • 2012年10月 - 2017年12月   Experiments in Fluids   編集アドバイゾリボード
  • 2014年06月 - 2017年05月   日本機械学会   北海道支部流体工学研究会委員長
  • 2015年01月 - 2017年01月   混相流計測国際会議   議長
  • 2012年06月 - 2016年07月   日本混相流学会   理事
  • 2014年01月 - 2015年01月   日本混相流学会   混相流シンポジウム実行委員長
  • 2010年07月 - 2013年06月   可視化情報学会   代議員
  • 2011年04月 - 2013年03月   日本流体力学会   代議員
  • 2008年 - 2011年   Measurement Sci. Tech.   エディター
  • 2006年08月 - 2009年03月   日本ガス協会   国プロ特別評価委員
  • 2004年04月 - 2006年03月   日本機械学会   北海道支部流体工学懇話会幹事
  • 2005年03月 - 2006年02月   日本機械学会   北海道支部商議員幹事
  • 2003年07月 - 2005年06月   可視化情報学会   PIV国内委員会幹事
  • 2004年04月 - 2005年03月   日本機械学会   学会誌編集委員
  • 2003年04月 - 2005年03月   日本機械学会   流体工学部門広報委員
  • 2004年03月 - 2005年02月   日本機械学会   北海道支部学生会顧問
  • 2000年12月 - 2004年09月   日本機械学会   年次大会現地実行委員会総務
  • 1998年07月 - 2000年06月   可視化情報学会   PIV標準化委員
  • 1996年04月 - 2000年03月   日本混相流学会   広報委員

受賞

  • 2023年03月 日本機械学会北海道支部 技術賞
     国際マラソン用に対応した開口型ロードコーンの耐風技術の開発 
    受賞者: 村井祐一;田坂裕司;朴 炫珍;芦田俊樹;永井繁行
  • 2022年08月 日本混相流学会 日本混相流学会・貢献賞
     「学会の国際交流への貢献」 
    受賞者: 村井祐一
  • 2020年08月 日本混相流学会 日本混相流学会・論文賞
     「気液二相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
  • 2020年07月 可視化情報学会 可視化情報学会・論文賞
     「回転レーリーベナール対流の渦温度場可視化」 
    受賞者: 能登大輔;田坂裕司;柳澤孝寿;朴炫珍;村井祐一
  • 2018年07月 可視化情報学会 可視化情報学会・技術賞
     「超音波による食品物性可視化」 
    受賞者: 芳田泰基;田坂裕司;朴炫珍;村井祐一
  • 2017年04月 日本機械学会 日本機械学会・技術賞
     「二相流境界層のスマート制御」 
    受賞者: 村井祐一;熊谷一郎;田坂裕司;朴 炫珍;高橋義明
  • 2017年02月 英国物理学会IOP 英国物理学会・Outstanding Reviewer's Award
     
    受賞者: 村井祐一
  • 2016年03月 日本機械学会 日本機械学会北海道支部・研究技術賞
     「風車バードストライク」 
    受賞者: 村井祐一;田坂裕司;大石義彦;武田 靖;粂野博行
  • 2015年06月 可視化情報学会 可視化情報学会・技術賞
     「文学の流体力学的可視化」 
    受賞者: 山田美幸;村井祐一;熊谷一郎
  • 2014年07月 日本混相流学会 日本混相流学会・技術賞
     「混相流の超音波計測」 
    受賞者: 村井祐一;田坂裕司;武田 靖
  • 2014年07月 可視化情報学会 可視化情報学会・論文賞
     「粘弾性流体の可視化」 
    受賞者: 白鳥貴久;田坂裕司;村井祐一;武田 靖
  • 2012年07月 日本混相流学会 日本混相流学会・論文賞
     「水中翼気泡発生装置」 
    受賞者: 熊谷一郎;田坂裕司;村井祐一
  • 2011年10月 日本機械学会 日本機械学会流体工学部門・フロンティア賞
     「二相流体工学技術」 
    受賞者: 村井 祐一
  • 2010年11月 日本ガス協会 日本ガス協会・論文賞
     「パイプライン流量計」 
    受賞者: 竹内智朗;村井祐一
  • 2010年08月 日本混相流学会 日本混相流学会・論文賞
     「気泡流のレイノルズ応力」 
    受賞者: 大石義彦;村井祐一;田坂裕司;武田 靖
  • 2009年07月 可視化情報学会 可視化情報学会・最優秀講演賞
     「バードストライク」 
    受賞者: 村井祐一;田坂裕司;武田 靖
  • 2009年07月 可視化情報学会 可視化情報学会・20周年記念功労賞
     「混相流OS」 
    受賞者: 村井祐一
  • 2009年03月 北海道大学 北海道大学・エクセレントティーチャーズ
     「応用数学」 
    受賞者: 村井 祐一
  • 2008年07月 可視化情報学会 可視化情報学会・技術賞
     「宇宙用ギアポンプ」 
    受賞者: 村井祐一;上埜安隆;大岩浩司;宮城直樹;山本富士夫;伊東哲也
  • 2007年10月 油空圧機器技術振興財団 油空圧機器技術振興財団・論文賞
     「マイクロポンプ」 
    受賞者: 宮城直樹;村井祐一;宮﨑孝司;山本富士夫
  • 2007年04月 文部科学省 文部科学省・文部科学大臣賞 若手科学者賞
     「流体エネルギー制御システム技術」 
    受賞者: 村井祐一
  • 2005年10月 日本機械学会 日本機械学会流体工学部門・貢献賞
     「日韓熱流体会議の運営」 
    受賞者: 村井 祐一
  • 2005年04月 日本機械学会 日本機械学会・論文賞
     「気泡間相互作用」 
    受賞者: 北川石英;杉山和靖;笹木俊男;村井祐一
  • 2003年04月 日本機械学会 日本機械学会・教育賞
     「市民機械工学講座」 
    受賞者: 村井祐一;伊藤隆基;永井二郎;本田知己;石川拓司
  • 2000年07月 日本混相流学会 日本混相流学会・貢献賞
     「ホームページ構築」 
    受賞者: 村井 祐一
  • 1998年07月 可視化情報学会 可視化情報学会・研究奨励賞
     「二相流のステレオ可視化」 
    受賞者: 村井 祐一
  • 1998年04月 日本機械学会 日本機械学会・論文賞
     「気泡流の数値解析法」 
    受賞者: 松本洋一郎;村井祐一
  • 1989年03月 日本機械学会 日本機械学会・畠山賞
     
    受賞者: 村井 祐一

論文

  • Wenqing Zheng, Yuji Tasaka, Kohei Ohie, Yuichi Murai
    Measurement Science and Technology 2024年09月10日 
    Abstract We propose a method for estimating volume fraction of emulsions based on ultrasonic velocity profiling viscometry and validate its feasibility through a series of experiments. The experiments involve emulsions composed of silicone oil as continuous phase and tap water with volume fractions ranging from 10vol% to 30vol%. We introduce the viscosity model for this emulsion to establish the mathematical relationship between volume fraction and viscosity. Subsequently, we calibrate this relationship using ultrasonic spinning rheometry (USR). The identified equation is then applied in estimating the inline volume fraction using ultrasonic velocity profiling combined with pressure drop measurement. The key idea is that by measuring the viscosity in a pipeline the volume fraction is then indirectly estimated employing the identified equation. Through the collection and analysis of experimental data, we confirmed that the USR can capture the characteristics of the emulsion viscosity accurately. Moreover, we found that this method demonstrates applicability and accuracy in measuring volume fractions of emulsions. The results indicate that the mean relative error for this estimation is 24.06% at a volume fraction of 10vol%, and 4.78% at a volume fraction of 30vol%.
  • Sotaro Masanobu, Satoru Takano, Marcio Yamamoto, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    Journal of Offshore Mechanics and Arctic Engineering 1 - 40 2024年07月16日 
    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.
  • 村井 祐一, 大友 衆示, 大須賀 侑, 山口 哲太
    日本機械学会論文集 90 933 2024年05月 [査読有り][通常論文]
  • Yasufumi HORIMOTO, Itsuki MORI, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI
    Journal of Fluid Science and Technology 19 2 JFST0013 - JFST0013 2024年05月 [査読有り][通常論文]
  • Yoshimichi Ono, Ryosuke Sayama, Yuichi Murai, Hyun Jin Park, Yuji Tasaka
    Wind Energy 27 483 - 499 2024年04月17日 [査読有り][通常論文]
     
    Abstract The use of a turbo‐sail airfoil to improve the power generation of a Darrieus wind turbine was examined. The turbo‐sail airfoil comprises a symmetric blade from which a high‐speed tangential jet is produced to suppress flow separation. For a steady angle of attack, we experimentally confirmed an anti‐stall function of the airfoil at an angle of attack up to and exceeding 30°. Considering the case of the rotation of a single blade of a Darrieus wind turbine, the flow field was replaced with a non‐separated stream around the airfoil particularly even at a tip‐speed ratio lower than 3. The pressure field and local lift‐to‐drag ratio measured by particle image velocimetry quantitatively supported the expected anti‐stall function. Improvements in the torque and power coefficient were estimated from measurements considering the external power consumed in supplying the jet.
  • Yuichi Murai, Takahiro Umemura, Hyun Jin Park, Yasufumi Horimoto, Yuji Tasaka
    Journal of Fluids and Structures 127 104105  2024年04月 [査読有り][通常論文]
  • K. Ohie, Y. Tasaka, Y. Murai
    Journal of Fluid Mechanics 983 A39 2024年03月25日
  • Shūji Ōtomo, Yuji Tasaka, Petr Denissenko, Yuichi Murai
    Physics of Fluids 36 027104 2024年02月01日 [査読有り][通常論文]
     
    With an increasing demand for small energy generation in urban areas, small-scale Savonius wind turbines are growing their share rapidly. In such an environment, Savonius turbines are exposed to low mean velocity with highly turbulent flows made by complex geographies. Here, we report the flow-induced rotation of a Savonius turbine in a highly turbulent flow (18% turbulence intensity). The high turbulence is realized by using the far-field of an open-jet. Compared to low turbulence inflow (1% turbulence intensity), the turbine rotates 4% faster in high turbulence since the torque/power increases with turbulence intensity. The wake measurement by hot-wire anemometry and particle image velocimetry reveals the suppression of vortex shedding in high turbulence. In addition, a newly developed semi-empirical low-order model, which can include the effect of turbulence intensity and integral length scale, also confirms high turbulence intensity contributes to the rotation of the turbine. These results will boost more installation of small Savonius turbines in urban areas in the future.
  • Yoshihiko Oishi, Sho Onuma, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hideki Kawai
    Flow Measurement and Instrumentation 96 102546 - 102546 2024年02月 [査読有り][通常論文]
  • Hyun Jin Park, Tatsuya Hamada, Chiharu Kawakita, Yuichi Murai
    Ocean Engineering 289 116248 - 116248 2023年12月
  • Taiji Tanaka, Ryo Aoki, Yuichi Murai
    Experiments in Fluids 64 147 2023年08月12日 [査読有り][通常論文]
  • Sotaro Masanobu, Satoru Takano, Marcio Yamamoto, Yuichi Murai, Yuji Tasaka, Hyun Jin Park
    Volume 4: Ocean Space Utilization 2023年06月11日 [査読有り][通常論文]
     
    Abstract For subsea mining, it is important to predict the pressure loss in oscillating pipes with pulsating slurry flow for the safe and reliable operation of ore lifting. The configuration of pipe is expected to have not only vertical but also inclined parts. In the present paper, the authors focused on the pulsating internal slurry flow in static inclined pipes and derived the mathematical model to predict the pressure loss in such conditions. The slurry transport experiment was carried out to investigate the effects of pulsating slurry flow on the pressure loss in inclined pipes. In the experiment, the data related to slurry flow was measured by the differential pressure gauges, the electromagnetic flowmeter and the ultrasound monitoring. The model derived was validated by a comparison with measured data. The measured pressure loss has an outstanding component with pulsating period of water flow with relatively small higher order harmonic components. Although the prediction model derived in the present study has a tendency to overestimate the pressure loss for larger inclination angles, the calculated pressure loss is within the acceptable range given the simplicity of the model.
  • Hanrui Zhang, Feng Dong, Yuichi Murai, Chao Tan
    Flow Measurement and Instrumentation 90 102326 - 102326 2023年04月 [査読有り][通常論文]
  • Daisuke Noto, Yuji Tasaka, Yuichi Murai
    Experiments in Fluids 64 92  2023年04月 [査読無し][招待有り]
  • Dongik Yoon, Takumi Hayashi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Satoru Takano, Sotaro Masanobu
    Flow Measurement and Instrumentation 91 102357 - 102357 2023年03月 [査読有り][通常論文]
  • Taiji Tanaka, Yoshihiko Oishi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Chiharu Kawakita
    Ocean Engineering 272 113807 - 113807 2023年03月 [査読有り][通常論文]
  • Yuichi Murai, Masaaki Ishikawa
    Nuclear Technology 209 1 - 14 2023年02月24日 [査読有り][通常論文]
  • Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    Industrial & Engineering Chemistry Research 61 49 18157 - 18164 2022年12月14日
  • Behaviors of sliding bubbles in an inclinable turbulent channel flow investigated by optoacoustic measurement
    D.Yoon, H.J.Park, Y.Tasaka, Y.Murai
    International Journal of Multiphase Flow, Vol. 158, No. 104258 (2022) 2022年10月 [査読有り][通常論文]
  • A.Kitagawa, M.Ota, T.Watamura, T.Tonooka, Y.Murai
    Chemical Engineering Science, Vol. 264, No. 118163 (2022) 264 118163 - 118163 2022年10月 [査読有り][通常論文]
  • Yuichi MURAI, Yuji TASAKA, Hyun Jin PARK, Satoru TAKANO, Sotaro MASANOBU
    JAPANESE JOURNAL OF MULTIPHASE FLOW 36 3 329 - 335 2022年09月15日
  • H.J.Park, D.Yoon, S.Akasaka, Y.Tasaka, Y.Murai
    Experiments in Fluids, Vol. 63, No. 130 (2022) 63 8 2022年08月 [査読有り][通常論文]
  • Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Masako Sugihara-Seki, Yuichi Murai
    Experiments in Fluids 63 8 2022年08月
  • Yuichi Murai, Takumi Hayashi, Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Satoru Takano, Sotaro Masanobu
    Experiments in Fluids 63 8 2022年08月
  • Evaluation of time-dependent rheological property in the coagulation of skimmed milk by ultrasonic velocity profiler
    A.Takano, K.Ohie, Y.Horimoto, Y.Tasaka, Y.Murai
    Transaction of JSME, Vol. 88, No. 911, pp.1-13(2022) 2022年07月 [査読有り][通常論文]
  • Sotaro Masanobu, Marcio Yamamoto, Satoru Takano, Yuichi Murai
    Proceedings of the ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering (OMAE2022) 4 OMAE2022-79597  2022年06月 [査読有り]
     
    Abstract For design and operation of subsea mining system, it is important to predict pressure loss due to the hydraulic transport of solid particles in the flexible jumper which connects the mining tool to the vertical lifting pipe via subsea slurry pump. The configurations of jumper would change according to the motions of the mining tool and the slurry pump, which may be easier to cause the pipe blockage than the vertical pipe. In the present paper, we investigated the effects of jumper configuration on the pressure loss. We assumed the 100 m long flexible jumper of which outer and inner diameters are 0.254 m and 0.200 m, respectively. PMS ore, of which density and diameter are 3,440 kg/m3 and 0.03 m respectively, were assumed as the solid particles. We varied the slurry transport conditions such as slurry concentration and slurry velocity under the condition of a constant production rate of 5,000 t/day. The effects of jumper configuration on internal slurry flow were studied from the viewpoint of pressure loss and specific energy consumption. The allowable slurry velocity in jumper system was also investigated considering pipe inclination by referring to the past literature. Finally, the most desirable operational slurry flow condition was discussed for the jumper system studied.
  • Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    Physics of Fluids 34 5 053301 - 053301 2022年05月 
    The behavior of bubbles traveling in the proximity of a tilted wall is studied experimentally to understand the fundamental sliding motion of bubbles inside turbulent boundary layers along an inclined wall. The qualitative visualization of sliding bubbles confirms the contribution of bubble buoyancy on the sliding motion for negative and positive inclinations of the channel. An opto-acoustic combined measurement technique is adopted to explore the sliding motion. Liquid velocity profiles in the bubbly flow and the distance between the wall and bottom of the bubble are obtained using the ultrasound pulsed Doppler method, while the bubble diameters and velocities are obtained from particle-tracking type image processing. The combined measurements reveal that the velocity of bubbles decreases under the negative slope condition and increases under the positive slope condition due to opposite buoyancy effects. In addition, the distance between the wall and bottom of the bubble increases with an increase in negative inclination. The lift coefficient is derived from the measured variables using a force–balance equation among the buoyancy, lift, and surface tension. Finally, we propose modeling equations for the lift coefficient expressed in terms of the Reynolds, Weber, and Bond numbers, which apply to the bubbles inside boundary layers.
  • Taiji Tanaka, Yoshihiko Oishi, Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Chiharu Kawakita
    Ocean Engineering 252 111224 - 111224 2022年05月
  • Dongik Yoon, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    International Journal of Multiphase Flow 149 103995 - 103995 2022年04月
  • Taiki Yoshida, Yuji Tasaka, Kohei Ohie, Yuichi Murai
    Nihon Reoroji Gakkaishi 50 1 3 - 7 2022年02月15日
  • Kohei Ohie, Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    EXPERIMENTS IN FLUIDS 63 2 2022年02月 
    We propose a practical map representation termed rheology mapping for comprehensively evaluating the dependence of viscoelasticity on applied shear deformation and shear timescale represented by oscillation frequency, utilizing ultrasonic spinning rheometry, which has excellent applicability to a wide variety of polymer solutions. The rheology mapping was applied to two typical kinds of polymer solutions. One is carboxymethyl cellulose (CMC) aqueous solution, a well-known viscous and shear thinning fluid. The other is polyacrylamide (PAM) aqueous solution generally considered as a viscoelastic fluid while its viscoelasticity is difficult to be evaluated by a standard torque-type rheometer. The rheology mapping for the solutions showed notable rheological properties. The viscoelasticity of both the CMC and PAM solutions vary widely from elastic to viscous, depending on the applied shear rate, strain, and oscillation frequency. The mapping also revealed the clear dependence of the viscosity of the solutions: the CMC solutions on the shear rate and the PAM solutions on the shear strain. These results provide quantitative support of findings in other reports associating these macroscopic properties with the microscopic dynamics of polymer coils.[GRAPHICS].
  • Taiki Yoshida, Yuji Tasaka, Peter Fischer, Yuichi Murai
    Applied Clay Science 217 106395 - 106395 2022年02月
  • H.J. Park, Y. Tasaka, Y. Murai
    International Journal of Multiphase Flow 2022年01月 [査読有り]
  • Taiji TANAKA, Yoshihiko OISHI, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI, Chiharu KAWAKITA
    Transactions of the JSME (in Japanese) 2022年
  • Y. Murai, T. Yumoto, H.J. Park, Y. Tasaka
    Experiments in Fluids 62 231  2021年11月 [査読有り]
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    Experiments in Fluids 62 9 2021年09月01日 
    We experimentally investigate air bubbles sticking to a hydrophobic strip on a hydrophilic ceiling in a horizontal turbulent channel flow. Simultaneous measurements of wall-sticking bubbles are conducted in two perpendicular planes using two cameras to estimate their size and contact angles and hence evaluate the drag coefficient. In a range of the bubble Reynolds number, Reb (250 ≤ Reb ≤ 1480) and a range of the Weber number, We (0.7 ≤ We ≤ 6.5), the drag coefficient for a single, deformable bubble stuck on the surface is almost independent of Reb and We and tends to be slightly higher than that of a non-deformable bubble fixed on a wall in linear shear flow. We also investigate the entrapment and cross-flow transport of air bubbles using an oriented hydrophobic strip on a hydrophilic surface. Bubbles creeping along the hydrophobic strip become trapped when reaching its edge where the downstream contact angle changes. When the strip edge is inclined relative to the flow, bubbles creep along the hydrophobic–hydrophilic boundary and thus move in the cross-stream direction. The cross-stream transport of the bubbles strongly depends on the channel Reynolds number and the angle between the hydrophobic strip and the stream. Graphic abstract: [Figure not available: see fulltext.]
  • マイクロバブルによる乱流摩擦抵抗低減
    村井祐一
    ながれ, Vol. 40, pp.252-259 (2021) 40 252 - 259 2021年09月 [査読有り][招待有り]
  • Ultrasonic Doppler technique for applications in multiphase flow: a review
    C.Tan, Y.Murai, W.Liu, Y.Tasaka, F.Dong, Y.Takeda
    International Journal of Multiphase Flow, Vol. 144, No. 103811 (2021) 144 2021年09月 [査読有り][招待有り]
  • T.Tanaka, Y.Oishi, H.J.Park, Y.Tasaka, Y.Murai, C.Kawakita
    Ocean Engineering, Vol. 239, No. 109909 (2021) 239 109909 - 109909 2021年09月 [査読有り][通常論文]
  • S.Kim, N.Oshima, H.J.Park, Y.Murai
    International Journal of Multiphase Flow, Vol.145, No. 103838 (2021) 145 103838 - 103838 2021年09月 [査読有り][通常論文]
  • Ultrasonic velocity profiler applied to explore viscosity-pressure fields and their coupling in ineastic shear thinning vortex streets
    N.Tiwari, Y.Murai
    Experiments in Fluids , Vol. 62, No. 185 (2021) 185 2021年08月 [査読有り][通常論文]
  • Bifurcation analysis of bubble-induced convection in a horizontal liquid layer: role of forces on bubbles
    K.Nakamura, H.Yoshikawa, Y.Tasaka, Y.Murai
    Journal of Fluid Mechanics, Vol. 923, R4 (2021) 923 2021年08月 [査読有り]
  • Non-intrusive in-line rheometry using ultrasonic velocity profiling
    Y.Tasaka, T.Yoshida, Y.Murai
    Industrial and Engineering Chemistry Research, Vol. 60, pp.11535-11543 (2021) 60 11535 - 11543 2021年07月 [査読有り][通常論文]
  • In situ color-to-depth caliburation: toward practical three-dimensional color particle tracking velocimetry
    D.Noto, Y.Tasaka, Y.Murai
    Experiments in Fluids, Vol. 62, No. 131 (2021) 2021年05月 [査読有り][通常論文]
  • Coupling structures of two-layer natural convection in a cylindrical vessel investigated by simultaneous two-layer visualization
    D.Noto, Y.Tasaka, Y.Murai
    Experimental Thermal and Fluid Science, Vol.127, No. 110394(2021 2021年04月 [査読有り]
  • Bubble fragmentation dynamics in a subsonic Venturi tube for the design of a compact microbubble generator
    Y.Murai, Y.Tasaka, Y.Oishi, P.Ern
    International Journal of Multiphase Flow, Vol. 139, No.103645(2021) 2021年03月 [査読有り]
  • H.J.Park, S.Yamagishi, S.Osuka, Y.Tasaka, Y.Murai
    Experiments in Fluids, Vol. 62, 71(2021) 62 4 2021年02月 [査読有り][通常論文]
  • 村井 祐一, 堀本 康文, 朴 炫珍, 田坂 裕司, 大石 義彦, 永田 晴紀
    北海道支部講演会講演概要集 2021.58 1312  一般社団法人 日本機械学会 2021年
  • Yuichi MURAI, Takahiro UMEMURA, Ryosuke SAYAMA, Yasufumi HORIMOTO, Hyun Jin PARK, Yuji TASAKA, Shuji OTOMO
    The Proceedings of the International Conference on Power Engineering (ICOPE) 2021.15 2021 - 0183 2021年
  • S.Nomura, J.Hitomi, Y.Murai, D.C.Giovanni, Y.Tasaka, Y.Takeda, H.J.Park, H.Sakaguchi
    International Journal of Multiphase Flow 136 2021年01月 [査読有り][通常論文]
  • N.Tiwari, Y.Tasaka, Y.Murai
    Flow Measurement and Instrumentation 77 2021年01月 [査読有り][通常論文]
  • Y.Oishi, Y.Murai, Y.Tasaka
    International Journal of Heat and Fluid Flow 86 2020年12月 [査読有り][通常論文]
  • S.Kim, N.Oshima, Y.Murai, H.Park
    Journal of Fluid Science and Technology 15 3 JFST0020 - JFST0020 2020年12月 [査読有り][通常論文]
  • Kotaro Nakamura, Harunori N. Yoshikawa, Yuji Tasaka, Yuichi Murai
    PHYSICAL REVIEW E 102 5 2020年11月 [査読有り]
     
    We investigate with a linear analysis the stability of a horizontal liquid layer subjected to injection of gas bubbles through a bottom wall. The injection is assumed uniform in space and constant in time. Injected bubbles ascend in the liquid layer due to the Archimedean buoyancy force and are ejected from the top free surface of the liquid layer. Modeling this two-phase flow system as two interpenetrating liquid and gas continua, we show that homogeneous upward gas flows become unstable at large gas fluxes. We determine the critical conditions of this homogeneous-heterogeneous regime transition and show that the critical modes are made of stationary convection rolls, either multi- or whole-layered depending on liquid viscosity, the radius of bubbles, and the thickness of liquid layer. By examining the energy transfer from base to perturbation flows, we indicate that liquid convective motion is driven by the buoyancy on heterogeneously distributed bubbles. We also reveal that the lift forces on bubbles have significant stabilizing effects by homogenizing bubble distribution close to the bottom wall.
  • Atsuhide Kitagawa, Yuriko Shiomi, Yuichi Murai, Petr Denissenko
    EXPERIMENTS IN FLUIDS 61 11 2020年10月 [査読有り]
     
    This paper presents an experimental study of horizontal channel flow with air-filled superhydrophobic grooves. Air-water interfaces in the grooves are visualized in a range of the channel Reynolds number, Re, (2000 <= Re <= 5000) while flow characteristics are evaluated using particle tracking velocimetry measurements at Re=3000 and 4000. Near the air-water interface in the superhydrophobic groove, turbulent eddies and hence the Reynolds shear stress appreciably attenuate owing to a lack of energy supply through the interface, and it takes a notable distance for the Reynolds shear stress to recover downstream of the groove. Additionally, a secondary cross-flow from the solid surface region between two grooves towards the air-water interface appears and sweeps eddies between the grooves towards the interface. The decay of turbulent eddies and the sweeping of eddies from the solid surface to the air-water interface reduce friction drag both in and immediately downstream of the grooved region.
  • Taiji Tanaka, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    OCEAN ENGINEERING 214 107850 - 107850 2020年10月 [査読有り][通常論文]
     
    Although the practical use of bubbly drag reduction for marine vessels has begun to spread, it is unclear how bubbles migrate along spatially developing turbulent boundary layers. We measured the spatiotemporal distribution of the local void fraction beneath a 4-m-long fully transparent flat-bottom model ship towed in a 100-m-long water tank with a ship speed of up to 3.00 m/s. Bubbles were injected with both constant and periodically fluctuated air flow rates into the turbulent boundary layers. With constant flow rates, 2-5-mm bubbles caused spontaneous void waves, i.e., quasiperiodic fluctuation of the local void fraction, standing at 4-8 Hz. When repetitive bubble injection, which formed artificial void waves downstream, was applied, void waves propagated at 47%-53% of the ship speed. During the propagation, we found the apparent diffusion coefficient of the void wave taking values down to 10(-4) m(2)/s and even negative values when the repetition frequency was set lower than the spontaneous frequency of void waves. This indicates that the void waves persist for several tens of meter in application to ship hulls.
  • Applicability evaluation of the stress-optic law in Newtonian fluids toward stress field measurements
    D.Noto, Y.Tasaka, J.Hitomi, Y.Murai
    Physical Review Research 2 2020年09月 [査読有り][通常論文]
  • Y.Murai, H.Sakamaki, I.Kumagai, H.Park, Y.Tasaka
    Ocean Engineering 216 2020年08月 [査読有り][通常論文]
  • Kodai Fujita, Yuji Tasaka, Takatoshi Yanagisawa, Daisuke Noto, Yuichi Murai
    JOURNAL OF VISUALIZATION 23 4 635 - 647 2020年08月 [査読有り][通常論文]
     
    To enrich the three-dimensional experimental details of vortex structures in rotating Rayleigh-Benard convection, we established a technique visualizing three-dimensional vortex structures using scanning planar particle image velocimetry. Experiments were performed at fixed Rayleigh number, Ra=1.0x10(7) to 1.0x10(8), corresponding to convective Rossby numbers from 0.1 <= Ro <= 0.5 at which gradual transition between vortical plumes and convective Taylor columns regime is observed. Stream function distributions calculated from horizontal velocity vector fields visualize the vortex structure formed in the regimes. As quantitative information extracted from the visualized structures, distances between vortices recognized on the distributions show a good agreement with that evaluated by a theory. With the accumulated planar stream function distributions and vertical velocity component calculated from the horizontal velocity vectors, the three-dimensional representations of vortices indicate that quasi-two-dimensional columnar vortices straighten in the vertical direction with increasing Ta. Graphic abstract
  • S.Tuckerm K.Igor, Y.Murai, P.Denisenko
    Applied Energy 268 2020年04月 [査読有り][通常論文]
  • 芳田 泰基, 田坂 裕司, 村井 祐一
    流体工学部門講演会講演論文集 2020 OS01 - 7 一般社団法人 日本機械学会 2020年 

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

  • Kohei OHIE, Taiki YOSHIDA, Hyun Jin PARK, Yuji TASAKA, Yuichi MURAI
    Transactions of the JSME (in Japanese) 2020年
  • Shinnosuke Obi, Koji Fukagata, Masaharu Kameda, Chisachi Kato, Yohei Morinishi, Yuichi Murai, Satoshi Watanabe, Masao Watanabe
    JOURNAL OF FLUID SCIENCE AND TECHNOLOGY 15 2 2020年
  • Toshiki ASHIDA, Yuichi MURAI, Hyun Jin PARK, Yuji TASAKA, Shigeyuki NAGAI
    Transactions of the JSME (in Japanese) 86 888 20 - 00184 2020年 [査読有り][通常論文]
  • Hyun Jin Park, Shintaro Akasaka, Yuji Tasaka, Yuichi Murai
    IEEE Sensors Journal 1 - 1 2020年 [査読有り][通常論文]
  • 芳田 泰基, 田坂 裕司, 大家 広平, 村井 祐一
    混相流 34 2 334 - 341 日本混相流学会 2020年 [査読有り][通常論文]
     

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

  • Hyun Jin Park, Daichi Saito, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 109 2019年12月 [査読有り][通常論文]
     
    Three-dimensional distribution of microbubbles dispersed in a turbulent boundary layer spatially developing along a flat plate is investigated experimentally. The aim of study is to find out visually how microbubbles interact with turbulent eddies to achieve frictional drag reduction on a wall. Setting conditions of the experiments are stream Reynolds number up to 2.3 x 10(4), microbubble volume fraction inside boundary layer less than 10(-5), and microbubble Stokes number smaller than 10(-3). Stream-wise vortices in the boundary layer were visualized by flake optics, of which spacing expands with injection of microbubbles. 3-D microbubble distributions were visualized by a color-coded volumetric illumination. The result showed preferentially accumulated microbubble clouds to low-speed streaks close to viscous sublayer and to hair-pin vortices in the buffer layer, leading to reduced diffusivity of microbubbles relative to the turbulent momentum diffusivity.
  • Tomoaki Watamura, Atsuhide Kitagawa, Yuichi Murai
    CHEMICAL ENGINEERING SCIENCE 208 115132  2019年11月 [査読有り][通常論文]
     
    To elucidate the motion of spatiotemporally developing flow structures driven by densely concentrated microbubbles, we experimentally investigated the distribution and motion of microbubbles rising along a vertical plane wall. We performed optical measurements and an ultrasonic velocity profiling to determine the distribution and motion of microbubbles. We found that the microbubbles form clouds (fluid blobs containing rich microbubbles) with a three-dimensional structure, the spatial patterns of which become more periodic in the streamwise direction than in the spanwise direction. In addition, owing to the coalescence of neighboring microbubble clouds caused by the hydrodynamic interaction between them, the separation length of the buoyant force distribution of microbubbles increases with increasing the distance from the bottom of the tank. According to the Reynolds number of the microbubbles cloud presented here, we conclude that the unsteady motion of microbubble clouds can be analogously modeled as an interacting motion of moving bodies in flow. (C) 2019 Elsevier Ltd. All rights reserved.
  • Yoshihiko Oishi, Yuichi Murai, Yuji Tasaka
    JOURNAL OF VISUALIZATION 22 5 867 - 876 2019年10月 [査読有り][通常論文]
     
    A single vortex ring subject to background rotation in the process of wall impingement has been experimentally investigated by particle tracking velocimetry (PTV). Two parameter conditions of Reynolds and Rossby numbers were chosen in addition to stationary environment as much strong and competitive Coriolis force emerges in comparison with inertia induced by vortex rings. From horizontal PTV windows set on the rotating experimental frame above the bottom wall, comprehensive influences of Coriolis force on the wall-impinging reaction are visualized as space-time three-dimensional vorticity distributions. Against natural growth of azimuthal waves due to Widnall instability, wall-impinging suppresses the waves and rather re-organizes original primary vortex because of cyclonic swirl coherently induced during impingement. This resists to turbulent collapse of vortex ring during the impingement and self-boosts own life time. We try to explain the mechanism of such an anti-decaying process in the final part, untangling the phenomenon with best read from the space-time correlations among three vorticity components.
  • Anubha Garg, Chandrima Shrivastava, Yuichi Murai, Erich J. Windhab
    PHYSICS OF FLUIDS 31 10 107109  2019年10月 [査読有り][通常論文]
     
    The complex airflow in convection ovens directly influences the heat transferred to the product placed inside, thereby affecting product quality. Characterization of related airflow profiles can provide scientific understanding for improvement of oven designs as well as important parameters for simulation of involved thermal processes. In this study, the particle-imaging velocimetry (PIV) technique was applied to visualize airflow inside a household convection oven with samples placed at three different locations on a baking tray. The oven cavity was modified for optical access, and airflow was measured at room temperature. A 30 mW green laser was used for illuminating tracer particles in a laser sheet that were generated using incense sticks. The flow patterns were captured using a high-speed camera at 1000 fps. The vorticity and turbulent kinetic energy parameters derived from velocity fields reflected adequate mixing of air inside the cavity. The computed heat transfer coefficient distribution from the boundary layer flow fields to the sample surface ranged between 2.0 and 183 W m(-2) K-1. The results showed separation of the laminar boundary layer from the object surface at angles of 85 degrees -90 degrees. The PIV-algorithms and boundary layer flow derived parameters developed in this study can be used for refined characterization of complex air or gas flows and related heat transfer characteristics in closed cavity convection ovens and the like arrangements. Published under license by AIP Publishing.
  • Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    PHYSICS OF FLUIDS 31 10 103304  2019年10月 [査読有り][通常論文]
     
    The effective viscoelasticity of non-Newtonian fluids with spherical particles has been examined by ultrasonic spinning rheometry [Yoshida et al., "Efficacy assessments in ultrasonic spinning rheometry: Linear viscoelastic analysis on non-Newtonian fluids," J. Rheol. 63, 503 (2019)]. Under unsteady shear flows, the dispersed particles make alignments in the sheared direction if the relaxation time of the fluid media is sufficiently long. The alignments modulate the effective rheological properties, and the effective viscosity does not reach the value estimated by Einstein's law; the effective elasticity increases significantly with increasing volume fraction in the bulk of the measurement volume. To establish further details of factors influencing the aligned particles under unsteady shear flows/deformations, numerical tests using a simple toy model assuming dispersed particles combined by spring forces considering yield stresses were conducted, and the model identified the importance of the relaxation process on the orientation of the particles. Finally, considering the experimental findings, local and macrorheological characteristics are strongly modulated by the particle alignment when the test fluid media have long relaxation times (or high Weissenberg numbers). Published under license by AIP Publishing.
  • Bubble clustering in a horizontal turbulent channel flow investigated via bubble-tracking velocimetry
    Y.Oishi, Y.Tohge, Y.Murai, Y.Tasaka
    International Journal of Multiphase Flow 111 2019年09月 [査読有り][通常論文]
  • Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    JOURNAL OF RHEOLOGY 63 4 503 - 517 2019年07月 [査読有り][通常論文]
     
    We have progressively developed an ultrasonic spinning rheometry (USR) that has the potential to visualize complex details of rheology, such as time-dependence, coexistence of gel and sol, effective viscosity of multiphase fluids, and other particulars. This rheometry makes it possible to overcome the main issues in conventional rheometry, originating from nonideal velocity profiles in the complex fluids. The most notable advantage of USR is the ability to perform "local" rheological evaluations from only the velocity information for a short-time period by solving the equation of motion. This benefit is provided while avoiding noise augmentations by introducing a linear viscoelastic analysis in the frequency domain. Solving the equation of motion with a rheological model equation in the frequency domain, multiple rheological parameters are quantified by minimizing the cost function. In this paper, the analysis presented by USR is verified by comparative experiments using a rheometer with the typical geometry of parallel disks. As a complementary technique for conventional rheometers, the USR efficacies are shown through rheological assessments for Newtonian, shear-thinning, and thixotropic fluids. Additionally, USR can provide instantaneous flow curves O(1 s) that lead to understanding the rheology in complex fluids with time-dependency. (C) 2019 The Society of Rheology.
  • Thermal diffusion interface inside a horizontal pipe flow compared between laminar and turbulent flow regimes
    K.Nakamura, H.J.Park, Y.Murai, T.Takeuchi
    Journal of Visualization 22 809 - 818 2019年06月 [査読有り][通常論文]
  • Neetu Tiwari, Yuji Tasaka, Yuichi Murai
    FLOW MEASUREMENT AND INSTRUMENTATION 67 23 - 32 2019年06月 [査読有り][通常論文]
     
    A novel algorithm of pressure field estimation based on ultrasound velocity profiler (UVP) is developed. The method consists of UVP measurement of velocity distribution in fluid flows and numerical analysis of the measured data using fluid dynamics equations. We introduce equation of continuity, incompressible Navier-Stokes equation and proper orthogonal decomposition (POD) into the basic algorithm, so that pressure field of space-time two-dimensional unsteady fluid flow is fully reconstructed. Since UVP is based on ultrasound Doppler principle, the local instantaneous pressure distribution is obtained non-intrusively. The performance of an algorithm is evaluated for vortex shedding flow behind a circular cylinder at Re = 1000. Considering the specification of UVP, the optimal method of experimental data conversion to pressure information is proposed. We have found that the one-dimensional velocity measurement by UVP upon Taylor's frozen hypothesis is suitable for evaluation of pressure field in wake of the cylinder. The present algorithm is also demonstrated for opaque fluid flows by considering vortex flow in milk.
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 104 141 - 152 2019年06月 [査読有り][通常論文]
     
    This paper presents experimental findings on the behavior of bubbles moving along upper flat plates with different surface wettability in a horizontal channel. The size and velocity of the bubbles are measured by image processing to evaluate the wettability dependence in the range of channel Reynolds number, Re (2000 <= Re <= 5000) and bubble Weber number, We (1 < We < 10). When the bubbles move along a hydrophilic flat plate, their wall-sliding velocity increases with the bubble diameter, and no bubbles adhere to the plate even at low Re. By contrast, their behavior depends strongly on Re when a hydrophobic plate is used. At Re = 5000, an intrinsic cycle of coalescence and breakup of bubbles takes place. In this cycle, large wall-creeping bubbles become stretched by shear, and then each tends to break up into a small bubble that adheres to the plate surface and a medium-sized bubble that is detached from the plate. Because the small, adhered bubbles grow to large creeping bubbles through coalescence with bubbles supplied upstream, this intrinsic cycle repeats downstream. As a consequence, the hydrophobic plate produces two groups of bubbles within the turbulent boundary layer of the plate: one consisting of medium-sized free bubbles and one consisting of small wall-adhering bubbles to large wall-creeping bubbles.
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 103 66 - 77 2019年05月 [査読有り][通常論文]
     
    Frictional drag reduction due to bubble lubrication was investigated by measuring liquid films creeping along a wall within a two-phase turbulent boundary layer. We developed noninvasive time-resolved ultrasonic pulse echography for imaging a liquid film at a profiling rate of 3 kHz and a spatial resolution of 50 Various film patterns were obtained for a 4-m-long flat-bottom model ship towed in a 100-m-long water tank, where a drag reduction rate of 30% was recorded for maximum air injection. We found that the liquid-film thickness ranged from 50 to 150 wall units of the single-phase turbulent boundary layer; this film was thicker than the buffer layer depth. With an increase in the air injection flow rate, the average thickness decreased close to the buffer layer limit while the skewness and kurtosis of the probability density function of the film thickness increased. A sudden transition of the film form was detected according to the kurtosis, allowing the monitoring of the criteria of the coalescence of dispersed bubbles into large elongated bubbles via ultrasonic pulse echography.
  • Horizontal diffusive motion of columnar vortices in rotating Rayleigh-Bénard convection
    D.Noto, Y.Tasaka, Y.Murai, T.Yanagisawa
    Journal of Fluid Mechanics 871 401 - 423 2019年04月 [査読有り][通常論文]
  • Megumi Akashi, Takatoshi Yanagisawa, Yuji Tasaka, Tobias Vogt, Yuichi Murai, Sven Eckert
    PHYSICAL REVIEW FLUIDS 4 3 2019年03月 [査読有り][通常論文]
     
    Turbulent Rayleigh-Benard convection was investigated within a liquid metal layer, Prandtl number Pr = 0.03, in a square vessel having a moderate aspect ratio, Gamma = 5. Laboratory experiments were performed at moderate Rayleigh numbers, 7.9 x 10(3) < Ra < 3.5 x 10(5). Ultrasonic velocity profiling was used to visualize the spatiotemporal flow structure in two horizontal planes, while temperature fluctuations were monitored simultaneously in the fluid layer. By using multiple ultrasonic sensors, a grid of orthogonal measurement lines was created. This configuration enabled the identification of coherent flow structures showing periodic oscillations. In particular, oscillatory roll-like structures were observed for Ra less than or similar to 6 x 10(4), while the transition to a new-found, fully three-dimensional cellular structure occurs around Ra = 7 x 10(4). The Fourier analysis of the temperature fluctuations indicates that the convection reaches the developed state of thermal turbulence at this Ra number. This cellular structure of the flow field is recognized as a representation of the large-scale circulation in thermal turbulence for the specific situation of confined convection in the rectangular vessel. The transition from laminar convection to thermal turbulence manifests itself in the occurrence of unstable intermediate regimes accompanied by a stepwise increment in the horizontal scale. We suggest scaling laws for the characteristic velocity and the dominating oscillation frequency and based on that for the horizontal length scale as a function of the Ra number. The comparison to corresponding values of characteristic length scales published for thermal convection in air in larger aspect ratios [Pr = 0.7, T. Hartlep et al., Phys. Rev. Lett. 91, 064501 (2003), A. Pandey et al., Nat. Commun. 9, 2118 (2018), and D. E. Fitzjarrald, J. Fluid Mech. 73, 693 (1976)] reveals a different Ra number dependence of the horizontal wave number.
  • Xuewei Shi, Chao Tan, Feng Dong, Yuichi Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 111 219 - 231 2019年02月 [査読有り][通常論文]
     
    As a highly complex and random process, oil-gas-water three-phase flow is commonly encountered in petroleum production and transportation. Flow velocity of each individual phase is an important parameter for production estimation and flow assurance. To measure the phase velocity of three-phase flow, a one-side ultrasonic transducer working in continuous wave Doppler mode and a conductance sensor were combined to obtain the Doppler shift signal and the holdup signal. Firstly, the water holdup fluctuations were decomposed by the continuous wavelet transform to get the local wavelet energy (LWE) coefficients map on the time-frequency diagram to characterize the local flow structures of each typical flow regime. Since the ultrasound was reflected and scattered by both liquid droplets and gas bubbles, the Doppler shift signal contains fluctuations in different scales. The Doppler shift signal was then processed by the short-time Fourier transform to reveal the correlation between the time-varying velocity characteristics and the flow structure. Thirdly, the ensemble empirical mode decomposition was used to decompose the Doppler shift signal into different intrinsic mode functions (IMFs), and the first three IMFs were selected as the main IMFs. Finally, combined with the LWE coefficient map to jointly analyze the flow dynamic characteristics, the specific IMFs were found well-correlated with the flow information of the specific phases. The models for phase velocities extraction were then established. The extraction results were validated through dynamic experiments. The root mean square error of the liquid superficial velocity, the gas superficial and the overall superficial velocity are 0.06 m/s, 0.06 m/s and 0.07 m/s respectively. (C) 2018 Elsevier Ltd. All rights reserved.
  • Yuichi Murai, Daichi Saitoh, Daiki Ushiyama, Hyun Jin Park, Yuji Tasaka
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 2019年 
    How microbubbles behave inside turbulent boundary layers are investigated experimentally. Water electrolysis is applied for generation of microbubbles in water, of which electrodes are flash mounted on the solid wall in the upstream section of the measurement area. Four kinds of solid surfaces are examined to compare the microbubble distribution. For a circular cylinder of the radius R= 22 mm at Re=5,000, we found that microbubbles depart from the surface earlier than the liquid boundary layer. For an elliptic cylinder of the curvature radius of R=60 mm and a hydrofoil of NACA0040, microbubble injection made the separation point move downstream in the range of 9,000< Re< 90,000. To compare the effect with the cases of flat solid surfaces (R=infinity), we visualized three-dimensional distribution of microbubbles with color-coded volumetric illumination technique. The result has shown formation of microbubble clusters intermittently, which has Coulomb potential due to negative electric charge on bubble interfaces.
  • Taiji Tanaka, Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 2019年 
    To investigate the development process of a void wave, spatio-temporal fluctuation of void fraction, we examined experimentally a turbulent boundary layer with bubble injections. The experiments performed on a flat bottom of 4-m-long transparent model ship towed in a tank of 100 m length with the speed of up to 3.00 m/s. In bubbles injection with constant air flow rate, void fluctuations with 4 Hz or 8 Hz appeared dependent on the towing speed. With periodically fluctuated air flow rate, artificial void waves were provided into the turbulent boundary layer and their frequency was maintained during the downstream propagation. The attenuation rate of the fluctuation evaluated using Fourier analysis of the wave took the minimum value at specific injection frequency conditions.
  • Hyun Jin Park, Yuhei Sugano, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 4 2019年 
    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.
  • 田坂 裕司, 芳田 泰基, 村井 祐一
    流体工学部門講演会講演論文集 2019 OS11-01  一般社団法人 日本機械学会 2019年 [査読無し]
  • 中村 隼人, 大石 義彦, 河合 秀樹, 村井 祐一, 川北 千春, 濱田 達也
    流体工学部門講演会講演論文集 2019 0 OS2 - 19 一般社団法人 日本機械学会 2019年 

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

  • 村井 祐一, 大友 衆示, 田坂 裕司, デニセンコ ペトロ
    動力・エネルギー技術の最前線講演論文集 : シンポジウム 2019 0 C211  一般社団法人 日本機械学会 2019年 
    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.
  • 田中 泰爾, 朴 炫珍, 田坂 裕司, 村井 祐一, 川北 千春
    動力・エネルギー技術の最前線講演論文集 : シンポジウム 2019 0 A122  一般社団法人 日本機械学会 2019年 [査読有り][通常論文]
  • Ichiro Kumagai, Kakeru Taguchi, Chiharu Kawakita, Tatsuya Hamada, Yuichi Murai
    ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019 5 2019年 [査読有り][通常論文]
     
    Copyright © 2019 ASME. Air entrainment and bubble generation by a hydrofoil bubble generator for ship drag reduction have been investigated using a small high-speed channel tunnel with the gap of 20 mm in National Maritime Research Institute (NMRI). A hydrofoil (NACA4412, chord length = 40 mm) was installed in the channel and an air induction pipe was placed above the hydrofoil. The flow rate of the entrained air was quantitatively measured by thermal air flow sensors at the inlet of the air induction pipe. The gas-liquid flow around the hydrofoil was visualized by a backlight method and recorded by a high-speed video camera. As the flow velocity in the channel increased, the negative pressure generated above the suction side of the hydrofoil lowered the hydrostatic pressure in the channel, then the atmospheric air was entrained into the channel flow. The entrained air was broken into small air bubbles by the turbulent flow in the channel. The threshold of air entrainment, the air flow rate, and gas-liquid flow pattern depends on Reynolds number, angle of attack (AOA), and hydrofoil type. We identified at least three modes of air entrainment behavior: intermittent air entrainment, stable air entrainment, and air entrainment with a ventilated cavity. At high flow speed in our experimental condition (9 m/s), a large volume of air bubbles was generated by this hydrofoil system (e.g. air flow rate was 50 l/min for NACA4412 at AOA 16 degrees), which has a high potential to reduce ship drag.
  • D.Noto, Y.Tasaka, T.Yanagisawa, H.J.Park, Y.Murai
    Journal of Visualization, Vol.21, pp.987-998 21 6 987 - 998 2018年12月 [査読有り][通常論文]
     
    We established a vortex detection method using instantaneous temperature fields that were visualized using thermochromic liquid crystals (TLCs) to investigate behaviors of vortical structures in a rotating Rayleigh-Benard convection. Experimental testing was performed at a fixed Rayleigh number in water containing encapsulated TLCs. Vortices were recognized as undulations that appear in the horizontal temperature fields, thus making vortex detection with high spatial resolution possible, and this enabled quantitative investigation of the dynamics of vortical structures. Standard template matching was used to detect individual vortices on visualized temperature fields, and two-dimensional curved surface fitting was adopted to remove erroneous detections and to evaluate shapes of local temperature fields corresponding to vortical structures. Additionally, vortex tracking clearly showed geometric advection pattern of vortical structures.
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    EXPERIMENTS IN FLUIDS 59 11 2018年11月 [査読有り][通常論文]
     
    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.
  • Y.Murai, Y.Tasaka, Y.Oishi, Y.Takeda
    Experiments in Fluids, Vol. 59: 164 59 11 2018年11月 [査読有り][通常論文]
     
    Injection of bubbles into Taylor-Couette flow creates new flow modes which have not been experienced in single-phase flow conditions. An array of spiral vortices array is one such mode departing from the original toroidal Taylor vortices. The aim of the present study is to explore the mode transition of the two-phase flow using particle tracking velocimetry. Vertical-axis concentric cylinder with a rotating inner cylinder was used to measure the motion of both phases in the range 600
  • Yuichi Murai, Gretar Tryggvason
    NUCLEAR ENGINEERING AND DESIGN 337 317 - 317 2018年10月
  • Accuracy and robustness evaluations on algorithms of ultrasonic spinning rheometry
    Taiki Yoshida, Yuji Tasaka, Hyun Jin Park, Yuichi Murai
    11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering 2018年09月 [査読有り][通常論文]
  • Weiling Liu, Chao Tan, Xiaoxiao Dong, Feng Dong, Yuichi Murai
    IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT 67 9 2129 - 2142 2018年09月 [査読有り][通常論文]
     
    Oil-water two-phase flow commonly exists in many industries. The accurate measurement of flow velocity is beneficial for safety operation and economic efficiency. A combination of a pulse-wave ultrasonic Doppler (PWUD) sensor and a conductance/ capacitance (CCC) sensor is proposed for flow velocity measurement in dispersed oil-water two-phase flow. The PWUD sensor estimates dispersed phase velocity', and the CCC sensor provides phase fraction. The overall superficial flow velocity (J) and individual flow velocities are estimated by combining the outputs of the two sensors. The dual-modality sensing system was designed and experimentally verified on a horizontal multiphase flow loop. Ignoring the slippage between two phases, the J is estimated with an average relative error (ARE) of 5.58%, water superficial velocity with 6.42%, and oil superficial velocity with 6.91%. To further improve the measurement accuracy, slip velocity-based measurement model is presented by introducing the drift-flux model. The distribution parameter of this model is derived from theoretical analysis. The correlation between relative velocity and J is analyzed by the force analysis of dispersed phase in water/oil-continuous flow theoretically and experimentally. The results demonstrate that the proposed model estimates the J with an ARE of 2.21%, water superficial velocity with 3.56%, and oil superficial velocity with 3.80%. Besides, ARE of different flow patterns shows a uniform distribution. The slip velocity-based measurement model has an advantage of less error in overall superficial flow velocity estimation, reduced by 60% compared with that of the nonslip velocity-based measurement model.
  • Rheological properties of montmorillonite dispersions in dilute NaCL concentration investigated by ultrasonic spinning rheometry
    T.Yoshida, Y.Tasaka, S.Tanaka, H.J.Park, Y.Murai
    Applied Cray Science, Vol.161, pp.513-523 2018年04月 [査読有り][通常論文]
  • Taiki Yoshida, Yuji Tasaka, Hyun Jin Park, Yuichi Murai, Hiroki Teramura, Shigenobu Koseki
    JOURNAL OF VISUALIZATION 21 2 253 - 265 2018年04月 [査読有り][通常論文]
     
    We proposed a novel ultrasonic Doppler-echo visualization method that is expected to realize nondestructive visualization using an ultrasonic velocity profiler. The visualization uses information of both the Doppler velocity and echo intensity that have usually been used by the ultrasonic velocity profiler to obtain instantaneous velocity profiles. The feasibility of the method is confirmed by measurements of a rubber ball, apple, and tomato having different acoustic impedances, pulp hardnesses, shapes, and inner structures. Mathematical relations and image processing parameters were discussed to obtain images of the inner structures of test objects using the ultrasonic velocity profiler. Trial measurements of test objects elucidated that the Doppler velocity and echo intensity detect different features of the test objects. Using the Doppler velocity and echo intensity, the outlines and inner structures of the objects can be visualized.
  • Yuji Tasaka, Taiki Yoshida, Richard Rapberger, Yuichi Murai
    RHEOLOGICA ACTA 57 3 229 - 240 2018年03月 [査読有り][通常論文]
     
    To achieve a stable evaluation of the linear viscoelasticity of bubble suspensions, which have difficulties for conventional rheometers from spatial distributions of rheological properties with bubble deformations, we proposed a novel rheometry based on spatio-temporal velocity data obtained by ultrasonic velocity profiling (UVP). A frequency-domain algorithm was adopted to overcome a critical influence of measurement noise on the rheological assessment, which is inferred from error propagation characteristics through the equations of motion in discretized form. Applicability and advantage of the present rheometry with the frequency-domain algorithm were verified by two kinds of fluids: high viscous oil as a Newtonian fluid and polyacrylamide aqueous solution as a shear thinning, viscoelastic fluid. The rheometry was finally adopted for bubble suspensions subject to high oscillatory shear, and it could validly extract elasticity-originated momentum transfer as a function of space.
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 113 1200 - 1211 2017年10月 [査読有り][通常論文]
     
    Natural convection heat transfer from a heated wall in water with near-wall injection of millimeter-sized bubbles is studied experimentally. Velocity and temperature measurements are conducted in the near wall region. In the range of the heated wall angles from 0 to 417 from the vertical, the heat transfer coefficient increases by up to an order of magnitude with bubble injection. The ratio of the heat transfer coefficient with bubble injection to that without injection increases with the wall inclination angle. Based upon measured liquid temperature distributions and liquid flow velocity profiles, enhancement of heat transfer by bubble injection is explained by two mechanisms. First, wall-parallel transport of cold liquid into the thermal boundary layer is enhanced by the bubble-driven flow. Second, wall-normal mixing of warm liquid and cold liquid occurs, as a result of wall-normal velocity fluctuations of the liquid phase activated by a combination of bubble rising motion, vortex shedding from the bubbles, and unsteady vortices formed within the boundary layer. The unsteady vortices travel along the wall together with the bubbles, primarily contributing to the enhancement of heat transfer at higher wall inclination angles. (C) 2017 Elsevier Ltd. All rights reserved.
  • Bruno van Ruymbeke, Yuichi Murai, Yuji Tasaka, Yoshihiko Oishi, Celine Gabillet, Catherine Colin, Noureddine Latrache
    JOURNAL OF VISUALIZATION 20 2 349 - 358 2017年05月 [査読有り][通常論文]
     
    We develop a novel method to study the gas phase features in a bubbly Taylor-Couette flow when bubbles are arranged as elevated toroidal strings. The flow is recorded in the front view plane with a highspeed camera for a Reynolds number of 1500 and a global void fraction of 0.14 %. An image processing algorithm is developed to discriminate bubbles accumulated in clouds near the inner cylinder (cloud bubbles) from bubbles trapped in the bulk flow by vortices (swirl bubbles). The analysis of the preferential positions, azimuthal velocities, and equivalent void fraction of clouds and swirl bubbles separately provides a new insight into the dynamics of the bubble's entrapment.
  • Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    JOURNAL OF RHEOLOGY 61 3 537 - 549 2017年05月 [査読有り][通常論文]
     
    We propose a rheometry using ultrasonic velocity profiling (UVP) that visualizes and evaluates quantitatively opaque complex fluids in a cylindrical open vessel performing unsteady rotation. The methodology termed "ultrasonic spinning rheometry (USR)" is expected to provide details of various rheological properties. In our study of USR applications, an enhancement in measuring some rheological properties was achieved for three different non-Newtonian fluids. For quantitative evaluations, we focused on momentum propagation in unsteady shear flows from an oscillating cylindrical container. In such flows, this propagation is represented in the radial profiles of the phase lag of velocity fluctuations. The phase lag information is obtained by a discrete Fourier transform of the spatio-temporal velocity distributions measured using UVP and indicates that the phase lag changes substantially as rheological properties change in a test fluid. As the primary rheological property, a local effective viscosity that is representative of the Newtonian viscosity in the bulk of a measurement volume is determined using UVP. In addition, the shear stress distribution, yield stress, spatial viscosity profile, and shear modulus are obtained as secondary rheological properties. (C) 2017 The Society of Rheology.
  • 中村幸太郎, 田坂裕司, 村井祐一
    混相流, Vol. 31 2017年04月 [査読有り][通常論文]
  • 中村幸太郎, 田坂裕司, 村井祐一, 田坂裕司
    本混相流学会論文集 31 1 20 - 28 2017年01月 [査読有り][通常論文]
  • J.Hitomi, Y.Murai, H.J.Park, Y.Tasaka
    IEEE Access, Vol.5 5 15021 - 15029 2017年 [査読有り][通常論文]
     
    The combined use of ultrasound pulse-echo intensity and Doppler shift frequency is examined as a means to measure strong unsteady three-phase pipe flows of a gas and two liquids. With air, oil, and water as components of the fluid media, particular attention is given to analyze ultrasound responses at the air-oil and oil-water interfaces. Reciprocating slugging is generated inside a 55-mm-diameter circular pipe, of which edges oscillate vertically at a controlled frequency. We use an ultrasound velocity profiler to obtain the 1-D cross-sectional distributions of the instantaneous flow velocity at the sampling rate of 60 Hz. All the measurements are realized by a single ultrasound transducer located outside the pipe. Measurement accuracy is validated using a high-speed camera coupled with particle image velocimetry that is synchronized with the profiler. The results demonstrate that the proposed technique works properly in sensing both interfaces as well as in-phase flow velocity distributions. In addition, multiphase volume flow rates for the constituents are obtained by velocity profile integration assuming vertical phase stratification in an approximation.
  • Atsuhide Kitagawa, Petr Denissenko, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 80 126 - 138 2017年01月 [査読有り][通常論文]
     
    This paper presents an experimental study of the influence of wall surface wettability on the behavior of hydrogen microbubbles rising along a nearly vertical wall. Multiple optical diagnostics, including particle tracking velocimetry, have been employed for the study. The microbubble behavior observed along three different kinds of wall surfaces (hydrophobic, hydrophilic, and super-hydrophilic) was characterized by the microbubble-wall attachment, bubble size distribution, bubble coalescence, and microbubble layer formation. Microbubbles rising along the wall with poor wettability soon attach to the wall and grow to millimeters in size as a result of bubble coalescence. Such millimeter-sized bubbles detach from the wall because of their increased buoyancy, and eventually enhance transverse diffusion of microbubbles, which is known as the sweep-out effect. In contrast, in the case of very good wettability, almost no microbubbles attach to the wall and smoothly form a thin microbubble layer in the wall proximity. The observed phenomena contradict our intuitive expectation of the effect of surface wettability on gas bubbles, and hence may be regarded as a feature of microbubbles that distinguishes them from large bubbles. (C) 2016 Elsevier Inc. All rights reserved.
  • Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 27 12 2016年12月 [査読無し][招待有り]
  • Hyun Jin Park, Yoshihiko Oishi, Yuji Tasaka, Yuichi Murai
    EXPERIMENTS IN FLUIDS 57 12 2016年12月 [査読有り][通常論文]
     
    The injection of bubbles into a turbulent boundary layer can reduce the skin friction of a wall. Conventionally, the drag reduction rate is evaluated using time-averaged quantities of the mean gas flow rate or mean void fraction. Actually, as bubbles are subject to strong shear stresses near the wall, void waves and local bubble clusters appear. For pipe and channel flows, such wavelike behavior of the dispersed phase has been investigated intensely as an internal two-phase flow problem. We investigate how this wavy structure forms within the boundary layer as an external spatially developing two-phase flow along a horizontal flat plate. We describe how our model ship is designed to meet that purpose and report bubble-traveling behavior that accompanies unexpectedly strong wavy oscillations in the streamwise direction. A theoretical explanation based on a simplified two-fluid model is given to support this experimental fact, which suggests that void waves naturally stand out when drag reduction is enhanced through the local spatial gradient of the void fraction.
  • Tomoaki Takeuchi, Jumpei Ohkubo, Norio Yonezawa, Yoshihiko Oishi, Ichiro Kumagai, Yuji Tasaka, Yuichi Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 87 45 - 53 2016年12月 [査読有り][通常論文]
     
    Internal gas velocity fluctuations and their effects on the mist diffusion process were examined in a long horizontal pipe to understand oil mist transportation, particularly in the laminar-to-turbulent flow transition region. Three hot-wire anemometers and aerosol concentration monitors were used to deduce these effects as the two-phase mist flow gradually developed in the stream-wise direction. We found significant axial mist diffusion at Reynolds numbers (Re) < 1000 because of passive scalar transport by Poiseuille flow. However, this diffusion was restricted by the non-zero inertia of the mist at a Stokes number, 0(10(-5)), relying on the Brownian motion of the mist. At Re > 2400, a sharp mist waveform was maintained by a turbulent flow with active radial mixing. New data were obtained within the range of 1000 < Re < 2400, which cannot be explained by interpolation between the above-mentioned two states. The mist concentration displays multiple temporal peaks at Re < 2000 owing to perturbations of localized turbulence as well as radial anisotropy as being conveyed more than 2000-diameters in distance. This behavior is caused by intermittent disturbances induced by the pipe wall roughness, which sharply distorts the wall-aligned laminar mist layer left by parabolic axial stretching of local laminar flow. (C) 2016 Elsevier Ltd. All rights reserved.
  • Jumpei Ohkubo, Yuji Tasaka, Hyun Jin Park, Yuichi Murai
    JOURNAL OF VISUALIZATION 19 4 643 - 651 2016年11月 [査読有り][通常論文]
     
    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..
  • 水平液体層内を上昇運動する気泡により引き起こされる流れの不安定性
    中村, 吉川, 田坂, 村井
    日本流体力学会年会講演論文集 2016年09月 [査読有り][通常論文]
  • Quantitative evaluation of rheological properties for complex fluids using ultrasonic spinning rheometry
    Taiki Yoshida, Yuji Tasaka, Yuichi Murai
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering (ISUD 10) 2016年09月 [査読有り][通常論文]
  • Takahiro Nakashima, Takahisa Shiratori, Yuichi Murai, Yuji Tasaka, Yasushi Takeda, Eric J. Windhab
    FLOW MEASUREMENT AND INSTRUMENTATION 48 97 - 103 2016年04月 [査読有り][通常論文]
     
    Ultrasound velocity profiling was applied to viscoelastic flow induced around a moving permeable disk. There were two objectives to this measurement. The first was to find technical advantages and restrictions when applying ultrasonic Doppler velocimetry to a viscoelastic liquid. This issue has not been clarified even though ultrasonic pulses may interact with an elastic medium in the monitoring of the Doppler shift frequency. The second objective was to determine the fluid physics of a viscoelastic liquid around a permeable object, which will help in designing mixing process for materials subject to strong rheological resistance. In this paper, we report a representative response of a viscoelastic liquid in terms of its spatiotemporal velocity distribution. The response highlighted is cyclic lateral waves that form behind the disk, which were hardly detectable by particle image velocimetry. We discuss multiple reasons for this phenomenon considering not only fluid properties but also the measurement principle of ultrasound velocity profiling as applied to viscoelastic liquid. (C) 2015 Elsevier Ltd. All rights reserved.
  • Takahisa Shiratori, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 71 1 - 13 2016年02月 [査読有り][通常論文]
     
    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.
  • 佐藤 牧, 田坂 裕司, 村井 祐一
    北海道支部講演会講演概要集 2016 61 - 62 一般社団法人 日本機械学会 2016年
  • Shuji OTOMO, Susumu OSUKA, Yuji TASAKA, Yuichi MURAI, Petr DENISSENKO
    The Proceedings of Conference of Hokkaido Branch 2016.54 0 79 - 80 2016年
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 26 12 2015年12月 [査読有り][通常論文]
     
    The behavior of a bubbly two-phase flow in the vicinity of a wall affects heat, mass, and momentum transfer; therefore, there is great interest in developing a quantitative technique to monitor this behavior. Herein we propose a new method based on ultrasound echo signal processing that it feasible for industrial applications where the boundary layer is modified by traveling bubbles. By introducing time-resolved direct waveform analysis at 100 MHz, we have succeeded in the spatio-temporal detection of bubble surfaces at echographic profiling frequencies in the range of 15-20 kHz. Unlike conventional approaches, which use short pulses, a relatively long pulse length is applied to allow ultrasound Doppler velocimetry in the liquid phase. Examination of the horizontal bubbly two-phase turbulent channel flows demonstrated the feasibility of this method; spatio-temporal echography of moving bubble surfaces is successfully achieved as the bubbles travel on length scales smaller than the spatial ultrasonic pulse length near the wall. The applicable range of parameters (e.g. bubble size and shape, and flow speed) was determined by 3D numerical analysis of the wave equation and its application to bubbles flowing beneath a flat-bottom model ship.
  • Hyun Jin Park, Yuji Tasaka, Yoshihiko Oishi, Yuichi Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 75 12 - 25 2015年10月 [査読有り][通常論文]
     
    To promote the efficiency of frictional drag reduction using bubbles, we designed a novel bubble control method that involves repetitive injection of bubbles rather than the conventional continuous bubble injection approach. Even if the mean void fraction of bubbles to be injected into the turbulent boundary layer is set to be low, repetitive bubble injection (RBI) maintains the frictional drag reduction by generating bubble swarms. The enhanced drag reduction mechanism and the effectiveness of the RBI approach are investigated by studying wall shear stress and the velocity vector field in the liquid phase when measured in a turbulent horizontal channel flow. The bubble swarms generated by RBI consist of bubbles of various sizes with leading large air films, which have high reproducibility. The leading air films, which are a result of the concentrated void fraction, maintain a high drag reduction effect by air lubrication and by suppression of Reynolds shear stress events in the turbulent vortical structures beneath the bubble swarm. The latter effect of RBI in particular plays a significant role at higher Reynolds numbers. Based on the combination of these effects, we confirmed that RBI provides an extra drag reduction effect when compared with continuous bubble injection. (C) 2015 Elsevier Ltd. All rights reserved.
  • Takahisa Shiratori, Yuji Tasaka, Yoshihiko Oishi, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 26 8 2015年08月 [査読有り][通常論文]
     
    We propose a new rheometry for characterizing the rheological properties of fluids. The technique produces flow curves, which represent the relationship between the fluid shear rate and shear stress. Flow curves are obtained by measuring the circumferential velocity distribution of tested fluids in a circular Couette system, using an ultrasonic velocity profiling technique. By adopting a widened gap of concentric cylinders, a designed range of the shear rate is obtained so that velocity profile measurement along a single line directly acquires flow curves. To reduce the effect of ultrasonic noise on resultant flow curves, several fitting functions and variable transforms are examined to best approximate the velocity profile without introducing a priori rheological models. Silicone oil, polyacrylamide solution, and yogurt were used to evaluate the applicability of this technique. These substances are purposely targeted as examples of Newtonian fluids, shear thinning fluids, and opaque fluids with unknown rheological properties, respectively. We find that fourth-order Chebyshev polynomials provide the most accurate representation of flow curves in the context of model-free rheometry enabled by ultrasonic velocity profiling.
  • Yuichi Murai, Takahisa Shiratori, Ichiro Kumagai, Patrick A. Ruehs, Peter Fischer
    FLOW MEASUREMENT AND INSTRUMENTATION 41 121 - 128 2015年03月 [査読有り][通常論文]
     
    An experimental method for measuring the effective viscosity of two dimensional dispersion systems is proposed. The method is based on interfacial rheology, which was originally developed to investigate surface active adsorption layers such as protein film formed at liquid-liquid interfaces. Bubbles or rigid particles at around 50% of volume fraction in liquid are positioned in the gap between a rotating disk and a stationary cylindrical container. With this configuration, shear-rate dependent effective viscosities of bubble and particle layers were investigated. Steep shear-thinning property is observed for spherical bubble systems in the shear rate regime from 10(-1) to 10(2) s(-1). This is explained by topological transition from regular to random arrangement of the bubbles at the interface. For rigid particle systems, the viscosity starts from high value due to solid contact friction, then decreases sharply due to fluidization process until inter-particle collision lead to an increase of the viscosity. (C) 2014 Elsevier Ltd. All rights reserved.
  • Yuichi Murai, Takahisa Shiratori, Ichiro Kumagai, Patrick A. Ruehs, Peter Fischer
    FLOW MEASUREMENT AND INSTRUMENTATION 41 121 - 128 2015年03月 [査読有り][通常論文]
     
    An experimental method for measuring the effective viscosity of two dimensional dispersion systems is proposed. The method is based on interfacial rheology, which was originally developed to investigate surface active adsorption layers such as protein film formed at liquid-liquid interfaces. Bubbles or rigid particles at around 50% of volume fraction in liquid are positioned in the gap between a rotating disk and a stationary cylindrical container. With this configuration, shear-rate dependent effective viscosities of bubble and particle layers were investigated. Steep shear-thinning property is observed for spherical bubble systems in the shear rate regime from 10(-1) to 10(2) s(-1). This is explained by topological transition from regular to random arrangement of the bubbles at the interface. For rigid particle systems, the viscosity starts from high value due to solid contact friction, then decreases sharply due to fluidization process until inter-particle collision lead to an increase of the viscosity. (C) 2014 Elsevier Ltd. All rights reserved.
  • Ichiro Kumagai, Yoshiaki Takahashi, Yuichi Murai
    OCEAN ENGINEERING 95 183 - 194 2015年02月 [査読有り][通常論文]
     
    We have developed a new power-saving device to reduce the drag of a ship's hull using small bubbles. The device reduces the energy required for bubble generation. The device, which consists of angled hydrofoils with air introducers, uses the low-pressure region produced above the hydrofoil as the ship moves forward to drive atmospheric air into the water. We describe the device principles obtained from simple fluid dynamic theory, and, through experiments performed in a small towing tank, show the fundamental air entrainment and bubble generation processes for the flow behavior around a hydrofoil beneath a free surface. We also present a semi-empirical scaling process for practical application to full-size ships to estimate the net drag reduction achieved by this device. Finally, the results of a series of full-scale tests are reported and show that, with correct operation, our device can produce a net power saving of 5-15% for ships. (C) 2014 The Authors. Published by Elsevier Ltd.
  • Y. Tasaka, T. Kimura, Y. Murai
    EXPERIMENTS IN FLUIDS 56 1 2015年01月 [査読有り][通常論文]
     
    We have proposed a novel methodology using ultrasonic velocity profiling to estimate the effective viscosity of bubble suspensions that are accompanied by non-equilibrium bubble deformations in periodic shear flows. The methodology was termed "ultrasonic spinning rheometry" and validated on measurement of the effective viscosity of particle suspensions that has a semi-empirical formula giving good estimation of the actual viscosity. The results indicated that the proposed technique is valid for particle volume fractions below 3.0 %. Applying this to bubble suspensions suggested that the effective value of temporal variations in the capillary number, Carms, is an important indicator to distinguish regimes in estimating the effective viscosity: Unsteady flows having larger Carms number than the critical capillary number for the deformation of bubbles are categorized into Regime 2 that includes both highly unsteady conditions and large steady deformation of bubbles.
  • Atsuhide Kitagawa, Yuichi Murai
    CHEMICAL ENGINEERING SCIENCE 116 694 - 703 2014年09月 [査読有り][通常論文]
     
    Based on the experimental finding that microbubble swarms dramatically promote heat transfer from a vertical heated wall, despite their potentially adiabatic nature, tests of microbubble fluid mechanics in the isothermal state are performed to clarify the unique motion characteristics of microbubble swarms. At constant bubble flow rate, the microbubble swarm shows a significant pulsatory rise along a vertical flat wall, particularly for small bubbles. Particle tracking velocimetry applied to the microbubbles shows that a two-way interaction between the microbubbles and the liquid flow self-excites the pulsation during their co-current rise. The sequence consists of the following processes: (i) increase in the bubble number density close to the wall as a result of the liquid velocity gradient driven by the microbubbles themselves; (ii) wave generation inside the microbubble swarm to induce the pulsatory rise of the swarm; and (iii) amplification of the waves, which results in void-bursting motion in the final stage. (C) 2014 Elsevier Ltd. All rights reserved.
  • Hyun Jin Park, Yuji Tasaka, Yuichi Murai, Yoshihiko Oishi
    CHEMICAL ENGINEERING SCIENCE 116 486 - 496 2014年09月 [査読有り][通常論文]
     
    Bubbles injected into a wall turbulent boundary layer can modify heat, mass, and momentum transfers of the wall. One factor responsible for the phenomenon is alternation of the vortical flow structures near the wall. To demonstrate this graphically, we directly visualized the interaction between the vortical flow structures and a bubble swarm composed of bubbles with various sizes, by means of two-color laser-sheet illumination of the wall turbulence with a dilute suspension of flakes. Image processing realized quantitative characterization of interaction events in the buffer and logarithmic layers, referring to multiple measured quantities such as the relative advection velocity between bubbles and turbulence, spacing of vortices both in streamwise and spanwise directions, persisting lengths of vortices in both directions, and statistical inclination angles of the streamwise vortices. A particular finding from the present visualization is that the streamwise vortices in the buffer layer were swept by the bubble swarm but brought to the backside of the swarm to survive until the swarm passed by. (C) 2014 Elsevier Ltd. All rights reserved.
  • Yuichi Murai
    EXPERIMENTS IN FLUIDS 55 7 2014年07月 [査読有り][招待有り]
     
    The injection of gas bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. This explains why a number of different void-drag reduction relationships have been reported to date, while early works pursued a simple universal mechanism. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. Each regime has inherent physics of bubbly liquid, highlighted by keywords such as bubbly mixture rheology, the spectral response of bubbles in turbulence, buoyancy-dominated bubble behavior, and gas cavity breakup. Among the regimes, bubbles in some selected situations lose the drag reduction effect owing to extra momentum transfer promoted by their active motions. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. This article reviews the roles of bubbles in drag reduction, which have been revealed from fundamental studies of simplified flow geometries and from development of measurement techniques that resolve the inner layer structure of bubble-mixed turbulent boundary layers.
  • Transition of flow structure at marginal conditions in internally heated convection with background rotation
    Y.YAMAGUCHI, Y.TASAKA, Y.OISHI, Y.MURAI, T.YANAGISAWA
    Asia Oceania Geosciences Society 2014 USB  2014年07月 [査読無し][通常論文]
  • Investigation of cell patterns on a rotating convection by ultrasonic velocity profile measurements
    K.FUJITA, Y.TASAKA, Y.OISHI, Y.MURAI, T.YANAGISAWA
    Asia Oceania Geosciences Society 2014 USB  2014年07月 [査読無し][通常論文]
  • Visualization of bubble motion in a horizontal channel using different surface conditions
    A.KITAGAWA, M.GOTO, Y.KIMURA, Y.OISHI, Y.MURAI
    16th International Symposium on Flow Visualization 2014 Okinawa ISFV16-1060 1 - 10 2014年06月 [査読有り][通常論文]
  • Measurement of Bubble cluster formed in a horizontal Turbulent channel flow
    Y.OISHI, T.TASAKA, Y.MURAI, Y.TOHGE
    16th International Symposium on Flow Visualization 2014 Okinawa ISFV16-1279 1 - 11 2014年06月 [査読有り][通常論文]
  • Yoshihiko Oishi, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 55 128 - 139 2014年05月 [査読有り][通常論文]
     
    Flow field modified by a single large bubble in a horizontal wall turbulent boundary layer is measured by particle tracking velocimetry. We focus on intermediate bubble size being comparable to the thickness of boundary layer to find out the events altering the original turbulent shear stress field. The results are all presented by quantities relative to single phase flow on Lagrangian grid system that moves with the bubble. The measurement results reveal bubble-produced secondary flow around itself, which involves twin roll vortices, separation on the bubble surface, and strong sweeping flow. For a small and nearly spherical bubble, the sweeping flow is provided strongly to enhance the turbulent momentum exchange while negative exchange is detected for a large flat bubble. This effective length approximately corresponds to the size of the bubble. (C) 2014 Elsevier Inc. All rights reserved.
  • 北川 石英, 奥 達明, 大里 拓也, 村井 祐一
    日本機械学会論文集 80 811 TEP0044 - TEP0044 The Japan Society of Mechanical Engineers 2014年 
    This paper presents the temperature and velocity measurements to clarify effects of inclination angle of a heated plate φ on natural-convection heat transfer enhancement by millimeter bubbles. In the range 0≤φ≤30˚, the heat transfer coefficient with bubble injection is much higher than that without injection, and the ratio of the heat transfer coefficient with bubble injection to that without injection (heat transfer coefficient ratio) ranges from 3.0 to 5.0. This is due to enhancement of both the transport of the warm liquid toward the downstream region and the mixing of warm liquid and cool liquid. The former results from the bubble-induced liquid entrainment, and the latter is mainly due to the increase in the liquid velocity fluctuation induced by a combination of the bubble motion and the vortex shedding from the bubble interface. Moreover, the significant bubble-induced liquid entrainment and the unsteady vortex occur near the heated wall at higher inclination angle of the heated plate. Hence, the heat transfer coefficient ratio increases with increasing inclination angle of the heated plate.
  • Norio Yonezawa, Yoshihiko Oishi, Yuji Tasaka, Yuichi Murai
    8TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1592 177 - 186 2014年 [査読有り][通常論文]
     
    As small solid particles are mixed in gas flow in a horizontal pipe, the particles are sometimes long suspended downstream due to dynamic interaction between two phases in turbulent states. Dunes of such particles are naturally formed at the bottom of the pipe in case of heavy flow rate of particles, and the dunes rather help the particles with suspension further downstream. In this study, PTV has been applied for measurement of such particles floating inside a horizontal pipe behind a synthetic dune. Time-resolved PTV analysis of the particle behavior in the section perpendicular to the mainstream has revealed that long-suspended particles keep floating with fountain like convection pattern inside the circular pipe, which consists of ascending flow at the center of the pipe, bouncing flow at the wall, and downwash at the oblique part. The present paper shows their dynamic statistics of the particle behavior for the cross-sectional distributions of concentration, velocity vector, and acceleration vector.
  • Ichiro Kumagai, Yuichi Murai, Yoshiaki Takahashi, Haruki Sakamaki, Takahiro Tsukahara, Tsubasa Ozaki, Yuji Tasaka, Yoshihiko Oishi
    8TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1592 322 - 328 2014年 [査読有り][通常論文]
     
    We have invented two types of hydrofoil bubble generator for drag reduction of ship that can reduce the energy for air bubble generation on the ship hull. Their fundamental process of air entrainment and subsequent bubble generation by the hydrofoil facility are described by a simple fluid dynamic model. We experimentally determined the critical velocity of the bubble generation and the relationship between air volume flow rate and the hydrofoil velocity. The magnitude of the negative pressure produced above the hydrofoil, which is a driving force of the air entrainment, depends on the shape of the hydrofoil, gap ratio (normalized depth of the hydrofoil), Reynolds number, Froude number, and angle of attack. Recent applications of the drag-reduction technology with air bubbles to a ship save about 10%-15% of the total energy consumption of the ship. The device works as a self-priming pump when the draft of the ship is shallow (< similar to 5 m) as predicted by the theory. For ships of deeper draft, the device needs the assistance of an air compressor. Because the magnitude of the negative pressure above the hydrofoil depends on the flow condition around the hydrofoil, proper operation of compressors is necessary. We also show experimental results on optimization of hydrofoils to enhance the hydrofoil performance of air entrainment and air bubble generation.
  • Atsuhide Kitagawa, Takuya Mimura, Masaaki Ishikawa, Yuichi Murai
    JOURNAL OF VISUALIZATION 16 4 313 - 321 2013年11月 [査読有り][通常論文]
     
    We use visualization to investigate the structure of the counter-current convection induced by microbubbles and small particles. In particular, we study the effect of small particles with different specific gravities on the gas-phase flow. In our experiments, microbubbles are injected into stationary liquid from a bubble generator that is set at the bottom of a vertical channel, and small particles are injected from a particle injector that is set at the top of the channel. The mean kinetic energy of the gas-phase is significantly lower in the flow with microbubbles and small particles than in the flow with only microbubbles. This results from significant suppression of the interaction of bubble plumes by the small particles. Moreover, the mean kinetic energy of the gas-phase in the flow with microbubbles and small particles is strongly dependent on the specific gravity of the small particles.
  • Takahisa Shiratori, Yuji Tasaka, Yuichi Murai, Yasushi Takeda
    JOURNAL OF VISUALIZATION 16 4 275 - 286 2013年11月 [査読有り][通常論文]
     
    In the field of rheology, properties of non-Newtonian fluids have been traditionally represented on graphs such as viscosity curves. In this paper, we propose a visualizer to express the fluid properties as visualized fluid motions in a rotating cylinder. To highlight different fluid motions, three patterns of rotation were given to the cylinder: rapid start of constant rotation (spin-up), rapid stop from constant rotation (spin-down), and periodic rotation. Relationships between fluid motion and fluid properties are discussed by comparing velocity profiles for three fluids: silicone oil, yogurt, and a polyacrylamide (PAA) solution. Ultrasonic velocity profiler (UVP) was used to obtain spatio-temporal velocity maps. The velocity maps reflect essential rheological properties, such as shear thinning, yield stress, and elasticity. Two additional display modes are proposed to explore fluid motions due to viscoelasticity of the PAA solution and yogurt: a grid deformation field and a shear rate field. These two visualizations can provide intuitive understanding of viscoelasticity because deformation and shear rate determine elastic and viscous stresses, respectively. In spin-down tests, the recovery of deformed grids, which is caused by elasticity, can be explicitly observed. Further, the shear rate distributions indicate that kinetic energy of the fluid dissipates near the lateral wall right after the wall stops rotating. In short, these two quantity fields visualize energy conversion among kinetic, elastic, and thermal energy; such energy conversions are characteristic of viscoelastic fluids.
  • Yuichi Murai, Jozef H. A. Vlaskamp, Yuichi Nambu, Takahiro Yoshimoto, Mark A. Brend, Petr Denissenko, Peter J. Thomas
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 51 342 - 353 2013年11月 [査読有り][通常論文]
     
    A new simple optical method for visualizing flow structures generated in a rotating flow is presented. The method consists of planar PTV with sheet illumination slightly offset to the rotation axis and a geometric reconstruction of velocity vector field under the assumption of azimuthal periodicity. Two types of columnar flows intrinsically associated with rotating flows are investigated with the method. The two types of flow are a local columnar wake induced behind a moving sphere, and an asymmetrically precessing Taylor Column created below a spinning disk. By means of this new technique we obtain the first quantitative visualization of the columnar wake and the three-dimensional structure of the Taylor Column. (C) 2013 Elsevier Inc. All rights reserved.
  • Time-Resolved Measurement of Frictional Drag Reduction by Bubbles with Void Waves
    Y.OISHI, T.WATAMURA, Y.TASAKA, Y.MURAI
    The 12th International Symposium on Fluid Control, Measurement and Visualization (FLCOME2013) OS8-03-2 USB  2013年11月 [査読有り][通常論文]
  • H.SAKAMAKI, I.KUMAGAI, Y.OISHI, Y.TASAKA, Y. MURAI
    4th International Conference on Jets, Wakes and Separated Flows, (ICJWSF-2013) 2013 4 ICJWSF2013-1051, pp.1-6 (CD-RO - 1"-"1051-6" 一般社団法人日本機械学会 2013年09月 [査読有り][通常論文]
     
    With the aim of optimizing performance of a hydrofoil bubble introducer for drag reduction of ship, the flows and free surface deformation around a hydrofoil were investigated experimentally in a wide range of Reynolds number, Froude number, gap ratio (normalized depth), and angle of attack. Image processing for the obtained images of flows and free surface elucidated the key factor of the free surface deformation and the conditions of flow separation on hydrofoils. Flow fields around the hydrofoil determined by PTV represent influence of the free surface with large deformation on the flow field quantitatively. These results provide fruitful information for the optimization of this hydrofoil facility.
  • Structure of a Vortex Ring Impacting on a Solid Boundary with Background Rotation
    Y.AIKAWA, Y.NAMBU, Y.OISHI, Y.TASAKA, Y.MURAI, P.J.THOMAS
    4th International Conference on Jets, Wakes and Separated Flows, (ICJWSF-2013) ICJWSF2013-1062, pp.1-6 (CD-RO  2013年09月 [査読有り][通常論文]
  • Atsuhide Kitagawa, Yuichi Murai
    CHEMICAL ENGINEERING SCIENCE 99 215 - 224 2013年08月 [査読有り][通常論文]
     
    The effects of microbubble injection on natural convection heat transfer from a vertical heated plate in water are experimentally investigated. Thermocouples are used to measure the temperature, and an image processing technique is used to obtain the bubble diameter, bubble velocity, and bubble layer thickness. Tap water is used as the working liquid, and hydrogen bubbles generated by water electrolysis are used as the microbubbles. At a constant wall heat flux, microbubble injection significantly increases the heat transfer coefficient in both the laminar and transition regions. The ratio of the heat transfer coefficient with bubble injection to that without injection is 1.6-2.0 in the laminar region and 1.5-2.0 in the transition region. The enhancement of heat transfer in the laminar region results from both the forced convection and mixing effects. In contrast, the enhancement of heat transfer in the transition region arises mainly because microbubble injection accelerates the transition to turbulence. (C) 2013 Elsevier Ltd. All rights reserved.
  • Miyuki Yamada, Yuichi Murai, Ichiro Kumagai
    JOURNAL OF VISUALIZATION 16 3 247 - 257 2013年08月 [査読有り][通常論文]
     
    A new method for visualization of stories in literary works was explored. Our story visualization method consists of two parts: keyword-based statistical analysis for multiple themes and imagery expression of the results for visual understanding. In this study, we focused on novels as the targets, and discussed ways in which complex structures can be simultaneously visualized using multiple themes. The method was applied for the comparison of Charles Dickens' novels with Shakespeare's plays in order to identify any existing evidence concerning literal interest created by the overlapping of multiple scenarios in a single story. We also applied the method to non-literary documents such as newspaper articles, and showed that these documents contain simple statistic patterns regarding a given theme, which contrasts with the case involving novels that include the dynamic fluctuation of individual story elements.
  • Color Tomographic PIV Improved by Removal of Color Contamination
    Y.MURAI, T.YUMOTO, Y.OISHI, Y.TASAKA
    The 10th International Symposium on Particle Image Velocimetry PIV2013 USB, pp.1-8  2013年07月 [査読有り][通常論文]
  • Dynamic 1D-2C PTV for boundary layer measurement
    Y.OISHI, Y.MURAI
    The 10th International Symposium on Particle Image Velocimetry PIV2013 P19, USB, p.187  2013年07月 [査読有り][通常論文]
  • T.Watamura, Y.Tasaka, Y.Murai
    Physics of Fluids 25 5 2013年05月 [査読有り][通常論文]
     
    The effect of the presence of microbubbles on a flow state is experimentally investigated in a Taylor-Couette flow with azimuthal waves, in order to examine the interaction mechanism of bubbles and flows that result in drag reduction. The average diameter of the bubbles is 60 mu m, which is smaller than the Kolmogorov length scale, and the maximum void fraction is 1.2x10(-4) at the maximum case. The modifications of the fluid properties, bulk density, effective viscosity, and the extra energy input caused by the addition of microbubbles are expected to have a small effect on modifying flow states. The power of the basic wave propagating in the azimuthal direction is enhanced; its modulation, however, is decreased by adding microbubbles in the flow regime corresponding to modulated Taylor vortex flow. Moreover, the gradient of the azimuthal velocity near the walls, source of the wall shear stress, decreases by 10%. The modified velocity distribution by adding microbubbles is comparable to that obtained with a 20% lower Reynolds number. Microbubbles in the coherent structure of the wavy Taylor vortices are visualized and exhibit a preferential distribution and motion at the crests and troughs of the waviness. The roles of the inhomogeneously distributed microbubbles in wavy vortical structures are discussed in view of our findings. (C) 2013 AIP Publishing LLC.
  • Tomoaki Watamura, Yuji Tasaka, Yuichi Murai
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 47 68 - 80 2013年05月 [査読有り][通常論文]
     
    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年05月 [査読有り][通常論文]
  • Effects of flaps and vortex generators on air entrainment by a hydrofoil bubble generator for drag reduction of ships
    KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji, OISHI Yoshihiko, SAKAMAKI Haruki, YAMAUCHI Hideaki, ISAHIKAWA Yutaro, EGASHIRA Ryu
    Proceedings of International Conference on Multiphase Flow 2013 (ICMF2013) #594 2013年05月 [査読有り][通常論文]
  • Xiaoshu Cai, Zhiyao Huang, Feng Dong, Yuichi Murai
    PARTICUOLOGY 11 2 134 - 134 2013年04月
  • T.Watamura, Y.Tasaka, Y.Murai
    Theoretical and Applied Mechanics Japan 61 2013年02月 [査読有り][通常論文]
  • Kosuke Sakurai, Yuji Tasaka, Yuichi Murai
    日本機械学会論文集 B編 79 797 1 - 11 2013年 [査読有り][通常論文]
     
    A new approach to deduce the effective viscosity of bubbly liquid with considering non-equilibrium bubble deformations in transient shear flows was proposed. Simultaneous measurement of the bubble shape and the spatio-temporal velocity distribution clarified that bubble deformation has delay from a variation of the local Capillary number under a transient process of flows from a stationary state to a rigid body rotation (spin-up) in a rotating cylinder. Relative viscosity of the bubbly liquid against the single phase condition estimated by the proposed method shows 60 % increase as the maximum. Such large increase of the effective viscosity cannot be introduced by mixture of spherical bubbles and bubbles with equilibrium deformations, and thus the non-equilibrium bubble deformations take a primary role on the modification of the effective viscosity in unsteady shear flows. © 2013 The Japan Society of Mechanical Engineers.
  • 桜井 康介, 田坂 裕司, 村井 祐一
    日本機械学会論文集 B編 79 798 227 - 227 The Japan Society of Mechanical Engineers 2013年 
    式にフォントが乱れているものがございましたので，修正させていただきます．
  • Atsuhide Kitagawa, Takuya Ozato, Yuichi Murai
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 79 800 701 - 711 2013年 [査読有り][通常論文]
     
    This paper presents an experimental investigation of motion characteristics of microbubbles rising close to a vertical plane wall. The study focuses on how microbubble behaviors change with the bubble diameter and along the wall for a constant bubble flow rate. Tap water is used as the working fluid, and hydrogen microbubbles are generated by water electrolysis. A particle tracking velocimetry technique is used to precisely measure the microbubble velocity, with which we found that the mean rise velocity of microbubbles is much faster than theoretically estimated rise velocity of single microbubble in stationary water. The mean bubble rise velocity increases with the bubble diameter and decreases in the downstream direction, and both are related to the balance between accumulation and diffusion of spatial buoyancy distribution near the wall. In particular, in the case of small microbubbles, bubble clouds are generated close to the wall and show intermittent roll-up motion in the wall-perpendicular direction (void burst motion). We discussed on this motion with various waveforms of the bubble rise velocity and bubble-bubble distance. ©2013 The Japan Society of Mechanical Engineers.
  • マイクロバブルの導入による水平混合層の局所乱流スペクトル変形
    渡村友昭, 田坂裕司, 村井祐一
    日本混相流学会論文集 27 5 521 - 530 2013年 [査読有り][通常論文]
  • 北浦秀和, 村井祐一, 田坂裕司, 熊谷一郎, 城野清司
    日本機械学会論文集B編 79 801 966 - 979 The Japan Society of Mechanical Engineers 2013年 [査読有り][通常論文]
     
    Fluid dynamic process of density destratification enabled by a bubble plume is investigated. General parametric dependence to global mixing is studied with numerical simulation coded by number density model of bubbly flow and then multiple experiments using dye visualization and ultrasonic velocity profiling (UVP) are carried out to find out the spatiotemporal structure of the two-phase flow emerging during destratification. The results show that intermittent convection driven in the near field of the bubble plume plays the primary role of the destratification. The intermittency is triggered by interaction between the near-field turbulence and the far-field wavy motion of bubble plume, which is clearly shown by the recurrence map and the power spectra of the velocity fluctuation measured by UVP.
  • シリコンオイルによる水平チャネル内気泡流の摩擦抵抗特性（第2報 壁面せん断応力の時間変動解析）
    大石義彦, 村井祐一, 田坂裕司
    混相流 28 1 81 - 89 2013年 [査読有り][通常論文]
  • シリコンオイルによる水平チャネル内気泡流の摩擦抵抗特性（第1報 摩擦抵抗計測とゲイン評価）
    大石義彦, 村井祐一, 田坂裕司
    混相流 28 1 71 - 80 2013年 [査読有り][通常論文]
  • 熊谷 一郎, 大薮 剛志, 田坂 裕司, 村井 祐一
    混相流 25 5 399 - 406 2012年08月 [査読有り][通常論文]
  • 村井 祐一, 田坂 裕司, 大石 義彦
    可視化情報学会誌 = Journal of the Visualization Society of Japan 32 126 19 - 22 The Visualization Society of Japan 2012年07月01日 
    水平チャネル流路に観察される気液二相流について紹介する．このテーマは特に乱流摩擦抵抗低減技術における基礎的物理メカニズムの解明において関心がもたれている．著者らはシリコンオイルによる気液界面の不純物影響を除去した実験や，水―空気系の高レイノルズ数条件での気液界面や液相乱流構造の可視化実験を行った．その結果，レイノルズ数が低く層流の場合は気泡群がスパン方向に配列し，乱流遷移したあとは主流方向に筋状模様をなすクラスタリングを見せた．また，このような気泡数密度の疎密波はボイド率の変動として観測され，それが大きい場合のほうが壁面摩擦抵抗の時間平均値が低下することがわかった．すなわち気泡による抵抗低減では，ボイド率の変動は邪魔なものではなく，むしろ歓迎されるべき現象である．この知見をもとに人工的にボイド率を変動させる実験を行うなど実験研究が展開を見せている．
  • 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年06月 [査読有り][通常論文]
  • Ichiro Kumagai, Koji Oyabu, Takafumi Kushida, Yuichi Murai, Yuji Tasaka, Yoshiaki Takahashi
    日本機械学会論文集 B編 78 787 500 - 503 2012年 [査読有り][通常論文]
     
    We have invented a new power-saving device for ship drag reduction using microbubbles in order to reduce CO 2 emissions from ships. The new device, which consists of angled hydrofoils with air introducers, has been installed on a coaster and helps achieving ∼10% net power saving. This device utilizes a low-pressure region produced above the hydrofoil as the ship moves forward, which drives atmospheric air into the water. Emissions can be reduced by about 87 million CO 2 ton/year if international shipping uses this new device, with 10% net-power reduction. We present the principal and optimization of this device on the basis of laboratory experiments on hydrofoils moving close to a free surface. In particular, we discuss free surface deformation and entrainment process using hydrofoils. © 2012 The Japan Society of Mechanical Engineers.
  • Atsuhide Kitagawa, Kazuaki Yamamoto, Yuichi Mural
    日本機械学会論文集 B編, 78 793 1539 - 1549 2012年 [査読有り][通常論文]
     
    This paper describes effects of microbubble injection on natural convection heat transfer from a vertical heated plate in water. Thermocouples are used for the temperature measurement and an image processing technique is used for obtaining the bubble diameter, the bubble velocity and the bubble layer thickness. The working fluid used is tap water. and li drogcn bubbles generated b electrolysis of the water are used as the inicrobubbles. For a constant bubble flow rate and a constant wall heat flux, in the laminar and transition regions. the heat transfer coefficient is significantly increased by the microbubble injection (The ratio of the heat transfer coefficient with bubble injection to that without injection is I .6-2.0 in both regions). The heat transfer enhancement in the laminar region results from both the forced-cons cction and mixing effects due to microbubbic injection. On the other hand, the heat transfer cnhaiemncnt in the transition region is iiiainlv affected b' acceleration of the transition to turbulence due to microbubblc injection. © 2012 The Japan Society of Mechanical Engineers.
  • Hideki Murakawa, Tatsuya Kawaguchi, Hironari Obayashi, Yuichi Murai, Yuji Tasaka
    Fluid Mechanics and its Applications 101 227 - 262 2012年 [査読有り][通常論文]
     
    We have many demands to understand flow phenomena in many industrial applications. Detecting the gas-liquid interface is important when measuring velocities in two-phase flow or in an open channel. We want to obtain velocity distributions two dimensionally, also. To extend the applicability, many techniques utilizing the ultrasonic Doppler velocity profiler (UVP) have been recently developed. This chapter shows these extended techniques. Liquid and gas velocity distributions are obtained simultaneously using a multi-wave transducer are described in Sect. 7.1. Techniques detecting a gas-liquid interface depending on fluid interface relative to the ultrasonic wavelength are presented in Sect. 7.2. The UVP is utilized for measuring void fraction distributions in Sect. 7.3. Section 7.4 shows a technique measuring two-dimensional velocity components. A new approach for improving temporal resolution using the ultrasonic correlation method is presented in Sect. 7.5.
  • Yuichi Murai, Noriyuki Furuichi, Yasushi Takeda, Yuji Tasaka
    Fluid Mechanics and its Applications 101 71 - 103 2012年 [査読有り][通常論文]
     
    On the basic of the ultrasonic principle made clear in Chaps. 1- flow velocity profiling can be realized if the Doppler method is applicable to the flow system. There are standard velocity fields, which are the most appropriate systems for examining the performance of ultrasonic velocity profiling (UVP) and training users in making UVP measurements. The standard velocity fields have a one-dimensional one-component velocity distribution, irrespective of whether they are steady or unsteady, such as in the case of flow in a rotating circular cylinder and laminar flow in a pipe. Measuring flow in such systems helps clarify the functions of UVP subject to diverse practical problems. Once velocity information is acquired, it is suitably adjusted in post-processing. Post-processing has two purposes: one is to improve the data quality in response to the inclusion of noise in velocity data, and the other is to derive statistical and other quantities.
  • Yuji Tasaka, Beat Birkhofer, Noriyuki Furuichi, Hiroshige Kikura, Hisato Minagawa, Yuichi Murai, Hideki Murakawa, Masaaki Motozawa, Samsun Nahar, Hironari Obayashi, Tatsuo Sawada, A. K. Jeelani Shaik, Yasushi Takeda, Kenichi Tezuka, Yoshiyuki Tsuji, Takatoshi Yanagisawa, Sanehiro Wada, Johan Wiklund, Erich J. Windhab
    Fluid Mechanics and its Applications 101 107 - 200 2012年 [査読有り][通常論文]
     
    Because of the advantages of the ultrasonic velocity Doppler profiler (UVP), namely in spatiotemporal velocity field measurements and in its applicability for opaque liquids, UVP has a wide field of application in science and industry. The following chapter introduces carefully selected examples of applications covering relatively basic areas of application. The focus of the contents in this chapter is categorized into (1) studies of flow instability and transition (Sect. 5.1), (2) measurements and investigations of liquid metal flows (Sect. 5.2), (3) developments of new rheometry (Sect. 5.3), (4) determinations of rheological properties (Sect. 5.4), (5) studies of magnetic fluids (Sect. 5.5) and (6) gas-liquid two-phase flow (Sect. 5.6), (7) measurements of flowrate in turbidity flows (Sect. 5.7), and (8) -determinations of flows in a deforming tube for biomedical applications (Sect. 5.8). The measurement and post-processing techniques used in this chapter are described in detail in Chaps. 4 and 7, and, detailed explanations of these aspects are omitted in this chapter.
  • Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    7TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1428 2012年 [査読有り][通常論文]
     
    Ultrasound pulse Doppler method is applied for componential volumetric flow rate measurement in multiphase pipe flow consisted of gas and liquid phases. The flowmetering is realized with integration of measured velocity profile over the cross section of the pipe within liquid phase. Spatio-temporal position of interface is detected also with the same ultrasound pulse, which further gives cross sectional void fraction. A series of experimental demonstration was shown by applying this principle of measurement to air-water two-phase flow in a horizontal tube of 40 mm in diameter, of which void fraction ranges from 0 to 90% at superficial velocity from 0 to 15 m/s. The measurement accuracy is verified with a volumetric type flowmeter. We also analyze the accuracy of area integration of liquid velocity distribution for many different patterns of ultrasound measurement lines assigned on the cross section of the tube. The present method is also identified to be pulsation sensor of flow rate that fluctuates with complex gas-liquid interface behavior.
  • Koji Oyabu, Ichiro Kumagai, Yuji Tasaka, Yuichi Murai
    7TH INTERNATIONAL SYMPOSIUM ON MEASUREMENT TECHNIQUES FOR MULTIPHASE FLOWS 1428 2012年 [査読有り][通常論文]
     
    We have conducted laboratory experiments on the flow past a circular cylinder moving beneath an air-water interface. The vortex street and the free surface profile are visualized for Reynolds number between 200 and 15000 and for Froude number between 0.01 and 3.2. For the lower Reynolds number (Re <= 3000), the vortex shedding from a circular cylinder is suppressed by the free surface at the small gap ratio for Re<1000. As a result, the vortex structure becomes smaller and the frequency of eddy shedding decreases. At the higher Reynolds number (>10000), the surface deformation becomes substantial in the downstream of the cylinder and intermittent bubble injection by wave breaking is observed. In order to investigate the relationship between the frequency of the vortex shedding and the free-surface wave behavior, Lagrangian Frame PIV measurement is conducted. From the results of Strouhal-Reynolds number relationship for gap ratios between 0.25 and 2.0, the period of the vortex shedding becomes long when the gap ratio is small.
  • Ichiro KUMAGAI, Takafumi KUSHIDA, Koji OYABU, Yuji TASAKA, Yuichi MURAI
    Visualization of Mechanical Process 1 3 10.1615 /VisMechProc.v1.i3.120  2012年 [査読有り][通常論文]
  • 村井 祐一
    混相流 = Japanese journal of multiphase flow 25 3 237 - 244 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2011年09月15日 
    Particle image velocimetry and ultrasound velocity profiling have around 25 years in history from their first appearance on literature. The early type of their instruments measures flows only at very slow speed in simple spatial structure. The rapid advances in computing tip above silicon cycle escalated them onto the stage of wide applications from fundamental study in fluid mechanics to major experimental tool for designing, managing, and evaluating of thermo-fluid phenomena. Extension to multiphase flow in the last decade is making their big news both in science and engineering researches. This article reports on the current topics and technical problems in multiphase flow toward next generation.
  • Akinari Shigetomi, Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    RENEWABLE ENERGY 36 2 536 - 545 2011年02月 [査読有り][通常論文]
     
    The use of a Savonius type of vertical axis wind turbine is expanding in urban environments as a result of its ability to withstand turbulence as well as its relatively quiet operation. In the past, single turbine performance has been investigated primarily for determining the optimum blade configuration. In contrast, combining multiple Savonius turbines in the horizontal plane produces extra power in particular configurations. This results from the interaction between the two flow fields around individual turbines. To understand quantitatively the interaction mechanism, we measured the flow field around two Savonius turbines in close configurations using particle image velocimetry. The phase-averaged flow fields with respect to the rotation angle of the turbines revealed two types of power-improvement interactions. One comes from the Magnus effect that bends the main stream behind the turbine to provide additional rotation of the downstream turbine. The other is obtained from the periodic coupling of local flow between the two turbines, which is associated with vortex shedding and cyclic pressure fluctuations. Use of this knowledge will assist the design of packaged installations of multiple Savonius turbines. (c) 2010 Elsevier Ltd. All rights reserved.
  • Ichiro Kumagai, Yuichi Murai, Kei Kurita
    日本機械学会論文集 77 784 2236 - 2245 2011年 [査読有り][通常論文]
     
    The dynamics of melt migration in partially molten media has long been of interest in physical systems. In order to understand the spatio-temporal patterns of fluid transport in partially molten materials, we explored laboratory experiments on the behavior of viscous flow through deformable porous media. Our experiments were carried out in a transparent rectangular tank (2 × 20 × 18 cm) filled with deformable gel beads (poly acrylamide). A viscous fluid (sugar syrup-water mixture) was injected from a nozzle or a slit placed at the top of the tank. The viscosity and the flow rate of the injected fluid were varied (0.1∼11 Pa.s 0.05∼0.33 ml/s). We identified three types of fluid flow in the experiments: (1) homogeneous permeable flow, (2) pulsating flow, and (3) localized continuous plume flow. The transition from the homogeneous permeable flow to the localized fluidized flow depends on injection flow rate, viscosity of the fluid, and deformation behaviors of the porous media. The second type of the flow has a characteristic period equivalent to the pulsation interval. This pulsating phenomenon within the gel mixture is excited by the fluid motion of the injected fluid and is controlled by a self-adjustable hydrodynamic valve composed of deformable gel beads. © 2011 The Japan Society of Mechanical Engineers.
  • マイクロバブルプーム群の浮上成長に関する定量的可視化実験
    日本機械学会論文集 B77 88 - 97 2011年 [査読有り][通常論文]
  • KUMAGAI Ichiro, MURAI Yuichi, TASAKA Yuji, NAKAMURA Naoya
    JSME Journal of Fluid Science and Technology 6 6 2152 - 2159 The Japan Society of Mechanical Engineers 2011年 [査読有り][通常論文]
     
    Wave breaking and air bubble generation by a 2-D cylinder moving beneath a free surface were experimentally investigated. Measurements of the free surface profile and visualization of the air bubbles yield the threshold and the regime diagrams of the bubble generation, which depend on the cross-sectional shape of the cylinder, Reynolds number, effective Froude number, normalized depth of the cylinder and angle of attack. As the Reynolds and Froude numbers increase, the surface deformation becomes substantial in the downstream of the cylinder. A breaking wave with air entrainment occurs when the ratio of the wave height to the wave length is greater than ∼0.1. Our results provide useful information for design of facilities such as marine constructions and a hydrofoil air pump for drag reduction of ships.
  • Kotaro Takeshima, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 D 693 - 700 2011年 [査読有り][通常論文]
     
    Since Darrieus turbine is omnidirectional against the wind, it has a great essential advantage in turbulent wind environment. However, a disadvantage on the starting up is known in low velocity conditions of the wind compared with propeller turbines. Darrieus turbine has a low efficiency problem at low tip-speed ratios due to this disadvantage. Some studies have done to overcome this problem, but these have been on the beginning of the way toward the solution. The reason is that the angle of attack for Darrieus blades is changed largely during the rotation relative to the wind direction. In this study, we found a new technique to improve the efficiency. The technique is the providing a large internal cylinder rotating together with the blades, which can control the angle of attack of the blades. We evaluated the influence of cylindrical diameter on the blade performance by the time-averaged velocity distribution and the intensity of the velocity fluctuation comparing between with cylinder and without cylinder. The flow field around the blades is measured with two kinds of instruments. One is Hot Wire Anemometer for analyzing temporal variations of flows, and the other is Particle Image Velocimetry for analyzing the spatial flow structure in detail. Angles of attack and lift coefficients are calculated from the measured relative velocity vector field. As a result, the angles of attack and the lift coefficients are improved in some rotational angles, which are also confirmed by numerical simulations. Copyright © 2011 by ASME.
  • Ryuta Abe, Yuji Tasaka, Ichiro Kumagai, Yuichi Murai, Takatoshi Yanagisawa
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 D 2717 - 2722 2011年 [査読有り][通常論文]
     
    Internally heated convection is a fundamental phenomenon, largely governing the dynamics of natural systems such as the atmosphere and Earth's mantle. It also plays an important role in industrial applications. Here we have investigated the separation of the top thermal boundary layer in order to understand the cell enlargement and the dynamics of the cell pattern formation. To observe the development of the thermal boundary layer non-invasively, the temperature distribution of the vertical plane in a convective cell was visualized by particle image thermometry (PIT). Micro-encapsulated thermo-chromic liquid crystals (TLCs) were seeded in the test fluid and illuminated by a white light sheet, and scattering light was taken by a digital camera. For quantitative temperature measurement, we have calibrated the temperature changes with the variation of the hue color component. The development of the thermal boundary layer with respect to the Rayleigh number has been investigated. The results show the local Rayleigh number determined from the thickness of the thermal boundary layer, which increases towards a critical local Rayleigh number ∼600. Copyright © 2011 by ASME.
  • Takahisa Shiratori, Yuji Tasaka, Yuichi Murai, Kazuya Oyama, Ichiro Kumagai, Yasushi Takeda
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 D 2657 - 2662 2011年 [査読有り][通常論文]
     
    Velocity vector fields around a falling sphere in a 1.0 wt % polyacrylamide (PAA) solution are obtained on a vertical cross section by particle image velocimetry (PIV). PAA solution is known as non-Newtonian fluid, which has shear thinning and viscoelastic property. Strain rate tensor fields and deformation fields are calculated from the velocity vector fields in order to visualize the dynamic behavior of the fluid quantitatively. In velocity vector field, two typical flow regions are observed in the wake of the sphere: approaching flow to the sphere, rising flow called "negative wake" [1]. Results show that the strain rate tensor field gives fluid strain at the approaching flow region and the edge of the negative wake. Furthermore deformation history of one portion of the fluid shows that fluid is strained in the approaching flow region, and the strain rate at the edge of the negative wake represents their recovery to the original status of the fluid in the moving frame. Copyright © 2011 by ASME.
  • Yoshihito Miyagishima, Tomoaki Watamura, Yuji Tasaka, Yuichi Murai
    ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 1 D 2669 - 2675 2011年 [査読有り][通常論文]
     
    This study aims to clarify the self-organized structure of microbubble plume as a result of two-way interaction between microbubbles and a flow of the surrounding liquid medium. We observed a sequence on a development of microbubble plumes in a thin fluid layer. Here the microbubbles show accumulation pattern with a different wavenumber depending on the height in the vessel. Variation of spatial wavenumber in the developing process was determined from visualization images, and three areas were distinguished in this process (1) the area of rising microbubbles with a large wavenumber in a horizontal direction without time dependence (2) the area of forming a large-scale flow structure, called 'microbubble plume' here, which keeps the primary information, horizontal wavenumber of the bubble accumulation with a large wavenumber (3) the area where the microbubble distribution takes a smaller wavenumber and makes vertical accumulation pattern inside the bubbly flow that is due to the mutual interaction between rising microbubbles and a flow induced by bubbles. To clarify these mutual interactions between liquid and gas phases, we visualized fluid motion of the liquid phase around the microbubble plumes by laser induced fluorescence, LIF. In this way, swaying motions on the tip of rising up bubble plume and liquid phase entrainment into the bubble plumes were visualized. We found the mechanisms for the creation of the self-organized distribution of microbubbles in bubbly flows and its temporal change as the result of the interaction between gas and liquid phase motions in bubbly flows. Copyright © 2011 by ASME.
  • Yoshihito Miyagishima, Tomoaki Watamura, Yuji Tasaka, Ichiro Kumagai, Yuichi Murai
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 77 784 2306 - 2315 2011年 [査読有り][通常論文]
     
    The evolution of a plume formed by ascending micro-bubbles is investigated by using quantitative visualization to understand the elementary processes that contribute to the inverse energy cascade as small scale flow grows to a large convective flow process. To make the visualization manageable, the plume is confined between two close parallel plates so that the plume-driven convection is restricted to two-dimensions. The results indicate that the bubble plume self-organizes, with a negative diffusion coefficient of buoyancy distribution. A mechanism for the enlargement of the plume is given in terms of two-dimensional flow interaction with the liquid phase. It is confirmed that the kinetic energy is concentrated in the low wavenumber flow from the energy spectra of the liquid phase. © 2011 The Japan Society of Mechanical Engineers.
  • 宮城島 圭人, 渡村 友昭, 田坂 裕司, 熊谷 一郎, 村井 祐一
    日本機械学会論文集Ｂ編 77 784 2306 - 2315 一般社団法人 日本機械学会 2011年 [査読無し][通常論文]
     
    The evolution of a plume formed by ascending micro-bubbles is investigated by using quantitative visualization to understand the elementary processes that contribute to the inverse energy cascade as small scale flow grows to a large convective flow process. To make the visualization manageable, the plume is confined between two close parallel plates so that the plume-driven convection is restricted to two-dimensions. The results indicate that the bubble plume self-organizes, with a negative diffusion coefficient of buoyancy distribution. A mechanism for the enlargement of the plume is given...
  • Miyuki Yamada, Yuichi Murai
    JOURNAL OF VISUALIZATION 13 4 355 - 363 2010年11月 [査読有り][通常論文]
     
    A stereoscopic method of identifying story patterns in literary works is newly developed. The pattern is extracted from textual information by the detection of thematically assigned keywords, and depicted as visual imageries. The applicability of the method is demonstrated in several of Shakespeare's plays. The complex scenario patterns in Shakespeare's tragedies are successfully captured with applying the method for two different themes in each play. As the result, the organization of story accompanying multiple themes in a single play has been obtained as a pair of visual imageries, i.e. stereoscopic story visualization. This approach, in combination with a quadrant analysis of the plots, allows us in interpretation further complexity of human psychology in the characters and scene-by-scene transitions in each play.
  • Yuichi Murai, Yuji Tasaka, Yuichi Nambu, Yasushi Takeda, S. Roberto Gonzalez A
    FLOW MEASUREMENT AND INSTRUMENTATION 21 3 356 - 366 2010年09月 [査読有り][通常論文]
     
    Ultrasound reflects strongly off the gas-liquid interface when there is a large change in acoustic impedance. We exploit this phenomenon to detect the instantaneous position of the interface from the time of flight of pulsed ultrasound. Because the characteristics of the reflected wave depend on the shape and size of the interface relative to the ultrasound wavelength, the single-sensing principle is insufficient to capture the interface for generalized gas-liquid two-phase flows. In the present study, we design and examine three types of ultrasound interface detection techniques: the echo intensity technique, the local Doppler technique, and the velocity-variance technique, and investigate and compare the merits and limitations of each. The results indicate that the echo intensity technique is appropriate for turbulent interfaces that cause ultrasound scattering over wide angles. In contrast, the local Doppler technique is required to capture information from waves reflected from smooth interfaces and bubbles. Finally, we find that the velocity-variance technique works for quasi-steady and periodical two-phase flow, and we apply this technique to horizontal slug flow in a tube. (C) 2010 Elsevier Ltd. All rights reserved.
  • Jumpei Takahashi, Yuji Tasaka, Yuichi Murai, Yasushi Takeda, Takatoshi Yanagisawa
    INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 53 7-8 1483 - 1490 2010年03月 [査読有り][通常論文]
     
    This study determines the flow structure in a convection cell with an internally heated layer by PIV to elucidate the convection cell transition mechanisms. The vertical velocity component is determined and the cell behaviour with respect to Rayleigh number is investigated quantitatively. Cell expansion process is described as a consequence of development of the descending flow at the centre of cells. The results suggest that a spoke-like structure is stable in this system in ideal conditions and a double-cell structure is formed when there are restrictions on the system, i.e. finite lateral boundaries. (C) 2009 Elsevier Ltd. All rights reserved.
  • Shuhei Fujimoto, Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    JOURNAL OF VISUALIZATION 13 1 17 - 23 2010年02月 [査読有り][通常論文]
     
    Interfacial waves of two immiscible layers in a spin-up container were investigated using experimental visualization. While the interface near the central part rose up, instability waves propagated in an azimuthal direction on the interface. These waves were mainly caused by Kelvin-Helmholtz instability for the velocity difference between two layers during spin-up, but had complicated transient characteristics owing to the rotation in a closed system. We visualized the structure of the interfacial waves by the use of three types of optical characteristics of the interface. Image processing provided the detailed factors of the interfacial waves that were classified in four life stages from their generation to disappearance. The initial generation process involved many frequency modes due to a large velocity difference, and then a low mode stood out during the growth, and disappeared with an ellipsoidal sloshing mode to achieve the rigid rotation in both layers.
  • Tomoaki Watamura, Yuji Tasaka, Yuichi Murai, Yasushi Takeda
    日本機械学会論文集 B編 76 772 2160 - 2167 2010年 [査読有り][通常論文]
     
    We investigated the interaction between microbubbles and Taylor-vortices, which are generated in a fluid layer between coaxial-rotating double cylinders. O (10 μm) -diameter hydrogen bubbles were generated by water electrolysis and dispersed into the fluid layer. The maximum void fraction, which is estimated by the input power for the water electrolysis, was smaller than 0.02%. From the time averaged velocity distribution, which is observed by Ultrasonic Velocity Profiling (UVP), these values are changed with different tendency at Re/Re c = 3.0 or 4.0, where Rec is the critical Reynolds number for onset of the primary instability. As initially expected, the existence of the microbubbles does not modify the axial wavelength of the vortices and the frequency of the azimuthal waves either. However, the power of the modulation wave component, which comes from the flow instability, is lowered by the addition of microbubbles at Re/Rec = 8.0 This phenomenon is caused by the rising bubbles with the pattern, which makes inhomogeneous local void fraction.
  • Ichiro Kumagai, Yuichi Murai, Yuji Tasaka, Naoya Nakamura
    日本機械学会論文集 B編 76 772 2152 - 2159 2010年 [査読有り][通常論文]
     
    We have conducted laboratory experiments on air-bubble generation by a submerged twodimensional body moving at a constant velocity U0 in order to understand the fundamental flow physics of marine constructions such as pipe lines close to the air-water interface. Measurements of the free surface profile and visualization of the air bubbles yield the threshold and the regime diagrams of the bubble generation, which are described by cross-sectional shape of the cylinders, Reynolds number (Red= U0d/v, where d and v are the vertical thickness of the cylinders and kinematic viscosity of the water, respectively), Froude number (Frh= U0/(gh) 1/2, where h is the depth of the cylinders), and normalized depth of the cylinder (a = h/d). For circular cylinders, as Red and Fr h numbers increase, the surface deformation becomes substantial in the downstream of the cylinder and breaking wave with air entrainment occurs. The bubble generation by the breaking wave is also observed in the case of the elliptic cylinder although the condition of the bubble generation in the Re d-Frh regime diagram is different from that observed in the case of the circular cylinder. In any cases of the cylinders, the ratio of the wave height to the wave length, which should be the physical criterion of the breaking wave with bubble generation, is about 0.1.
  • Hidekazu Kitaura, Yuichi Murai, Yasushi Takeda, Peter J. Thomas
    日本機械学会論文集 B編 76 772 2143 - 2151 2010年 [査読有り][通常論文]
     
    Ultrasound Velocity Profiler (UVP) is applied to measurement of two-dimensional velocity vector field of vortex rings in water. The instantaneous flow field passing through the measurement section is reconstructed from spatio-temporal distribution of velocity component obtained along two different ultrasound measurement lines. The method of reconstruction is valid when vortex rings have axisymmetric structure having constant translational velocity at the measurement section. Using this principle, vortex ring subject to background rotation is also presented to discuss the effect of weak Coriolis force on formation process of vortex rings.
  • Yuichi Murai, Yuji Tasaka, Daiki Tanaka, Yasushi Takeda, Hirotaka Takeuchi
    日本機械学会論文集 B編 76 765 747 - 754 2010年 [査読有り][通常論文]
     
    Wake structure of permeable object is one of great concerns for wind engineering, chemical processing, and fluid machineries. It produces the drag greater than the same-sized solid object due to friction dominant nature even at Reynolds numbers higher than 10s. In order to characterize the wake structure in such a condition, we measure the flow field around the permeable cylinder made of wire mesh and annularly arrayed thin cylinders. The parametric study presents a spatially delayed amplification of turbulence due to vortex shedding in two frequencies compound in the wake. We also measure the flow for a rotating permeable cylinder to find the interaction between circulating elements and macroscopic behavior of flow. The result indicates a curtain effect of the elements to expand the momentum loss region behind the rotating cylinder.
  • Yuichi Murai, Ichiro Kumagai, Yuji Tasaka, Yasushi Takeda, Yoshiaki Takahashi
    日本機械学会論文集 B編 76 763 483 - 485 2010年 [査読有り][通常論文]
     
    Installation of hydrofoils to ship wetted surface enables bubble generation to be realized with power consumption much lower than conventional bubble generators. With help of this principle, net effect of frictional drag reduction for ships can be improved. We have already obtained around 10% net power-saving efficiency for a cargo ferry throughout about half a year. The power-saving has a large potential to be improved more by considering multiphase fluid dynamics in terms of the hydrofoil-water-air triple interaction. This paper presents the principle of the bubble generation, the estimation of net power-saving, and the flow structure visualized by experimental and numerical approaches.
  • Akinari Shigetomi, Yuichi Murai, Yuji Tasaka, Yasushi Takeda
    日本機械学会論文集 76 763 366 - 368 2010年 [査読有り][通常論文]
     
    Wind tunnel experiments are conducted to explore the flow field around two widely spaced Savonius windmills that interact to each other. The flow visualization with single and two arranged windmills is conducted with Particle Image Velocimetry (PIV). The mean and the fluctuation velocities are evaluated from PIV so that the interaction mechanism between two windmills is classified into the mean and the turbulent components. The best arrangement of two windmills is found to be a coupling of them with counter rotation at an inclined angle to the main flow. The pressure distribution on the best coupling condition is obtained by the data analysis of PIV, which indicates how the pressure field interferes positively to promote the rotations. From the present finding both for one-way and two-way interactions, the phase optimization for blades of each windmill is suggested for further promotion of the power-increasing interaction.
  • Tomoaki Takeuchi, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 21 1 1 - 10 2010年01月 [査読有り][通常論文]
     
    We investigate the tracer gas pulse injection method for flowmetering of natural gas pipelines. The principle of the measurement consists of detecting the passage of the pulse at two locations along the pipeline, from which the time of passage is calculated. The measurement accuracy depends on how the pulse form evolves due to turbulent diffusion and convective distortion in the pipe, as well as due to the influence of bends. We discuss these factors to evaluate the applicability of the method to pipelines of kilometer distances. We also perform a three-dimensional numerical analysis to understand the spatial pulse dispersion, and numerical analysis shows that the influence of pipe bends was not significant. Both experimental and theoretical results indicate the existence of axial diffusion coefficients, even in pipelines with bends. These results enable us to predict the evolution of the pulse concentration profile. Finally, we demonstrate acceptable precision for practical flowmetering applications in actual utility pipelines.
  • じゃむしどにあ はみどれざ, Tasaka Yuji, Murai Yuichi, Takeda Yasuhsi
    年次大会講演論文集 2010 181 - 182 一般社団法人日本機械学会 2010年 
    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.
  • 村井 祐一
    年次大会講演論文集 2010 121 - 122 一般社団法人日本機械学会 2010年 
    Ultrasound velocity profiling obtains 1-D 1-C flow velocity distribution from a single ultrasound transducer, and is suitable for monitoring one-component dominant flow field such as in pipes. Instead, two-dimensional flow structure such as vortex cannot be directly observed. This note reports several trials done by the author in terms of two-dimensional flow field reconstruction that is classified into three flow confifurations; transverse, rotational, and outward measurements.
  • W. H. Liu, T. Wan, W. Cheng, Yuichi Murai
    6TH INTERNATIONAL SYMPOSIUM ON MULTIPHASE FLOW, HEAT MASS TRANSFER AND ENERGY CONVERSION 1207 646 - + 2010年 [査読有り][通常論文]
     
    The flow pattern of gas-liquid two-phase flow in an aeration tank is of critical effect upon mass transfer by the convection. Bubble plume provides unsteadily fluctuating two-phase flow during the aeration. This paper the study on the unsteady structure of bubble plume is dealt with from experiment. The time-serial bubble plume images of different cases in tank have been analyzed. The RCC-PIV has been employed to calculate the velocities in those cases, and then the time-serial vortex, the total turbulence intensity, the time-serial streamline are obtained. It has been shown that the aspect ratio and void fraction are the dominant factors influencing the unsteady structure of bubble plume. When the aspect ratio is unity and the void fraction gets higher, the bubble plume has symmetrical vortex structure and longest residence time, which is beneficial for optimizing the aeration system and enhancing the applied range of bubble plume.
  • Yuichi MURAI, Yuji TASAKA, Yuichi NAMBU, Yasushi TAKEDA, S. Roberto, GONZALEZ A
    Flow Meas. Inst. 21 3 356 - 366 2010年 [査読有り][通常論文]
  • Koji Okamoto, Yuichi Murai
    MEASUREMENT SCIENCE AND TECHNOLOGY 20 11 2009年11月 [査読無し][通常論文]
  • Yuichi Murai, Shoko Ohta, Akinari Shigetomi, Yuji Tasaka, Yasushi Takeda
    MEASUREMENT SCIENCE AND TECHNOLOGY 20 11 114003  2009年11月 [査読有り][通常論文]
     
    A method for measuring the spatial distribution of the void fraction in bubbly two-phase flow is presented. The method is referred to as ultrasonic void fraction profiling since it is based on the signal processing of an ultrasonic pulse scattering on a bubble interface. The method is established using two processes for the ultrasonic sensing of bubbles. One approach is to detect the bubble interface along a measurement line, i.e. the path of the ultrasonic pulse in the liquid. The interface is captured using two types of signal-processing schemes: the echo intensity method and the Doppler method. The other approach is to reconstruct the void fraction profile from the number of bubble interfaces. A theoretical formula for the estimation is proposed by considering ultrasonic reflection in a suspension of bubbles. The validity of the formula is examined with theoretical and numerical bases. Finally, the method developed here is applied to four flow configurations for the demonstration, in which the void fraction profile governs the modulation of liquid flow field.
  • H.J. Park, Y. Oishi, Y. Tasaka, Y. Murai, Y. Takeda
    Journal of Physics: Conference Series 147 12037 012037 - 13 2009年03月 [査読有り][通常論文]
  • Huang Jian, Murai Yuichi, Yamamoto Fujio
    JOURNAL OF HYDRODYNAMICS 21 1 93 - 99 2009年02月 [査読有り][通常論文]
     
    Our previous Study showed that the frictional drag decreases with increasing void fraction at Re > 1300, while it increases at Re < 1000. Decomposition of the Reynolds shear stress also implied that bubbles induce isotropy of turbulence. In order to confirm our previous analysis and to further investigate flow fields in the vicinity of bubbles, we analyze velocity fluctuations on the quadrant space in the streamwise and transverse directions (u'-v' plane). Here, we focus oil two specific Reynolds numbers (at Re approximate to 900 and approximate to 14 10, which are close to the laminar-to-turbulent transition regime) and discuss bubble effects on sweep (u'>0, v'<0) and ejection (u'<0, v'>0) events as a function of the Reynolds number. We also illustrate velocity fluctuations in the vicinity of all individual bubble and a swarm of bubbles oil the u'-v' coordinates. The results show that a bubble swarm suppresses the velocity fluctuations at Re approximate to 1410.
  • J. Huang, T. Suzuki, Y. Murai, F. Yamamoto
    Journal of Physics: Conference Series 147 2009年 
    Our previous study showed that the frictional drag decreases with increasing void fraction at Re > 1300, while it increases at Re < 1000. Decomposition of the Reynolds shear stress also implied that bubbles induce isotropy of turbulence. In order to confirm our previous analysis and to further investigate flow fields in the vicinity of bubbles, we analyze velocity fluctuations on the quadrant space in the streamwise and transverse direction (u' - v' plane). Here, we focus on two specific Reynolds numbers (at Re 900 and 1410, which are close to the laminar-to-turbulent transition region) and discuss bubble effects on the sweep (u' > 0, v' < 0) and ejection (u' < 0, v' > 0) events as a function of the Reynolds number. We also illustrate the velocity fluctuations in the vicinity of an individual bubble and a swarm of bubbles on the u' - v' coordinates. The result shows that a bubble swarm suppresses the velocity fluctuations at Re 1410. We then rearrange the scatted PTV vectors and compute power spectra of the kinematic energy of each velocity component. It only indicates that the elongated bubble suppresses low frequency Ew at Re 1410. © 2009 IOP Publishing Ltd.
  • Visualization of transient interfacial waves induced by spin-up of two immiscible fluid layers
    Journal of Visualization 10 1007  2009年 [査読有り][通常論文]
  • S. Roberto Gonzalez A, Yuichi Murai, Yasushi Takeda
    Advances in Chemical Engineering 37 1 - 27 2009年 [査読有り][通常論文]
     
    Ultrasonic velocity profiler (UVP) measurements are performed for gas-liquid two-phase flow. The UVP measurements are conducted in a rectangular channel and in a pipe, both horizontally oriented. The liquid velocity measurements and ultrasound echo intensity are used to locate the position of the gas-liquid interface information. Liquid velocity data are analyzed to obtain the bubble interface for the study of the mechanism of drag reduction. The peak ultrasound echo intensity is used to locate the position of the gas-liquid interface in a pipe for the estimation of the liquid flow rate. No gas-flow rate calculations are performed. The experiments in the pipe are performed using three UVP-DUO systems simultaneously to obtain a more accurate shape for the gas-liquid interface. The tests conducted belong to three different flow regimes: stratified, elongated bubble, and slug flow. The results show very good agreement with the actual liquid flow rates. © 2009 Elsevier Inc. All rights reserved.
  • Tetsushi Kanda, Yuichi Murai, Yuji Tasaka, Yasushi Takeda, Hideaki Tezuka, Michitsugu Mori
    日本機械学会論文集 75 751 561 - 563 2009年 [査読有り][通常論文]
     
    The present study aims at developing a 3-D trajectory measurement system for birds, in particular for endangered species, e.g. raptorial, flying around wind turbines as a part of its complete system to be applied for prevention from bird strike. The method is based on stereoscopic photography, which is similar to 3-D particle tracking velocimetry. For stabilizing the bird-image detection performance in natural background, the time differential technique is proposed and examined considering constraint of time of day and weather on the measurement. All tests are conducted in outdoor farm. For the demonstration purpose, 3-D trajectories of crows flying above the farm are obtained and shown in order to assess the effectiveness of stereoscopic photography for live birds.
  • Shoko Ohta, Akinari Shigetomi, Yuji Tasaka, Yuichi Murai, Yasushi Takeda, Munehiko Hinatsu
    日本機械学会論文集 75 751 538 - 540 2009年 [査読有り][通常論文]
     
    Friction drag accounts for 80% of the total drag for large ships, and drag reduction realized by injecting air bubbles is expected as one of the feasible ways because of less environmental impact. We have measured the turbulent boundary layer structure altered by bubbles beneath 127 m-ship by means of ultrasonic Doppler velocimetry. This short paper mainly describes the measurement method of seawater velocity profiles and the some typical results on the influences of bubbles.
  • M. Yamada, Y. Murai
    Journal of Visualization 12 2 181 - 188 2009年 [査読有り][通常論文]
     
    With the rapid advance in information technology, the applicability of computers has moved from the scientific field towards simulating human intelligence. We are already familiar with using computers to produce music and art and for language translation. A further use is in understanding traditional man-made products; best exemplified by literary works. In this study, we focus on enabling a computer to visualize the meaning of stories. Four world-famous plays by William Shakespeare have been chosen to demonstrate how the visualization scheme works in grasping the meaning of the stories. The scheme employs primitive keyword detection and ellipsoidal differential equations to create a visual imagery of the story. This methodology ensures uniqueness in the visualization of an individual work. In addition, color palettes obtained from pictures relevant to each story are used to enrich the consistency between the visual sense and the meaning of the story.
  • 藤本 修平, 村井 祐一, 田坂 裕司, 熊谷 一郎, 武田 靖
    年次大会講演論文集 2009 89 - 90 一般社団法人日本機械学会 2009年 
    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.
  • 村井 祐一, 古田 功治, 田坂 裕司, 武田 靖
    年次大会講演論文集 2009 63 - 64 一般社団法人日本機械学会 2009年 
    Vortex patterns in Taylor-Couette flow are uniquely determined with Reynolds number in single-phase medium. It never contains hysteresis in any transition from one to another for sufficiently large aspect ratio. In contrast, inclusion of bubbles provides a remarkable hysteresis in wavy vortex regime, snowing a periodic switching between spiral and toroidal modes. From this fact, space-time four-dimensional mechanism on bubble-vortex interaction is to be deduced from a number of physical aspects. Moreover, the interaction is tightly relevant to frictional drag reduction that occurs at high gain factor up to 10. We report on the interpretation on this phenomenon in this paper.
  • Y. Murai, M. Yamada
    JOURNAL OF VISUALIZATION 12 1 5 - 5 2009年 [査読有り][通常論文]
  • Takamasa SUZUKI, Yoshihiko OISHI, Yuichi MURAI, Yuji TASAKA, Yasushi TAKEDA
    J. Phys: Conference Series 147 012012  2009年 [査読有り][通常論文]
  • Koji YOSHIDA, Yuji TASAKA, Yuichi MURAI, Yasushi TAKEDA
    J. Phys: Conference Series 147 012013  2009年 [査読有り][通常論文]
  • 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年09月 [査読有り][通常論文]
  • Yuichi Murai, Hiroshi Oiwa
    FLUID DYNAMICS RESEARCH 40 7-8 565 - 575 2008年07月 [査読有り][通常論文]
     
    The effective viscosity of bubbly liquids is measured using the Stokes drag of a falling sphere, i.e. falling sphere viscometry. This method can evaluate the influence of a bubble's transient deformation. Viscosity relative to a single-phase fluid is directly obtained by the terminal falling velocities of the sphere. When bubbles are distributed around the sphere up to a void fraction of alpha, the following results are obtained. The relative viscosity for spherical bubble dispersion agrees with the Stokes-Einstein formula; 1 + alpha. For large capillary numbers, relative viscosity converges to approximately 1 - (5/3)alpha because bubble deformation is fully yielded. Between these two states, relative viscosity has a value higher than in simple shear flow. The critical capillary number is found to be 3.5, being five times as that of simple shear flow. The viscosity-increasing mechanism for trans-critical capillary numbers is deduced from the fact that bubbles have transient deformation along the streamline. (c) 2008 The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.
  • Jian Huang, Yuichi Murai, Fujio Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 19 2 93 - 105 2008年04月 [査読有り][通常論文]
     
    To investigate the effect of microbubble injection into a turbulent boundary layer, we measure the velocity fields of gas-liquid two-phase flow in a horizontal water channel with a Particle Tracking Velocimetry (PTV) technique. In this study, we focus on a thin shear layer where the Reynolds shear stress is the highest. The effect of the shallow focal depth-of-field (DOF) in a lens system assists to improve the spatial resolution of the PTV results. Considering the distribution of luminous flux, we first enhance the illumination intensity to label the objects on images. With their assistance together with an image processing filter, we can then improve the in-depth resolution of tracer particles and determine their positions more accurately. We apply this shallow DOF-based PTV technique to measure the streamwise and spanwise velocity components and visualize the motion of bubbles relative to continuous phase in the near-wall region at three downstream positions. The result shows that the averaged velocity right downstream of the bubble injector clearly decreases due to microbubbles. The local instantaneous flow structure around bubbles shows no clear coherence because of highly turbulent background; however, the frequency spectrum analysis finds that the bubbles reduce the kinetic energy in a frequency range higher than the bubble passing frequency. (C) 2008 Published by Elsevier Ltd.
  • Yuichi Murai, Hiroshi Oiwa, Yasushi Takeda
    PHYSICS OF FLUIDS 20 3 1 - 8 2008年03月 [査読有り][通常論文]
     
    Frictional drag reduction due to the presence of small bubbles is investigated experimentally using a Couette-Taylor flow system; i.e., shear flow between concentric cylinders. Torque and bubble behavior are measured as a function of Reynolds number up to Re = 5000 while air bubbles are injected constantly and rise through an array of vortical cells. Silicone oil is used to avoid the uncertain interfacial property of bubbles and to produce nearly monosized bubble distributions. The effect of drag reduction on sensitivity and power gain are assessed. The sensitivity exceeds unity at Re < 2000, proving that the effect of the reduction in drag is greater than that of the reduction in mixture density. This is due to the accumulation of bubbles toward the rotating inner cylinder, which is little affected by turbulence. The power gain, which is defined by the power saving from the drag reduction per the pumping power of bubble injection, has a maximum value of O (10) at higher Re numbers around 2500. An image processing measurement shows this is because of the disappearance of azimuthal waves when the organized bubble distribution transforms from toroidal to spiral modes. Moreover, the axial spacing of bubble clouds expands during the transition, which results in an effective reduction in the momentum exchange. (C) 2008 American Institute of Physics.
  • Y. Murai, Y. Oishi, Y. Tasaka, Y. Takeda
    JOURNAL OF VISUALIZATION 11 1 63 - 70 2008年01月 [査読有り][通常論文]
     
    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.
  • 古屋 直樹, 藤本 修平, 田坂 裕司, 村井 祐一, 武田 靖
    年次大会講演論文集 2008 93 - 94 一般社団法人日本機械学会 2008年 
    In this study, we aim to develop a scheme for estimating properties of viscoelastic liquid, by means of Ultrasonic Velocity Profiler (UVP). Unsteady velocity profiles of a visco-elastic fluid driven by sudden spin are measured with it to find out the behavior of the fluid motion as well as to assess the visco-elastic properties. The measurement result shows typical response due to the elastic property. In addition, we carried out numerical simulation of the transient flow based on Bingham model considering yield stress, to clarify the oscillatory behavior.
  • Yuuta NOMURA, Yuji TASAKA, Yuichi MURAI, Yasushi TAKEDA
    J. Phys: Conference Series 137 012001 - 6 2008年 [査読有り][通常論文]
  • Ultrasonic Doppler visualization of slug flow in a horizontal pipe
    S.R. Gonzales, Y.MURAI, Y.TASAK, Y.OISHI, Y.TAKEDA
    Proc. 13th International Symposium on Flow Visualization 2008年 [査読有り][通常論文]
  • 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年 [査読有り][通常論文]
  • Y.OISHI, Y.MURAI, Y.TASAKA, Y.TAKEDA
    Proc. 6th Intl. Sym. Measurement Tech. for Multiphase Flows 147 USB-proceedings, No. 5, Book o - 14 2008年 [査読有り][通常論文]
  • Yuichi Murai, Kazumasa Inaba, Yasushi Takeda, Fujio Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 18 5-6 223 - 229 2007年10月 [査読有り][通常論文]
     
    Backlight imaging tomography is used to experimentally investigate interfacial structures of gas-liquid two-phase flow in circular tubes. The tomography method is based on the attenuation of visible light that causes the inside of the liquid phases to be colored with dye. Increasing the number of light projections provides accurate phase distributions to be reconstructed by a linear backward projection scheme. After the reconstruction performance is examined with numerical simulations for several test cases, the method is applied to slug flows that have complicated 31) interfaces from turbulence. Interfacial structures are compared between straight and helical tubes to determine the effect of centrifugal acceleration. The result demonstrates that centrifugal acceleration provides a liquid-clinging layer on the inner wall against gravity while a high-speed collision of liquid with the top wall happens in a straight tube. (c) 2007 Elsevier Ltd. All rights reserved.
  • Yuichi Murai, Taishi Nakada, Takao Suzuki, Fujio Yamamoto
    MEASUREMENT SCIENCE AND TECHNOLOGY 18 8 2491 - 2503 2007年08月 [査読有り][通常論文]
     
    Particle tracking velocimetry (PTV) is applied to flows around a Savonius turbine. The velocity vector field measured with PTV is utilized to estimate the pressure field around the turbine, as well as to evaluate the torque performance. The main objective of the work is the establishment of the pressure estimation scheme required to discuss the turbine performance. First, the PTV data are interpolated on a regular grid with a fourth-order ellipsoidal differential equation to generate velocity vectors satisfying the third-order spatio-temporal continuity both in time and space. Second, the phase-averaged velocity vector information with respect to the turbine angle is substituted into three different types of pressure-estimating equations, i.e. the Poisson equation, the Navier-Stokes equation and the sub-grid scale model of turbulence. The results obtained based on the Navier-Stokes equation are compared with those based on the Poisson equation, and have shown several merits in employing the Navier-Stokes-based method for the PTV measurement. The method is applied to a rotating turbine with the tip-speed ratio of 0.5 to find the relationship between torque behaviour and flow structure in a phase-averaged sense. We have found that a flow attached to the convex surface of the blades induces low-pressure regions to drive the turbine, namely, the lift force helps the turbine blades to rotate even when the drag force is insufficient. Secondary mechanisms of torque generation are also discussed.
  • Motion of Microbubbles Relative to Streamwise Vortices in the Wall Turbulence
    Y.OISHI, Y.MURAI, Y.TASAKA, Y.TAKEDA
    Abstracts of the6th International Conference on Multiphase Flow S1_Wed_C_37, CD-ROM 55  2007年08月 [査読有り][通常論文]
  • Yuichi Murai, Hiroshi Fukuda, Yohiko Shi shi, Yoshiaki Kodama, Fujio Yamamoto
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 33 2 147 - 163 2007年02月 [査読有り][通常論文]
     
    Microbubble and air film methods are believed to be applicable to skin friction reduction in ships. Small bubbles are dispersed into the turbulent boundary layer in the former case, and wide air layers cover the wall surface in the latter case. Previous studies did not specifically address the intermediate case between the microbubble and air film conditions. This study is concerned with the possibility and mechanism of drag reduction using relatively large air bubbles compared to the boundary layer thickness in a horizontal turbulent channel flow. The relationship between local skin friction and the bubble's interfacial structure is investigated by synchronizing the measurement of wall-shear stress with the image acquisition of bubbles. The bubble sizes range from 2 to 90 mm approximately. As a result, a negative correlation between the local skin friction and the local void fraction is confirmed by the time-resolved measurement. A new observation is the fact that the local skin friction decreases drastically in the rear part of individual large bubbles, and rapidly increases after the bubble's rear interface passes. This characteristic underlies the bubble-size dependency of the average skin friction in the intermediate bubble size condition. (c) 2006 Elsevier Ltd. All rights reserved.
  • Wen Cheng, Chun-Di Yang, Yuichi Murai, Fujio Yamamoto
    AIP Conference Proceedings 914 453 - 457 2007年 
    Aeration plays an important role in the treatment of activated sludge. The aeration performance is deeply affected by the movement law of bubble liquid flow in aeration tank. In order to discuss the influence of gas-phase, liquid-phase motions in an aeration tank on the sewage disposal, three kinds of boundaries and initial conditions were applied in the experiment to study the law of two-phase flow. A developed two-equation turbulence model was employed in this paper. Results obtained by experiment are compared with those from the mathematical model. It is found that the results of measurement and simulation agree with each other. © 2007 American Institute of Physics.
  • Yoshihiko Oishi, Hiroshi Fukuda, Yuichi Murai
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 73 6 1298 - 1306 2007年 
    Flow field modified by a single large bubble in a horizontal wall turbulent boundary layer is measured by particle tracking velocimetry. We focus on intermediate bubble size being comparable to the thickness of boundary layer to find out the events altering the original turbulent shear stress field. The results are all presented by quantities relative to single-phase flow on Lagrangian coordinate that moves with the bubble. The measurement results reveal bubble-produced secondary flow around itself, which involves twin roll vortices, separation on the bubble surface, and strong sweeping flow. For a small and nearly spherical bubble, the sweeping flow is provided strongly to enhance the turbulent momentum exchange while negative exchange is detected for a large flat bubble. This effective length approximately corresponds to the vertical size of the bubble.
  • 村井 祐一, 田坂 裕司, 武田 靖, 石川 正明
    可視化情報学会誌 27 107 253 - 258_1 The Visualization Society of Japan 2007年
  • 神田 哲志, 田坂 裕司, 村井 祐一, 武田 靖
    可視化情報学会誌 27 2 91 - 92 The Visualization Society of Japan 2007年 
    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.
  • 矢野 可南子, 田坂 裕司, 村井 祐一, 武田 靖, 柳澤 孝寿
    可視化情報学会誌 27 1 271 - 272 The Visualization Society of Japan 2007年 
    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.
  • 神田 哲志, 村井 祐一, 田坂 裕司, 武田 靖
    可視化情報学会誌 27 1 161 - 162 The Visualization Society of Japan 2007年 
    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.
  • 村井 祐一, 大岩 浩司, 武田 靖
    可視化情報学会誌 27 1 129 - 130 The Visualization Society of Japan 2007年 
    Microbubble drag reduction in Taylor-Couette flow system is investigated experimentally. We measured torque acting on rotating inner cylinder and evaluated the power gain of the drag reduction as function of Reynolds number from 600 to 4, 500. The results have shown that the gain increased up to 20 in the case that the bubble distribution organized by Taylor cell was altered from toroidal to spiral structures. This range coincided with the fact that the wavelength of the bubble-cluster spacing was elongated due to bubble-to-vortex interaction.
  • 鈴木 隆政, 大石 義彦, 村井 祐一, 田坂 裕司, 武田 靖
    可視化情報学会誌 27 1 113 - 114 The Visualization Society of Japan 2007年 
    Longitudinal vortices sensitively govern the turbulent momentum transport in boundary layers. In order to obtain the fundamental knowledge on microbubble drag reduction mechanism, the interaction between the vortices and the bubbles are experimentally investigated in this study. The longitudinal vortex is generated artificially from a delta wing installed inside the shear layer in a channel. According to PTV measurement, the vorticity is reduced by presence of bubbles compared to the original. Significant displacement of the vortex core is also confirmed to explain the momentum transfer modification. Moreover, numerically simulated bubble trajectories on the measured velocity yields to high persistency of the interaction for small bubbles.
  • Tetsushi Kanda, Yuji Tasaka, Yuichi Murai, Yasushi Takeda
    FEDSM 2007: PROCEEDINGS OF THE 5TH JOINT AMSE/JSME FLUIDS ENGINEERING SUMMER CONFERENCE VOL 1, PTS A AND B 679 - 686 2007年 [査読有り][通常論文]
     
    Availability of particle tracking velocimetry (PTV) that is applied to movie images of soap bubbles in airflow is investigated experimentally. This study is positioned as a basic research for measuring environmental flow with a large spatial scale, such as flows around building, trees, and near-ground airflow boundary layer. Instead of solid fine particles, soap bubbles are used as the airflow tracer for reducing environmental impact. Typical bubble size provided by the present bubble generator is controlled around 20mm, at which the bubbles obviously have relative velocity to the airflow. We report three topics on the bubble tracking velocimetry(BTV) in this paper: 1) optics of bubble-imaging for quantitative visualization, and application to 3-D) visualization using color illumination, 2) theoretical estimation of bubble's relative velocity to airflow based on an equation of bubble's translational motion, 3) comparison of velocity vector field obtained by the BTV with that from cross-correlation PIV applied for smoke image. For the latter two topics, airflow around a NACA airfoil is chosen as the target of BTV measurement since it causes significant slip motion of soap bubbles from the airflow that accompanies shear rate, convective acceleration, pressure gradient, and separation.
  • Cheng Wen, Zhang-Bin Wang, Yuichi Murai, Fujio Yamamoto
    MULTIPHASE FLOW: THE ULTIMATE MEASUREMENT CHALLENGE, PROCEEDINGS 914 877 - + 2007年 [査読有り][通常論文]
     
    In bubbly two-phase flow, the gas phase and liquid phase have different flow fields. The mathematical expression for the motion of a small bubble at low Re number has been already established, the liquid velocity along the trajectory of the bubble is calculated inversely by using the motion equation. Whole field liquid flow structure has also estimated using a spatial and/or temporal interpolation method. This paper proposes an algorithm for estimating the liquid phase flow field based on measurement data on bubble data on bubble motion. The applicability of the algorithm is examined with Taylor-Green vortex flow as an analytical test case. Meanwhile, The result based on the theory, has been applied to reconstruct liquid phase velocity field by using the data of bubble velocity in an aeration tank.
  • 水平壁面乱流境界層内の単一気泡がもたらす流動場変調
    大石義彦, 福田浩士, 村井祐一
    日本機械学会論文集 B編 73 730 1298 - 1306 2007年 [査読有り][通常論文]
  • 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年 [査読有り][通常論文]
  • Particle Image Velocimetry for Air Flows Behind Permeable Cylinders
    H.TAKEUCHI, Y.OISHI, Y.TASAKA, Y.MURAI, Y.TAKEDA
    The 2nd Hokkaido University - Seoul National University Symposium on Mechanical and Aerospace Engineering 88  2007年01月 [査読無し][通常論文]
  • PTV Assessment of Friction-Modifying Events in Bubbly Turbulent Shear Flow
    Y.OISHI, H.FUKUDA, Y.MURAI, F.YSMSMOTO, Y.TAKEDA
    Proc. The5th Int. Symposium on Measurement Techniques for Multiphase Flows 567 - 571 2006年12月 [査読有り][通常論文]
  • 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年11月 [査読有り][通常論文]
  • Takehiro Ido, Yuichi Murai
    FLOW MEASUREMENT AND INSTRUMENTATION 17 5 267 - 275 2006年10月 [査読有り][通常論文]
     
    A new type of interpolation algorithm for particle tracking velocimetry is proposed. The algorithm is established based on a combination of ellipsoidal differential equations, i.e. a recursive process from a lower to a higher order interpolation. Each equation is solved as a boundary value problem by using the discrete velocity vector information as boundary conditions. In this paper the performance of the interpolation scheme, such as errors and cross correlations, is examined using the Taylor-Green vortex flow and isotropic turbulent flow. The examination results reveal that the recursive process from linear to hexagonal interpolation provides the best reconstruction in comparison to the single process. A quantitative evaluation is also carried out for integral and derivative information of the velocity vector, such as stream function and vorticity. (c) 2006 Elsevier Ltd. All rights reserved.
  • Y. Murai, Y. Oishi, Y. Takeda, F. Yamamoto
    EXPERIMENTS IN FLUIDS 41 2 343 - 352 2006年08月 [査読有り][通常論文]
     
    Particle tracking velocimetry (PTV) is applied to a bubbly two-phase turbulent flow in a horizontal channel at Re = 2 x 10(4) to investigate the turbulent shear stress profile which had been altered by the presence of bubbles. Streamwise and vertical velocity components of liquid phase are obtained using a shallow focus imaging method under backlight photography. The size of bubbles injected through a porous plate in the channel ranged from 0.3 to 1.5 mm diameter, and the bubbles show a significant backward slip velocity relative to liquid flow. After bubbles and tracer particles are identified by binarizing the image, velocity of each phase and void fraction are profiled in a downstream region. The turbulent shear stress, which consists of three components in the bubbly two-phase flow, is computed by analysis of PTV data. The result shows that the fluctuation correlation between local void fraction and vertical liquid velocity provides a negative shear stress component which promotes frictional drag reduction in the bubbly two-phase layer. The paper also deals with the source of the negative shear stress considering bubble's relative motion to liquid.
  • 伊東 哲也, 村井 祐一, 上埜 安隆, 大岩 浩司, 宮城 直樹, 山本 富士夫
    可視化情報学会論文集 26 4 27 - 32 The Visualization Society of Japan 2006年06月 [査読有り][通常論文]
     
    トロコイドギヤポンプは，トロコイド曲線を持つ内外２つのギヤで流体を封入する複数の密閉室が回転することで，流体を輸送するポンプである．このポンプでは密閉室の位置と形状が回転に伴って時間的に変化し複雑な流動を持つ．特にギヤのクリヤランス部を通る流れがポンプの性能を支配するため，トロコイドギヤポンプの可視化装置を設計・製作し，密閉室内の流動をRe＝300～10000の範囲で可視化した．可視化のトレーサ粒子としては，微小平板形状のカリロスコープ粒子(公称サイズ：30μｍｘ6μｍｘ0.07μｍ)を用いた．可視化された時系列画像を位相統計することで，密閉室内の流動構造のレイノルズ数依存性，容積効率依存性が明らかとなった．具体的には、Re＝1600～2000において流れが乱流遷移すること，この乱流化の主要因がギヤのクリアランス部から上流側に向けて逆流する噴流であることなどが見いだされた．
  • 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年04月 [査読有り][通常論文]
  • MURAI Yuichi, FUJII Hideki, TASAKA Yuji, TAKEDA Yasushi
    Journal of Fluid Science and Technology 1 1 12 - 23 The Japan Society of Mechanical Engineers 2006年 [査読有り][通常論文]
     
    Ultrasound velocity profiler (UVP) is applied to measurements of a horizontal turbulent bubbly channel flow to ascertain the mechanism of bubble-induced frictional drag reduction. Typical parameter regimes of the target flow are Re number of 0.6-6.0 x104, void fraction of 0-3%, and bubble diameter of 10-50mm. Since the UVP system only outputs velocity profiles on an ultrasound beam inside a liquid phase, a signal processing method for raw velocity data is proposed and used to detect the bubble interface. A conditional averaged liquid phase velocity profile that excludes gas phase data, has shown for the first time the structure of a turbulent boundary layer altered by large buoyant bubbles sliding along the channel wall.
  • Y Murai, S Yoshikawa, S Toda, M Ishikawa, F Yamamoto
    NUCLEAR ENGINEERING AND DESIGN 236 1 94 - 106 2006年01月 [査読有り][通常論文]
     
    Air-water two-phase flow in helically coiled tubes is investigated experimentally to elucidate the effects of centrifugal acceleration on the flow regime map and the spatial and the temporal flow structure distribution. Three kinds of test tubes with 20 mm inner diameters including a straight tube are used to compare the turbulent flow structure. Superficial velocities up to 6 m/s are tested so that the centrifugal Froude number covers a range from 0 to 3. The interfacial structure is photographed from two directions by a high-speed video system with synchronized measurement of local pressure fluctuations. The results reveal that the flow transition line alters due to centrifugal force acting on the liquid phase in the tube. In particular, the bubbly flow regime is narrowed significantly. The pressure fluctuation amplitude gets large relatively to the average pressure loss as void fraction increases. The frequency spectra of the pressure fluctuation have plural peaks in the case of strong curvature, implying that the periodicity of slugging two-phase flow is collapsed by an internal secondary flow activated inside the liquid phase. Moreover, under large Froude number conditions, the substantial velocity of the gas phase that biases to the inner side of the helical coil is slower than the total superficial velocity because the liquid flow is allowed to pass through the outer side and so resembles a radial stratified flow. (c) 2005 Elsevier B.V. All rights reserved.
  • Yuichi Murai, Jian Wu Qu, Fujio Yamamoto
    Multiphase Science and Technology 18 2 175 - 197 2006年 [査読有り][通常論文]
     
    Three-dimensional bubble-bubble interaction in quiescent liquid is investigated experimentally using a stereoscopic bubble-tracking technique. An accurate labeling method and a three-dimensional stereo-matching method are applied to the measurement of the three-dimensional centroid for individual bubbles. The velocity vectors of the bubbles are measured by a 3-D four-time-step tracking algorithm and then the relative velocity vectors of two nearest-neighbor bubbles are captured with high statistic reliability. With the measurement data for intermediate Reynolds numbers ranging from 5 to 75, the vertical attraction and the horizontal repulsion are confirmed for Re < 10 as known by a past study based on Navier-Stokes simulation. The new finding of the present measurement is that bubbles of Re > 30 have more repulsive velocity both in the horizontal and the vertical directions because they rise closely. Moreover, the three-dimensional structure of the bubble-bubble interaction is discussed with the data analysis of the interaction vector fields.
  • 近藤 貴幸, 田坂 裕司, 村井 祐一, 武田 靖
    年次大会講演論文集 2006 197 - 198 一般社団法人日本機械学会 2006年 
    Thermal efficiency of polymer electrolyte fuel cell extremely depends on a water distribution in Gas Diffusion Layer (GDL). Fuel cell model was prepared in order to investigate the water distribution in GDL by ultrasonic techniques. Acoustic impedance of GLD, which is porous plate of carbon, was estimated as bulk model to know approximated value of reflection ratio of ultrasonic echo. We attempted to measure an instantaneous ultrasonic echo that changes by the quantity of the water to detect existing water in GDL.
  • W Cheng, Y Murai, F Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 16 5 303 - 308 2005年10月 [査読有り][通常論文]
     
    In bubbly two-phase flow, the gas phase and liquid phase have different flow fields. The relative velocity of the two phases depends on the motion characteristic of the bubbles. The mathematical expression for the motion of a small bubble at low Reynolds number is already established. Using the equation, the liquid velocity along the trajectory of the bubble is calculated inversely using the motion equation. Whole field liquid flow structure is also estimated using a spatial and/or temporal interpolation method. This paper proposes an algorithm for estimating the liquid phase flow field from measurement data on bubble motion. In order to verify this principle, Taylor-Green vortex flow and Karman vortex shedding from a square cylinder have been chosen. The results reveal that by combining the inverse analysis and PTV with the spatio-temporal post-processing algorithm one can reconstruct well the carrier phase flow of the gas-liquid two-phase flow. (c) 2005 Published by Elsevier Ltd
  • PIV Measurement of Gas-Liquid Two-Phase Flows
    F.YAMAMOTO, Y.MURAI, T.SASAKI, Y.OISHI, H.FUKUDA
    Proc. 8th FLUCOME 2005 103 - 104 2005年08月 [査読無し][通常論文]
  • Two-Phase PTV for Bubbly Turbulent Boundary Layer and New Findings on Microbubble Drag Reduction Mechanism
    Y.MURAI, Y.OISHI, F.YAMAMOTO
    Proc. 6th Int. Symp. on Particle Image Velocimetry, Pasadena 1 - 7 2005年08月 [査読有り][通常論文]
  • Y Murai, H Oiwa, T Sasaki, K Kondou, S Yoshikawa, F Yamamoto
    MEASUREMENT SCIENCE AND TECHNOLOGY 16 7 1459 - 1468 2005年07月 [査読有り][通常論文]
     
    Air-water two-phase flow in a helically coiled tube is investigated, using backlight imaging tomography to elucidate the effect of centrifugal acceleration on phase distribution and interfacial structure. Superficial velocities up to 6 in s(-1) in 20 min diameter tube are tested. We focused on a slug flow regime in which centrifugal acceleration dominates the flow. The interfacial structure is visualized in six directions using a set of originally designed mirror-mounted water jackets. A temporal expansion image is made from line-sampled images and is used to reconstruct phase distribution through a linear backward projection algorithm. The present topography measurement showed various new features of gas-liquid two-phase flow in a helically coiled tube, such as a wall-covering effect in the case of high superficial velocity.
  • Turbulent Shear Stress Profiles inaHorizontal Bubbly Channel Flow using PTV
    Y.OISHI, Y.MURAI, Y.KODAMA, F.YAMAMOTO
    2nd International Symposium on Seawater Drag Reduction 2005年05月 [査読有り][通常論文]
  • Modification of Skin Frictional Drag of Gas-Liquid Two-Phase Flow in a Horizontal Channel
    H.FUKUDA, Y.OISHI, Y. MURAI, Y.KODAMA, F.YAMAMOTO
    2nd International Symposium on Seawater Drag Reduction 2005年05月 [査読有り][通常論文]
  • W Cheng, Y Murai, T Sasaki, F Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 16 1 35 - 46 2005年03月 [査読有り][通常論文]
     
    An image analysis method for measuring bubble velocity fields at high bubble number density is proposed. It is based on computing the cross correlation of bubble images with multiple spatial resolutions, i.e. a recursive cross correlation technique. Comparing several PTV and PIV schemes, it is confirmed that the recursive cross correlation leads to the best measurement results because of the robustness with respect to optical and dynamic characteristics of bubbles. The method is applied successfully to the measurement of bubble motion in bubble plumes accompanying a strong unsteadiness over a wide frequency range. The results reveal that the high frequency fluctuations of bubble velocities grow in the shear layer and near the top surface, while low frequency fluctuations dominate in the middle part of the tank. The characteristic frequency divides the frequency spectrum of the bubble fluctuation intensity into two regions: where there are turbulent behaviors and where there are macroscopic convection patterns in the bubble plumes. (C) 2004 Elsevier Ltd. All rights reserved.
  • Ct-Based visualization of Gas-Liquid Two-Phase flow in helically coiled tubes
    Hiroshi Oiwa, Yuichi Murai, Toshio Sasaki, Shinji Yoshikawa, Fujio Yamamoto
    4th World Congress in Industrial Process Tomography 428 - 433 2005年 
    Air-water two-phase flow in a helically coiled tube is investigated using backlight imaging tomography to elucidate the effect of centrifugal acceleration on phase distribution and interfacial structure. Superficial velocities up to 6 m/s in 20mm-diameter tube are tested. We focused on a slug flow regime in which centrifugal acceleration dominates the flow. The interfacial structure is visualized in six directions using a set of originally designed mirror-mounted water jackets. A temporal expansion image is made from line-sampled images, and is used to reconstruct phase distribution through a linear backward projection algorithm. 3D PTV is also carried out to capture a secondary flow induced by the curvature. The present topography measurement showed a V-shaped interface and a wallcovering effect of liquid in the case of high superficial velocity.
  • 芦原将彰, 北川石英, 村井祐一, 山本富士夫
    日本機械学会論文集B編 71 710 2393 - 2400 2005年 [査読有り][通常論文]
     
    Wall-sliding bubbly flow is experimentally investigated using a shallow focus imaging technique. The technique allows to capture the motion of tracer particles inside a thin layer from a wall. Adding digital image processing provides further fine spatial resolution up to 100 ratio of the length of the viewing area to the focused thickness. Bubble-bubble interaction, which is one of dominant phenomena in wall-sliding bubbles, is analyzed with using Particle Tracking Velocimetry applied to both phases. Transition of bubbles' pattern from vertically chained to horizontally clustered arrangement is discussed with the local liquid phase flow structure around individual bubble. The results reveal that the temporally high fluctuation velocity in the liquid phase generates during the transition, and the circulation of bubble-vicinity liquid induces rapid transition of the arrangement.
  • 大岩 浩司, 村井 祐一, 山本 富士夫
    日本機械学会論文集Ｂ編 71 706 1550 - 1557 2005年 [査読有り][通常論文]
     
    The fractional drag reduction provided with small bubbles is investigated experimentally using vertical concentric cylinders. The friction reduction ratio is measured using a torque meter mounted on the inner cylinder for a wide range in Reynolds number from wavy vortex flow (WVF) to turbulent Taylor vortex flow (TTV). The present data show around 36% drag reduction in the case of WVF regime at Re = 600 and the reduction maintains until Re=4 000. The friction reduction ratio η defined by the unit void fraction obeyed in a linear relation with inverse values of Froude number, and reached up to 10 in the best case, that implies the highest sensitivity for the drag reduction. The bubble distribution measured in the gap showed a peak near the inner cylinder surface resulting in high local shear stress reduction.
  • 大石 義彦, 村井 祐一, 福田 浩士, 児玉 良明, 山本 富士夫
    日本機械学会論文集Ｂ編 71 706 1542 - 1549 2005年 [査読有り][通常論文]
     
    Skin frictional drag of bubbly two-phase mixture in a horizontal turbulent channel is investigated experimentally using a shear stress sensor and a high-speed video camera. We choose non-micro bubbles having a size of 1 to 10 mm intentionally to confirm that the drag reduction still works with relatively large bubbles to the channel height. The measurement results have shown that the drag reduction realized in case of a void fraction higher than a critical value that depends on liquid flow velocity. Also, significant bubble size dependence was found in the region near bubble injector. A synchronized measurement of local shear stress and interfacial structure has newly shown that the instantaneous friction factor decreased in rear part of individual bubble.
  • Qu Jian-wu, Yuichi Murai, Fujio Yamamoto
    JOURNAL OF HYDRODYNAMICS 17 2 243 - 251 2005年 [査読有り][通常論文]
     
    Bubble-bubble interaction in free rising bubbly flows is experimentally investigated in the present study. The velocity vectors of the bubbles are measured by a stereoscopic bubble-tracking technique and then the relative velocity vectors of two nearest-neighbor bubbles are calculated with high statistical reliability. With the measurement data at Reynolds number ranging from 5 to 75, the vertical attraction and the horizontal repulsion are confirmed for Re < 10 as known by the past study based on Navier-Stokes simulation. The new finding of the present measurement is that the bubbles of Re > 30 have repulsive velocity bothin the horizontal and the vertical directions as those rise closely. Moreover, the three-dimensional structure of the bubble-bubble interaction is discussed with the data analysis of the interaction vector fields.
  • Y Murai, T Sasaki, MA Ishikawa, F Yamamoto
    JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME 127 1 117 - 123 2005年01月 [査読有り][通常論文]
     
    This paper is concerned with flow visualization and image measurement of bubbly flows around various shapes of cylinders. A coaxial confined double rectangular chamber is constructed in order to provide a wide two-dimensional uniform bubble distribution upstream. The experiment shows that a wide two-phase convection is induced around the obstacle, though such an effect is not observed in research on the single-phase flow around objects. The spatial scale of the two-phase convection depends sensitively on the shape of the obstacle. Dense arrangement of cylinders is also investigated to find the interaction among the convection. The measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by image processing including particle tracking velocimetry, explore the detailed mechanism of generating the convection.
  • 山本 富士夫, 村井 祐一
    可視化情報学会誌 25 2 255 - 256 The Visualization Society of Japan 2005年 
    The analytical algorithm of PIV and PTV has advanced in the last two decades from simple cross correlation method to binary image cross correlation method, Delaunay tessellation method, velocity, gradient tensor method, and recursive cross correlation method. In parallel, useful post-processing schemes for PIV/PTV such as ellipsoidal equation method and inverse analysis method were proposed so that detailed flow structure could be evaluated including pressure field. This paper concerns with such a history of the research and future possibility for further advance of the PIV/PTV.
  • 伊東 哲也, 村井 祐一, 上埜 安隆, 大岩 浩司, 宮城 直樹, 山本 富士夫
    可視化情報学会誌 25 2 303 - 304 The Visualization Society of Japan 2005年 
    Flow visualization of an inscribed gear pump is carried out to grasp the influence of deformation rate and the rotation of the fluid chamber provided by the two trochoid gears. A transparent model of the pump, which resists friction, is made. A platelet type of light-reflecting tracer particles "Kalliroscope" is adopted and applied to the visualization of flow patterns. Upon taking phase-statistic for the time serial images, the dependence of the flow on Reynolds number is evaluated.
  • 大橋 順一, 稲葉 一昌, 田坂 裕司, 村井 祐一, 武田 靖
    可視化情報学会誌 25 2 289 - 290 The Visualization Society of Japan 2005年 
    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.
  • 大石 義彦, 福田 浩士, 村井 祐一, 山本 富士夫
    可視化情報学会誌 25 1 29 - 30 The Visualization Society of Japan 2005年 
    Skin frictional drag of the gas-liquid two-phase flow is investigated using silicon oil in a horizontal channel. The silicon oil has three characteristics, i.e. stable interfacial property, high viscosity, and low surface tension in comparison to water. The present study is planned to grasp the skin friction characteristics modified with bubbles in the oil. The measurement and the visulization results show increment of the frictional drag by bubbles because of promotion of the laminar to turbulent flow transition. Bubble shapes changing with the transition is also discussed.
  • Y. Murai, H. Oiwa, Y. Takeda
    14TH INTERNATIONAL COUETTE TAYLOR WORKSHOP 14 143 - 156 2005年 [査読有り][通常論文]
     
    Bubble distributions organized in a vertical Taylor-Couette flow are experimentally investigated. Modification of shear stress due to bubbles is measured with a torque sensor installed on the rotating inner cylinder. The wall shear stress decreases as bubbles are injected in all the tested range of Re from 600 to 4500. The drag reduction ratio per void fraction measured in the present experiment, which indicates net gain of the drag reduction, has been evaluated. The gain was more than unity for Re<2000 while it descends negative for Re>4000. The maximum gain achieved was around 10 at Re=600, at which point the bubbles dispersed widely on the inner cylinder surface and effectively restrict momentum exchange of fluid between the two walls. The expansion of Taylor vortices in the vertical direction by the presence of bubbles was confirmed by flow visualization including particle tracking velocimetry. Such bubble behaviours interacting with Taylor vortices are discussed in detail in this paper.
  • J Huang, M Ashihara, Y Murai, Y Kodama, SM Wang, F Yamamoto
    ISTM/2005: 6TH INTERNATIONAL SYMPOSIUM ON TEST AND MEASUREMENT, VOLS 1-9, CONFERENCE PROCEEDINGS 5220 - 5223 2005年 [査読有り][通常論文]
     
    Experiments were performed to measure the flow structures of turbulent bubbly flow in a horizontal channel with PTV Streamwise and spanwise components of velocities in the boundary layer were obtained using shallow focal imaging technique which enabled to visualize the motion of bubbles and tracer particles suspended in the near-wall region. Measurements results at three locations downstream a bubble injector showed that the average streamwise velocity in the vicinity of the wall was attenuated by presence of bubbles, implying the reduction of skin frictional resistance.
  • IOP Journal of Physics: Conference Series: Vol.14, 14th International Couette-Taylor Workshop -Sapporo 2005 (2005)
    Institute of Physics UK 2005年 [査読無し][通常論文]
  • Direct measurement of wall-shear stress and flow visualization of bubbles in a horizontal channel
    H.FUKUDA, Y.MURAI, Y.OISHI, M.KOUKAWA, F.YAMAMOTO
    Proc. of International Symposium on Advanced Mechanical Engineering, Between University of Fukui – Pukyong National University 253 - 258 2004年11月 [査読有り][通常論文]
  • Shallow Focal Particle Image Velocimetry for Bubbly Flows In a Wall Boundary Layer
    Y.OISHI, M.ISHIKAWA, Y.MURAI, F.YAMAMOTO
    Proc. of 7th Asian Symposium on Visualization CD-ROM, 2B-4,  2004年11月 [査読有り][通常論文]
  • A Kitagawa, K Sugiyama, Y Murai
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 30 10 1213 - 1234 2004年10月 [査読有り][通常論文]
     
    Bubble-bubble interactions in a wall-sliding bubble swarm are investigated experimentally using a particle tracking velocimetry (PTV) technique. Firstly, the drag coefficient of a single wall-sliding bubble is measured, in which the distance between the wall and the bubble interface is much shorter than the average bubble diameter. Secondly, the probability distribution of the nearest bubble around individual bubbles in the bubble swarm is detected in the range from Re = 1 to around 20. Two kinds of statistical sampling techniques are used in order to identify the two-dimensional structure of the bubble-bubble interactions. A local modification of the drag coefficient in the swarm is obtained by calculating the interactive velocity of an individual bubble. Furthermore, the transition of a bubble's arrangement in the swarm is discussed by computing the relative velocity vector. The feature of the interaction patterns obtained by these techniques is classified based on Reynolds number. (C) 2004 Elsevier Ltd. All rights reserved.
  • PIV Measurement of Turbulent Bubbly Two-Phase Flow in a Horizontal Channel
    J.HUANG, M.ASHIHARA, Y.OISHI, Y.MURAI, Y.KODAMA, F.YAMAMOTO
    Proc. of the 4th International Symposium on Measurement Techniques for Multiphase Flows 2004 253 - 259 2004年09月 [査読有り][通常論文]
  • Particle Tracking Velocimetry of Turbulent Bubbly Flows in a Horizontal Channel
    Y.MURAI, Y.OISHI, Y.KODAMA, F.YAMAMOTO
    Proc., of the 7th International Congress on Optical Particle Characterization 41 1 - 5 2004年08月 [査読有り][通常論文]
  • 大岩 浩司, 村井 祐一, 山本 富士夫
    日本機械学会論文集Ｂ編 70 697 2286 - 2293 2004年 [査読有り][通常論文]
     
    The effective viscosity of bubbly liquid is measured by means of falling sphere method in Stokes drag region. The method can evaluate the influence of bubble's transient deformation around the falling sphere. The relative viscosity, which is defined by the effective viscosity divided by the single-phase viscosity, is directly obtained by the ratio of the terminal falling velocity of the sphere. The results have shown the following points. 1) The relative viscosity at low capillary number agrees to the theoretical formula for the spherical bubble dispersion. 2) The relative viscosity drops down to less than unity as the capillary number gets higher than a critical value. 3) The critical capillary number is around 3.5 for the falling sphere method, and is much larger than that for simple shear flow. 4) The effective viscosity increasing mechanism by bubble's transient deformation is discussed with visualization results and some theoretical works done in the past.
  • 宮城 直樹, 村井 祐一, 宮崎 孝司, 山本 富士夫
    日本機械学会論文集 B 72 714 375 - 382 2004年 [査読有り][通常論文]
  • Qu Jian-wu, Yuichi Murai, Fujio Yamamoto
    JOURNAL OF HYDRODYNAMICS 16 6 756 - 766 2004年 [査読有り][通常論文]
     
    A Particle Image Velocimetry (PIV) method based on the image separation and reconstruction with the median filter and triangular Bezier patch was proposed to measure multiple velocity fields from single-camera images in the present study. The method was examined on synthetic PIV images with the Green-Taylor two-phase vortex flows and the test results showed high accuracy and highly correct tracking percent compared with the exact solution. An experiment of the bubbly jet flow was also conducted as a practical demonstration of the present method. As a result, it is confirmed from the simulation image examination and the experimental measurement that the proposed method shows a good performance in the measurement of bubble and particle phases.
  • 大石 義彦, 村井 祐一, 山本 富士夫
    可視化情報学会誌 24 1 125 - 126 The Visualization Society of Japan 2004年 
    Particle tracking velocimetry is applied to a bubbly two-phase flow in a horizontal channel to investigate the mechanism of turbulent shear stress reduction using bubbles. We derived three componential stresses to express the phenomenon hidden in the turbulent shear layer and measured them with the PTV data at Re=4×104. It is newly found that the role of a vertically correlated shear stress is important to reduce the total stress effectively.
  • 福田 浩士, 大石 義彦, 村井 祐一, 山本 富士夫
    可視化情報学会誌 24 1 111 - 112 The Visualization Society of Japan 2004年 
    As a basic study of skin friction reduction using bubbles, the relationship between the skin friction and the bulk void fraction in a horizontal rectangular channel is investigated experimentally for Re=9700. The skin friction is reduced for the void fraction larger than 17% in our test facility, in which the bubble size ranges from 2 to 30mm. The negative correlation between the local skin friction and the local void fraction is confirmed by a time-resolved synchronized measurement, and we also found that the local skin friction decreased in the rear region of large bubbles.
  • 村井 祐一, 瞿 建武, 山本 富士夫
    可視化情報学会誌 24 1 173 - 174 The Visualization Society of Japan 2004年 
    This paper concerns with experimental measurement of bubble-bubble interaction in a free-rising bubbly flow using three-dimensional Particle Tracking Velocimetry (3-D PTV). An accurate labeling method is employed to measure correctly the center of gravity for individual bubble so that the relative velocity vector in a swarm of bubbles is captured with high statistic reliability. The bubble-bubble interaction is discussed for the range of 5
  • 村井 祐一, 戸田 信一, 山本 富士夫
    年次大会講演論文集 2004 259 - 260 一般社団法人日本機械学会 2004年 
    Helical coil type heat exchanger tubes are used in the evaporator and the superheater of the prototype fast-breeder reactor (FBR) Monju. The present study visualizes the flow pattern of gas-liquid two-phase flow in the helical tubes to clarify the influence of centrifugal acceleration due to the curvature. The three-dimensional interfacial structure is measured using CT from the backlight projection image acquired in six directions at a local section. The results have shown that the interfacial structure became asymmetric in the case of high Ga number, oiwing to combination of gravity and centrifugal acceleration.
  • 大石 義彦, 福田 浩士, 村井 祐一, 児玉 良明, 山本 富士夫
    年次大会講演論文集 2004 243 - 244 一般社団法人日本機械学会 2004年 
    Experiments were carried out to measure skin friction in a horizontal rectagular channel flow which contains various size of air bubbles. First of all, the relationship between the bubble motion and the temporal fluctuation of local skin friction is investigated experimentally at Re =l.lx10^4, in which approximate bubble size ranges from 3 to 30mm. The negative correlation between the local skin friction and the local void fraction is confirmed by simultaneous measurement of shear stress and interfacial visualization. It became clear that the local skin friction decreased in the rear region of large bubbles. Secondly, particle tracking velocimetry is applied to a bubbly two-phase flow to investigate the mechanism of turbulent shear stress modification. We measured three componential stresses with the PTV data at Re=2.0x10^4 and found that a role of the vertically correlated shear stress was important to reduce the total stress effectively.
  • 笹木 俊男, 黒田 一郎, 永井 二郎, 村井 祐一, 山本 富士夫
    年次大会講演論文集 2004 253 - 254 一般社団法人日本機械学会 2004年 
    Alkaline water electrolysis is the one of technologies of hydrogen production through decomposition of water by an electric power. The present study aims at improvement of hydrogen production in 'water electrolysis from viewpoint of generated bubbles' behavior, which interrupts the electric current between two electrodes. The measurement of electric current and the visualization of bubbly flow are practiced simultaneously to discuss the influence of the two-phase flow structure onto the water electrolysis. The paper describes two experiments on the micro-channel water electrolysis and on the water electrolysis by use of vibrating electrodes.
  • Yuichi Murai, Naoki Miyagi, Koji Miyazaki, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 70 695 1754 - 1761 2004年 [査読有り][通常論文]
     
    The pumping characteristics and the internal flow structure of an inscribed trochoid gear pump are investigated by means of three-dimensional numerical simulation. Cartesian grid system is employed to calculate the fluid flow while the boundary conditions on rigidly rotating gear surface is expressed with Lagrangian markers. The results reveal that the flow rate and the pressure rise obtained by the pump become the highest at Re=10 when the clearance between the two gears is considered. At lower Re numbers, the shear stress transfer on the gear surface fluctuates significantly resulting into lower performance. For higher Re numbers, backward induced jet flow through the clearance makes the internal flow complicated due to non-uniform centrifugal acceleration.
  • Toshio Sasaki, Masaaki Ishikawa, Yuichi Murai, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 70 689 60 - 68 2004年 [査読有り][通常論文]
     
    Bubble-driven flow around circular cylinders in a narrow channel is experimentally investigated by means of image processing. The cylinders are settled in the channel with three kinds of arrangement pattern to clarify the difference of the internal two-phase flow structure. Thinning algorithm is applied to the detection of all the bubbles in order to measure the bubble motion in locally high void fraction. Size and spatial distribution of the bubbles are also obtained with the image analysis to discuss the bubble's coalescence/fragmentation due to the collision with the cylinders. The results imply that the rising velocity of the bubble is governed not only by bouncing on the cylinders but also by the liquid phase flow pattern that is sensitively dependent on the gas flow rate and the cylinders' arrangement pattern.
  • F Yamamoto, M Koukawa, Y Murai, JW Qu
    MULTIPHASE, NON-NEWTONIAN AND REACTING FLOWS, VOL 2, PROCEEDINGS 23 - 27 2004年 [査読有り][通常論文]
     
    Several novel techniques of PIV including PTV and new results on gas-liquid two-phase flows are introduced in this invited lecture. Instead of Laser-based illumination in PIV, shallow focal imaging technique is available to capture the images of gas-liquid two-phase flows with high image quality and low cost. Multi-velocity field PIV extends conventional PIV to measure simultaneously the flow fields of the liquid phase and gas phase from single-camera images with a high accuracy. The inverse analysis technique makes it possible to estimate carrier liquid phase flow velocities from measurement data of dispersed bubble motion when the dispersion motion is measured with PIV. These techniques have wide practical application in industrial processes, such as micro-bubble drag reduction for ship, etc.
  • F Yamamoto, Y Murai
    RECENT ADVANCES IN FLUID MECHANICS 45 - 50 2004年 [査読有り][通常論文]
     
    Several novel techniques of PIV including PTV and new results on gas-liquid two-phase flows are introduced in this invited lecture. Instead of Laser-based illumination in PIV, shallow focal imaging technique is available to capture the images of gas-liquid two-phase flows with high image quality and low cost. Multi-velocity field PIV extends conventional PIV to measure simultaneously the flow fields of the liquid phase and gas phase from single-camera images with a high accuracy. The inverse analysis technique makes it possible to estimate carrier liquid phase flow velocities from measurement data of dispersed bubble motion when the dispersion motion is measured with PIV These techniques have wide practical application in industrial processes, such as micro-bubble drag reduction for ship, etc.
  • Cheng Wen, Yuichi Murai, Toshio Sasaki, Fujio Yamamoto
    JOURNAL OF HYDRODYNAMICS 16 6 730 - 736 2004年 [査読有り][通常論文]
     
    An inverse analysis algorithm is proposed for estimating liquid phase flow field from measurement data of bubble motion. This kind of technology will be applied in future for various estimation of fluid flow in rivers, lakes, sea surface flow, and also microscopic channel flow as the problem-handling in civil, mechanical, electronic, and chemical engineering. The relationship between the dispersion motion and the carrier phase flow is governed and expressed by the translational motion equation of spherical dispersion. The equation consists of all the force components including inertia, added inertia, drag, lift, pressure gradient force and gravity force. Using this equation enables us to estimate the carrier phase flow structure using only the data of the dispersion motion. Whole field liquid flow structure is also estimated using spatial or temporal interpolation method. In order to verify this principle, the Taylor-Green vortex flow, and the Karman vortex shedding from a square cylinder have been chosen. The results show that the combination of the inverse analysis and Particle Tracking Velocimetry (PTV) with the spatio-temporal post-processing algorithm could reconstruct well the carrier phase flow of the gas-liquid two-phase flow.
  • Shallow Focal Particle Image Velocimetry for Bubbly Flow in the Vicinity of the Wall
    F.YAMAMOTO, Y.MURAI, M. ISHIKAWA, Y.OISHI
    Proc., of the International Symposium 2003 on Advanced Mechanical Engineering 35 - 40 2003年11月 [査読無し][通常論文]
  • Experimental and numerical simulation of three-phase flow in an aeration tank
    Wen Cheng, Xiao-De Zhou, Ce Song, Tao Min, Yuichi Murai, Fujio Yamamoto
    Journal of Hydrodynamics 15 4 118 - 123 2003年08月 
    Aeration plays an important role in the treatment of activated sludge due to the interactions among bubbles, sewage and activated sludge in an aeration tank. The aeration performance is directly concerned with the efficiency of sewage disposal. So the three-dimensional two-fluid model was established with emphasis on the phase interaction terms in this paper. This model, as an extension of the two-phase flow model, involved the motion laws of three-phases, and was compared with experimental studies. The finite volume method was used in the numerical simulation of gas-liquid two-phase flow and gas-liquid-solid three-phase flow. In order to discuss the influence of gas-phase, liquid-phase and solid-phase motions in an aeration tank on the sewage disposal, three kinds of boundary and initial conditions were adopted. The simulated results of the flow structure show qualitatively good agreement with the experimental data. And the theoretical basis for designing the best aeration tank was discussed according to the simulated results.
  • Qu Jianwu, Murai Yuichi, Yamamoto Fujio
    可視化情報学会誌. Suppl. 23 1 247 - 250 The Visualization Society of Japan 2003年07月01日 
    Bubble-Bubble interaction in a free-rising bubbly flow is measured with three-dimensional Particle Tracking Velocimetry (3-D PTV). The present report mentions the dependency of the interaction pattern on Reynolds number of rising bubble from 5 to 75. With the measurement data, it has been newly found that high Re number bubbles had repulsive motion each other both in horizontal and vertical direction as the distance of bubbles was shortened. The technique of PTV for extracting accurately the 3-D velocity vectors of bubbles is also discussed.
  • Hiroshi Oiwa, Masa-Aki Ishikawa, Yuichi Murai, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 639 - 645 2003年 
    Effective viscosity of bubbly two-phase flow is experimentally investigated by means of the falling sphere method. The terminal falling velocity of the sphere is measured by image processing to calculate the relative viscosity of the two-phase flow to the single-phase flow. The measurement results show that the effective viscosity is reduced for a range from 0 to 2% of void fraction as the shearing Weber number increases. This fact implies that the reduction of the effective viscosity is governed by the deformation of the bubbles, and the mechanism is explained by the interruption of the shear stress transfer in the two-phase medium.
  • Masa-Aki Ishikawa, Hiroshi Oiwa, Kosuke Sakai, Yuichi Murai, Shin-Ichi Toda, Kiyoshi Tamayama, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 1453 - 1458 2003年 
    In the steam generator of the prototype FBR (Fast Breeder Reactor) in Japan, heat exchange tubes of helical coil type are utilized. The gas-liquid two-phase flows in the helical coil tube have different characteristic from straight tubes due to the effects of centrifugal acceleration in the curved tubes. In our study, the interfacial structure of the gas-liquid two-phase flows in the helical coil tube is visualized to provide the flow pattern map. Simultaneously, the pressure loss and its local fluctuation are measured in order to investigate the dynamic characteristics of the two-phase flow appearing in the helical coil tube. The result reveals that the bubbly flow regime extends and the stratified flow vanishes compared the gas-liquid flow in a horizontal straight tube. Moreover, the slug flow has asymmetric structure due to the effect of centrifugal acceleration. On the contrary the pressure loss is basically not remarkably different from the straight tube except the fact that the pressure has a high fluctuation component.
  • Bubble-Generated Convection in Immiscible Two-Phase Stratified Liquids
    Yuichi Murai, Hassan Abdulmouti, Yasushi Ohno, Masa-Aki Ishikawa, Dae Seok Bae, Fujio Yamamoto
    Proceedings of the ASME Fluids Engineering Division Summer Meeting 1 481 - 486 2003年 
    The technique of using a surface flow induced by a bubble plume is proposed to collect the surface-floating oil layer in case of oil-leakage accidents. The fundamental characteristics of the surface flow generation mechanism were presented in the last ASME FED summer meeting -2000. After that, we focus on the actual oil-transportation effect considering the stratified layer of oil on the free surface. In this case, the difference between two fluids in density and viscosity causes a quite unsteady interface motion. The laboratory model experiments and numerical simulation based on Eulerian-Lagrangian model have been carried out in order to investigate the multi-dimensional transportation of the oil due to bubbles. As a referential experiment, the liquid flow pattern of bubble-induced convection in a thermal stratified liquid has been also measured by using PIV in which a color-image processing is combined to measure the temperature field.
  • Takehiro Ido, Hiromasa Shimizu, Yoichi Nakajima, Masa-Aki Ishikawa, Yuichi Murai, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 2257 - 2263 2003年 
    Three-dimensional Particle Tracking Velocimetry (3-D PTV) is one of a useful measurement tools to understand complicated structure of flow. This paper concerns with a system of 3-D PTV based on color image processing using a liquid crystal image projector. The merit of the present system is inexpensive setup and needless of complicated procedure for stereo-pair matching of particles since all the process are carried out by single-camera. The accuracy of color-based PTV depends on the image quality and the optical characteristics of color-light scattering on tracer particles. After detailed discussion on these technical problems is mentioned, two kinds of experimental demonstration are shown by a chamber-inside steady flow and a vortex-shedding flow behind rectangular cylinder.
  • Masa-Aki Ashihara, Atsuhide Kitagawa, Masa-Aki Ishikawa, Akihiro Nakashinchi, Yuichi Murai, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 2277 - 2284 2003年 
    Bubble-bubble interaction is a quite fundamental issue to understand multiphase flow dynamics and to improve mathematical models of dispersed multiphase flow for higher volume fraction of dispersion. In this study, the bubble-bubble interaction is measured using Particle Tracking Velocimetry (PTV) in various environments. First, bubbles sliding on a vertical wall are measured using 2-D PTV. Second, the free rising bubbles in an unbounded space are measured applying 3-D PTV. Third, the simultaneous measurement for gas and liquid phases in the layer of wall-sliding bubbles is carried out. The measurement data have shown that the average bubble-bubble interaction patterns in the wall-sliding bubbles and in the free rising bubbles were attractive in the vertical direction and repulsive in the horizontal direction. The relation between the carrier phase flow structure and the bubbles' motion is detected to explain the mechanism of the bubble-bubble interaction.
  • Yuichi Murai, Masa-Aki Ishikawa, Toshio Sasaki, Fujio Yamamoto
    Proceedings of the ASME/JSME Joint Fluids Engineering Conference 2 1429 - 1435 2003年 
    This paper concerns with flow visualization and image measurement of bubbly flows around various shapes of cylinders. A coaxial confined double rectangular chamber is constructed in order to provide a wide two-dimensional uniform bubble distribution upstream of the obstacle. The experiment shows that a wide two-phase convection is induced around the obstacle, though such an effect is not observed in research on the single-phase flow around objects. The spatial scale of the two-phase convection depends sensitively on the shape of the obstacle. Dense arrangement of cylinders is also investigated to find the interaction among the convection. The measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by image processing including particle tracking velocimetry (PTV), explore the detailed mechanism of generating the convection.
  • 酒井 康丞, 村井 祐一, 戸田 信一, 吉川 信治, 石川 正明, 山本 富士夫
    年次大会講演論文集 2003 293 - 294 一般社団法人日本機械学会 2003年 
    Helical coil type heat exchanger tubes are used in the evaporator and the superheater of the prototype fast-breeder reactor (FBR) Monju. The present study visualizes the flow pattern of gas-liquid two-phase flow in the helical tubes to clarify the influence of centrifugal acceleration due to the curvature. Flow regime maps for two different curvature radii are obtained. The results reveal that the bubbly flow regime expands and stratified flow regime vanishes compared to the straight horizontal pipe flow owing to the centrifugal force acting on the liquid phase. The bubbly flow regime further expands if the curvature radius increases because of slowdown of the internal secondary flow induced by the centrifugal acceleration.
  • 大岩 浩司, 三ッ田 和彦, 石川 正明, 村井 祐一, 山本 富士夫
    年次大会講演論文集 2003 283 - 284 一般社団法人日本機械学会 2003年 
    Effective viscosity of liquid containing bubbles is experimentally investigated by means of the rotating coaxial cylinder method. The rotating coaxial cylinder method measures the relative viscosity of the two-phase fluid to the single-phase fluid from the torque for the inner cylinder by a torque meter. In this research, it is made clear that the viscosity characteristics of spherical bubble mixture. The measurement results show that the effective viscosity has a peak on the relationship with shear rate.
  • 村井 祐一, 石川 正明, 芦原 将彰, 衣川 甲輔, 山本 富士夫
    可視化情報学会論文集 23 1 1 - 8 社団法人 可視化情報学会 2003年 
    気泡流中では気泡どうしが接近すると，気泡間相互作用が発生する．これに関しては，従来まで数値解析によって整理が試みられているが，あらゆる距離と方向で包括的に実測した例はない．本研究では，3-D PTV(3次元粒子追跡型流速測定法)を気泡群の計測に応用し，Re=10の条件に対する3次元的な2気泡間の相互作用を検出した．気泡間相互作用は，気泡の平均上昇速度に対して微弱な変動成分であるとともに，気泡を全数計測しなければ正確な計測ができない．このため気泡像に対するテンプレートマッチング法によるラベリング，許容誤差をあたえたステレオマッチングを利用するなど，工夫を行った．結果より，鉛直方向に接近速度，水平方向に離間速度，斜め方向に捻り速度が生じることがわかった．このうち斜め方向に関する相互作用は，従来の数値解析では予測されておらず，本実験結果からの新しい知見である．
  • 程 文, 村井 祐一, 石川 正明, 山本 富士夫
    可視化情報学会論文集 23 11 107 - 114 The Visualization Society of Japan 2003年 
    気泡流中では気液二相が互いに異なる流場を持ち，その相対速度は，気泡の並進運動特性によって支配される．近年では低Re数気泡の運動方程式モデルはほぼ確立されており，原理的に，気泡の速度ベクトルデータから液相流場を逆算することが可能である．本研究では，気泡速度ベクトルから，気泡軌跡近傍の液相速度ベクトルを逆算する手法と，その時空間的補間スキームの組み合わせにより，液相の流場を詳しく推定するアルゴリズムを提案した．このようなアルゴリズムは，トレーサ粒子を大量に散布できない工業機器や自然環境計測において利用が期待される．本論文では，気泡の並進運動に関する周波数解析から気泡運動からの推定の合理性を示したうえで，Taylor-Greenの渦流れを用いて提案したアルゴリズムの解析的評価について論じた．また，実際の気泡画像に対する実験的デモンストレーションにより，その実用性を明らかにした
  • 北川 石英, 杉山 和靖, 笹木 俊男, 村井 祐一
    日本機械学会論文集B 69 681 1140 - 1147 2003年01月 [査読無し][通常論文]
     
    In this report, the effects of Reynolds number to the bubble-bubble interaction in a swarm of wall-sliding bubbles are investigated experimentally using PTV (Particle Tracking Velocimetry). Firstly, the drag coefficient of single wall-sliding bubble is measured for four kinds of liquid with different kinematic viscosity and is then compared to single bubble in an infinite liquid. Secondly, the difference of the bubble-bubble interaction among three types of Reynolds numbers, i.e. Re = 1.32, 2.83 and 15.42 is clarified using statistic data such as the interactive velocity vectors, the drag coefficient ratio and the presence frequency of the nearest bubbles. In particular, the discussion is focused on how the vorticity diffusion from the target bubble affects the nearest bubble.
  • T Ido, Y Murai, F Yamamoto
    EXPERIMENTS IN FLUIDS 32 3 326 - 336 2002年03月 [査読有り][通常論文]
     
    Accurate postprocessing methods are required in order to analyze the detailed flow structures from the scattered data of particle-tracking velocimetry (PTV). In particular, vorticity distributions and stream functions are not reasonably obtained by conventional methods. This paper proposes a new postprocessing algorithm based on ellipsoidal differential equations; this method utilizes data as discrete boundary conditions. The results obtained by the proposed algorithm fully satisfy the equation of continuity and simultaneously correspond well with the raw data. The performance of the algorithm is examined by applying it to two-dimensional vortex flows and isotropic turbulent flows. The results reveal that the present algorithm has the highest accuracy among several conventional methods for detecting vorticity and streamlines.
  • Y Murai, T Ido, F Yamamoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 45 1 142 - 149 2002年02月 [査読有り][通常論文]
     
    Our previous study confirmed that ellipsoidal differential equations can be used to interpolate particle tracking velocimetry (PTV) measurement results. In the preset study, we deal with extensions of the equations; to time serial processing and to the detection of mismatched vectors. The performance of these algorithms is evaluated by using the flow around a rectangular cylinder and a vortex flow. Furthermore, the actual advantages of utilization of these methods are discussed by applying them to the experimental result of sudden vortex generation due to the collision of a circular cylinder with a flat wall.
  • 村井 祐一, 石川 正明, 漁野 嘉昭, 戸田 信一, 遠藤 昭, 山本 富士夫
    年次大会講演論文集 2002 7 - 8 一般社団法人日本機械学会 2002年 
    Heat exchange tubes of helical coil type are utilized in the steam generator of the fast breeder prototype reactor "Monju". The gas-liquid two-phase flow in the tube is affected by the centrifugal acceleration owing to the constant curvature of the tube. This paper presents the flow pattern map obtained by visualization, and the interfacial structure analyzed by stereoscopic image processing for isothermal air-water system. The measurement results have shown that the flow pattern map was widely occupied by slug and plug flows, and the internal liquid slug had asymmetric behavior due to the curvature of the flow.
  • 笹木 俊男, 石川 正明, 村井 祐一, 山本 富士夫
    年次大会講演論文集 2002 323 - 324 一般社団法人日本機械学会 2002年 
    Numerical and experimental investigations on bubbly channel flows through closely arranged cylinders have been carried out. This paper concerns with the results of the three-phase simulation using Eulerian-Lagragian model in which the cylinder-bubble interaction model is taken into account. The results show that rising velocity of bubbles decreases due to the bouncing of the bubbles at the cylinder surface, and the characteristic scale of the liquid flow is altered with the arrangement patterns of the cylinders.
  • Atsuhide Kitagawa, Yuichi Murai, Masaaki Ashihara, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 68 670 1637 - 1645 2002年 [査読有り][通常論文]
     
    In the first report, the two-dimensional bubble-bubble interaction of wall-sliding bubbles is captured by using Particle Tracking Velocimetry. In this report, trial studies to introduce the bubble-bubble interaction into Eulerian-Lagrangian model have been performed. Firstly, the bubble-bubble interaction force vector is estimated by inverse analysis from experimental results. The translational motion equation of a bubble is used to derive the interaction force vector. Secondly, two kinds of interaction models are proposed and applied to the numerical simulation. Comparison between the simulated and experimental results revealed that the introduction of the bubble-bubble interaction model enabled to predict much more accurate structure of sliding bubble motion than previous Eulerian-Lagrangian model.
  • Atsuhide Kitagawa, Masaaki Ashihara, Yuichi Murai, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 68 668 1111 - 1118 2002年 [査読有り][通常論文]
     
    The bubble-bubble interaction in a swarm of wall-sliding bubbles is experimentally investigated using an image processing measurement. At first, the drag coefficient of a vertically sliding bubble is measured for the range of Reynolds number from 2 to 9. Secondly, the two-dimensional pattern of the bubble-bubble interaction in a layer of wall sliding bubbles is detected by using particle tracking velocimetry (PTV). The evolution of relative coordinates and the relative velocity vectors of the bubbles are clarified by the statistical data analysis. Also, hydrodynamic mechanism of the bubble-bubble interaction is discussed with the present data comparing literatures on twin bubble interactions.
  • Junichi Ohta, Atsushi Shozude, Yuichi Murai, Fujio Yamamoto
    Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 68 668 1095 - 1103 2002年 [査読有り][通常論文]
     
    This paper describes the gas-liquid interface shape and the internal flow field of a liquid bridge that is placed to bridge the cross-section of a horizontal narrow rectangular converging channel made of glass with a gap size of 1.2 mm and a converging angle of 2.97°. Such a liquid bridge is moved to the smaller cross-section by surface tension. Liquid bridge are observed and transported in semi-scale channels and also in gas-liquid separator under a microgravity condition. Thus, it is important to understand the liquid bridge behavior from point of view of semi-scale flows dominated by surface tension. In the present study, a liquid bridge made of ethyl alcohol or mixture of water and ethyl alcohol as the liquid was viewed from the top and the side. (1) The internal flow fields of the liquid bridge in the side view were quantitatively measured by the brightness distribution cross-correlation method, i.e. PIV (Particle Imaging Velocimetry). (2) The gas-liquid interface shape was expressed using Fourier factors, and the feature was clarified. (3) Effects of various parameters on the liquid bridge behavior were examined.
  • A Kitagawa, Y Murai, F Yamamoto
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 27 12 2129 - 2153 2001年12月 [査読有り][通常論文]
     
    Eulerian-Lagrangian approaches for dispersed multiphase flows can simulate detailed flow structures with a much higher spatial resolution than the Eulerian-Eulerian approaches. However, there are still unsolved problems regarding the calculation method for accurate two-way interaction, especially on the numerical instability due to the dispersion migration through discrete computational grids. Inadequate solvers sometimes produce false velocity fluctuation which makes the simulation unstable. In this paper, a new calculation method for dispersion-to-continuous phase interaction, which is accompanied by spherical dispersion migration, is proposed. The basic principle of the method is the introduction of Lagrangian filtering functions which convert discrete dispersion volume fractions to a spatially differentiable distribution. The performance of linear, Gaussian and sinewave filtering functions is examined by simple benchmark tests and applied to the simulation of dispersion-generated fluctuation. Using the present method, three-dimensional continuous phase flow structures induced by rising spherical bubbles and/or settling solid particles are demonstrated. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • LP Shen, XQ Song, Y Murai, M Iguchi, F Yamamoto
    FLOW MEASUREMENT AND INSTRUMENTATION 12 3 191 - 199 2001年06月 [査読有り][通常論文]
     
    This paper describes a method for simultaneously measuring the velocities and sizes of falling particles. The measurement method consists of two parts. One is the recognition of the particles from a raw image by an image-processing technique in order to obtain the sizes and positions of the particles, and the other is a measurement technique of Particle Tracking Velocimetry based on fuzzy logic for the falling velocities of particles. The method is examined by a numerical experiment with computer-generated images. The result shows that the present method can be applied on-line for real-time processing of practical measurements. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • Quantitative Understanding of Bubble-Bubble Interaction Dynamics Enabled by Application of Particle Tracking Velocimetry
    Y. Murai, M. Ashihara, M. Ishikawa, A. Kitagawa, F. Yamamoto
    DLR-Mitteilung 3 1113 - 1120 2001年 
    Bubble-bubble interaction is a quite fundamental issue to understand multiphase flow dynamics and to improve mathematical models of dispersed multiphase flow for higher dispersion volume fraction. In this study, two-dimensional particle tracking velocimetry (PTV) is applied to the measurement of wall-sliding bubbles whose motions are governed by the bubble-bubble interaction. Only PTV enables the measurement while PIV based on cross correlation does not determine exact motion of the individual bubbles. Also, the PTV is improved in solving more accurate center of gravity of the bubbles in order to measure the velocity component of the bubble-bubble interaction whose magnitude is an order of a few % as the terminal rising velocity. More than 100,000 velocity vectors of the bubbles are used to calculate the average bubble-bubble interaction pattern in each case during the void fraction and Reynolds number are varied in the range from 0 .00 to 0.15 and 1-100, respectively.
  • Particle Tracking Velocimetry for Dispersions in Multiphase Flows
    F. Yamamoto, Y. Murai, M. Ishikawa
    DLR-Mitteilung 3 433 - 438 2001年 
    PIV and PTV are quite useful tools for measuring dispersed multiphase flows because of possibility of field measurement that provides a lot of information on the dispersion. However, simple application of conventional technique involves several risks of misunderstanding the multiphase flow structure. In this paper, the important differences between tracer particles in single phase flow and dispersions in multiphase flow are discussed through our experience.
  • Y Murai, Y Matsumoto, F Yamamoto
    EXPERIMENTS IN FLUIDS 30 1 11 - 21 2001年01月 [査読有り][通常論文]
     
    A method for measuring the instantaneous 3-D bubble distribution in bubbly flows is proposed by making use of stereoscopic image processing. The method applies to the case of higher rather than dilute void fractions, because it is based on the following two statistic-based procedures. The first process is to obtain the 2-D distribution of local void fraction from visualized images, where a correlation between the bubble shadow fraction and the projection void fraction is derived by introducing the new idea of overlapping probability of the bubble-images under various conditions. The second process is to reconstruct the 3-D distribution of the local void fraction. In this step, a logical method is proposed in order to obtain the bubble-existence probability function which simultaneously satisfies the two distributions of the two projection void fractions. The present method is applied for instantaneous measurement of the 3-D structure of a bubble plume. The measured results show its particular structure, such as the hollow distribution of the bubbles, and the local spiral structure, which cannot be captured by point-measurement experiments.
  • 笹木 俊男, 村井 祐一, 山本 富士夫
    年次大会講演論文集 1 271 - 272 一般社団法人日本機械学会 2001年 
    Bubbles in a particle sedimentation layer has quite irregular and complicated phenomena due to frequent collision between the bubbles and the particles. This paper shows our trial to find out the fundamental characteristics of the bubble behavior using two approaches. One is two dimensional experimental visualization using image analysis to capture the bubble trajectories. Another is numerical simulation considering the bubble-particle collision. These results reveal the particle clustering structure and the bubble's bouncing phenomenon.
  • 漁野 嘉昭, 村井 祐一, 山本 富士夫
    年次大会講演論文集 1 289 - 290 一般社団法人日本機械学会 2001年 
    Bubble plume will generate a high-speed and thin surface flow with wide area in sea, lake, and dam. The surface flow has a function to damp the wave motion due to the interaction with rotational motion of the waves. This study concerns with the interaction mechanism based on numerical simulation using the Eulerian-Lagrangian model. This paper shows parametric relationship for the wave damping effect between the wave form and the gas injection condition.
  • 石川 正明, 村井 祐一, 山本 富士夫
    年次大会講演論文集 1 195 - 196 一般社団法人日本機械学会 2001年 
    A lot of PIV algorithm has been dealt with a translation motion. Therefore, error vectors are obtained for strong deformed flows. Nowadays, recursive processes of a cross-correlation PIV and a gradient-based PIV are used as the control of the influence of strong deformed flows. However, these recursive processes do not correspond to strong deformed flows perfectly. In this study, unknown valuables of the gradient-based method including the velocity gradient tensor are employed because of overcoming of strong deformed flows. The performance of a recursive gradient-based method is estimated by a simulation of a Taylor-Green vortex flow.
  • 北川 石英, 石川 正明, 村井 祐一, 山本 富士夫
    年次大会講演論文集 1 101 - 102 一般社団法人日本機械学会 2001年 
    The microscopic flow containing bubbles and solid particles shows complicated behavior but it sways performance of material surface characteristics in fluid machineries and environmental devices. This paper shows simulation technique for the dispersed three-phase flow and the application results for induction flow in the vicinity of a wall with arrangement of rectangular obstacles. Parametric study has been done and revealed that the probability of bubble-capturing in a cavity flow between the obstacles was higher than that of particle.
  • ハッサン アブダルモウティ, 村井 祐一, 大野 泰, 山本 富士夫
    可視化情報学会論文集 21 2 31 - 37 社団法人 可視化情報学会 2001年 
    気泡プルームは，気泡の浮力に伴って大規模な自然対流を駆動する輸送現象の一つとして知られる．この気泡プルームによって発生する表面流は，港湾施設，河川，湖畔を保護するために活用されている．しかしながら過去において，表面流発生過程の詳細なメカニズムを実験的に計測した例は殆どない．本論文は，気体流量，気泡サイズ，ならびに気泡プルームの内部流動構造に依存した表面流の特性を報告するものである．計測データは PIV（粒子画像処理流速計）を三種類の可視化画像に適用することで得られた：第一に気泡プルームまわりの全流動，第二に表面流，第三に，自由表面下の表面流発生領域の可視化である．この結果，本実験で取り扱った実験範囲に関しては，表面流の最大速度が気体流量の 0.25～0.45乗に，気泡直径の -0.25～-0.75乗に比例することなどが判った．また，表面流の付加的機能として，消波効果についても検討を行った．
  • 北川 石英, 村井 祐一, 山本 富士夫
    混相流 = Japanese journal of multiphase flow 14 4 442 - 450 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2000年12月15日 
    It is known that the Eulerian-Lagrangian approaches for dispersive multiphase flows can simulate detailed flow structures with a much better spatial resolution than the Eulerian-Eulerian approaches. However, there are still unsettled problems regarding the calculation method for two-way interaction. Especially, numerical instability due to the dispersion's migration beyond computational mesh is a serious issue for accurate prediction of flow instability in multiphase systems as well as multiphase turbulent flows. This paper describes revised methods for calculating the continuous phase flow which is induced by the spherical dispersion's migration. Basic principle of the methods are of introduction of template functions which convert discrete mass and momentum sources of the dispersion to spatially continuous sources. Performance of Gaussian and sine wave's template functions are examined and good pridictionability of local two way interaction have been confirmed.
  • Y Murai, Y Matsumoto
    JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME 122 4 754 - 760 2000年12月 [査読有り][通常論文]
     
    The whole behavior and the mic ro scale flow characteristics of a three-dimensional bubble plume are investigated numerically. The bubble plume drives liquid convection in a rank due to strong local two-phase interaction so that the Eulerian-Lagrangian model is formulated with emphasis on the translational motions of the bubble. In this model, each bubble motion is tracked in a bubbly mixture which is treated as a continuum. The three-dimensional numerical results reveal several particular structures, such as swaying and swirling structures of the bubble plume. These simulated flow structures show qualitatively good agreement with the experimental observations. Furthermore, the detailed behavior in the bubble plume is clarified by various analysis to discuss the dominant factors causing such the strong three-dimensionality.
  • M Ishikawa, Y Murai, F Yamamoto
    MEASUREMENT SCIENCE AND TECHNOLOGY 11 6 677 - 684 2000年06月 [査読有り][通常論文]
     
    Particle tracking velocimetry (PTV) has recently been recognized as quite an effective engineering research tool for understanding multi-dimensional fluid flow structures. There are, however, still a number of unsettled problems in the practical use of PTV, i.e. the lack of generality of the PTV algorithm for various types of flows and the measurement uncertainty with respect to spatial resolution. The authors have developed a generalized PTV algorithm named the velocity gradient tensor (VGT) method in order to accurately track the tracer particles in a flow held with strong local deformation rates. The performance of the VGT method has already been examined for several simple flow fields, such as linear shearing and Taylor-Green vortex flows. In this paper, the applicability of the VGT method for complicated flows, which include a wide dynamic range in wavenumber, is quantitatively examined by simulation of Rankine vortex flows, Karman vortex-shedding flows around a rectangular cylinder and homogeneous turbulent flows, which are numerically solved by using the unsteady Navier-Stokes equations. The results show that the VGT technique, using only two frames to estimate velocity, performs better than does the four-frame PTV technique and has a remarkably higher tracking performance than those of typical conventional PTV algorithms.
  • Y Murai, A Kitagawa, XQ Song, J Ohta, F Yamamoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 43 2 197 - 205 2000年05月 [査読有り][通常論文]
     
    The inverse energy cascade in bubbly flow is investigated by a numerical simulation using the Eulerian-Lagrangian model in which the governing equations are formulated with emphasis on the translational motion of bubbles in nonuniform flow. In this paper we are concerned with the validation of the numerical model and various parametric dependencies on the inverse cascade. The calculated results reveal that, 1) continuous growth of the spatial fluctuation scale in a bubble-induced flour is well predicted by the present numerical model and the results have a good analogy with the experimental results which were introduced in our first report, 2) the strong relationship between energy-decaying process and bubble-bubble distance interval is also identified by the present analysis, and 3) the slope of energy-decaying in the high wavenumber region depends on the kinematic viscosity of liquid, and that in the low wavenumber region depends on inhomogeneous buoyancy distribution which changes due to the bubble motion.
  • Y Murai, XQ Song, T Takagi, M Ishikawa, F Yamamoto, J Ohta
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 43 2 188 - 196 2000年05月 [査読有り][通常論文]
     
    The inverse energy cascade, which is one of the important phenomena to enhance the large-scale flow instability in bubbly flow, is investigated by measuring a local two-phase flow structure driven by buoyant bubbles using particle imaging velocimetry (PIV). In PIV, the flow field of liquid phase is measured by separating an original image to respective phase images using a statistical thresholding method for separating image parameters of bubbles and particles. The present results obtained in the case where the bubble Reynolds number and average void fraction are less than 30 and 1.5%, respectively, confirm the large energy decay with a slope index steeper than - 5/3 in the log-log diagram of energy spectrum in a high wavenumber region. An important relationship between the energy spectrum and the bubble-bubble interval distance is also detected.
  • Y Murai, Y Matsumoto, XQ Song, F Yamamoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 43 2 180 - 187 2000年05月 [査読有り][通常論文]
     
    The turbulence structure in a rising bubbly flow driven by bubble buoyancy has been analyzed using the Eulerian-Lagrangian model. ii new method of calculating the two-way interaction between the dispersed bubbles and the liquid phase was proposed to accurately simulate the local fluctuations of liquid flow induced by bubble migration. The present two-dimensional simulation revealed that, (1) in the case of the larger bubble, the turbulence structure has the longer wavelength in the vertical direction, and, (2) the wave spectrum of kinetic energy of the liquid phase is sensitive to the average void fraction and the lift force of the bubbles.
  • 山本 富士夫, 村井 祐一
    混相流 = Japanese journal of multiphase flow 14 1 8 - 15 THE JAPANESE SOCIETY FOR MULTIPHASE FLOW 2000年03月15日 
    Techniques for measuring velocity distribution in gas-liquid two-phase flow are important to elucidate the mechanisms of the flows in various two-phase systems, and to improve desigining industrial facilities. In this report, we focus on recent advanced techniques based on particle imaging velocimetry (PIV), which is known as a contact-free, multi-dimensional, instantaneous measurement tool. The current problems in applying the PIV to gas-liquid two-phase flows are summarized, and several examples of measured results are shown.
  • Two-Phase Flow Induced by a Bubble Plume in the Vicinity of a Free Surface
    Yuichi Murai, Yasushi Ohno, Abdul M. Hassan, Fujio Yamamoto
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 251 705 - 710 2000年 
    This paper is concerned with the fluid dynamic characteristics of a bubble plume, especially focussng on the generation of high speed surface flows at a free surface. Fundamental features of the surface flow are investigated by a numerical analysis based on the Eulerian-Lagrangian model, which is formulated with emphasis on the translational motion of bubbles. The study results in the following conclusions: 1) the effective thickness of the surface flow is much less in case of free surface than in case of non-slip condition, 2) the effective thickness of the surface flow increases when a liquid jet flow is provided instead of the bubble plume, 3) the surface flow involves a wavy fluctuation under the free surface.
  • Shen Liping, Suhara Ohki, Murai Yuichi, Yamamoto Fujio
    可視化情報学会誌 20 1 201 - 204 The Visualization Society of Japan 2000年 
    In this paper, a non-pulsating jet and a pulsating jet are researched experimentally and the experiment data are analyzed with a PTV (Particle Tracking Velocimetry) method. The velocity fields are measured accurately and efficiently with a PTV method based on fuzzy logic although the strong shear and turbulence appear in the jets. Based on the measured velocity fields, the distributions of mean velocity, mean vorticity, shear strain rate and kinetic energy are compared between non-pulsating and pulsating jets in order to analyze the different flow features between the two kinds of flow fields.
  • 石川 正明, 井戸 健敬, 村井 祐一, 山本 富士夫
    可視化情報学会誌 20 79 365 - 372 The Visualization Society of Japan 2000年 
    The authors developed the velocity gradient tensor method (VGT) which was a PTV algorithm for measuring flow field as reported in a previous paper. When the VGT method is used, both the velocity vector and velocity gradient tensor can be obtained at each particle point. The purpose of this study is to propose a new technique for post-processing using the velocity gradient tensor in order to make a rearrangement of velocity vectors at particle points into those at grid points with a high spatial resolution. The per-formance of the processing method is examined by the vortex flow. It is made clear that the present method has high accuracy compared to conventional interpolation methods.
  • 南 友和, 村井 祐一, 藤元 宏一, 山本 富士夫
    年次大会講演論文集 2000 461 - 462 一般社団法人日本機械学会 2000年 
    A peculiar two-phase convection is generated when an object is inserted in a free rising bubbly flow. This paper is concerned with an experimental method to elucidate the bubble behavior around several types of the object based on flow visualization and image processing techniques. Experimental results show the following points; 1) area of single-phase region behind the object depends sensitively on the shape of the object, 2) when many objects are arranged, the single-phase region expands behind the most downstream object.
  • 大野 泰, 村井 祐一, 増田 頼保, 西村 多倶磨, 山本 富士夫
    年次大会講演論文集 2000 5 - 6 一般社団法人日本機械学会 2000年 
    Monument-types of savonius windmills designed by combining art sence and windmill technology are produced by the PROD cooperative companies. The "art-oriented" Savonius windmills have been installed in many public sites such as musiums, schools, stations and sight-seeing spots because of its good harmony with natural environment and cities. This report shows a first trial of numerical analysis of flow field around the "art-oriented" windmill. The numerical method is based on incompressible Navier-Stokes equations using Lagrangian markers which express the complex boundary conditions of rotating windmill blades.
  • 太田 淳一, 須原 大, 村井 祐一, 井口 学, 水野 義照, 山本 富士夫
    年次大会講演論文集 2000 99 - 100 一般社団法人日本機械学会 2000年 
    This paper describes the turbulent flow characteristics of axisymmetric non-pulsating and pulsating jets measured by PIV (Particle Imaging Velocimetry). The PIV measurement is made for a pulsating jet at an amplitude ratio of 0.25,a Strouhal number St of 0.17,and a Reynolds number of 1070. According to the measured velocities, the fluid motions are classified into four quadrant categories, i.e. ejection, outward interaction, sweep, and inward interaction. The contributions of these classes of motion to frequency are analyzed. The present result at St=0.17 and a dimensionless distance of z^^-=4 is different from the previous one measured at St=7.8×(10)^<-4> and z^^-=20. It is clear that the frequency of ejection is dominant and the frequencies of the inward interaction and the sweep become approximately equal for phases just after passing the maximum velocity.
  • Yuichi Murai, Takehiro Ido, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 66 649 2265 - 2273 2000年 [査読有り][通常論文]
     
    In the first report, improved post-processing algorithms, which rearrange discrete velocity vectors obtained by PTV better into regular grid spaces, were proposed. The present report deals with extensions of the methods to time serial processing and to the detection of mis-matched vectors. The performance of these algorithms are evaluated by using the flow around a rectangular cylinder and a vortex flow. Furthermore, the actual advantages of using these methods are discussed by applying them to the experimental result of sudden vortex generation due to the collision of a circular cylinder with a flat wall. © 2000, The Japan Society of Mechanical Engineers. All rights reserved.
  • Atsuhide Kitagawa, Yuichi Murai, Junichi Ohta, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 66 642 323 - 331 2000年 [査読有り][通常論文]
     
    This paper is concerned with a numerical method and its application to the prediction for turbulence structure which is induced in three-phase flows containing bubbles and particles. The Eulerian-Lagrangian model for three-phase flows has been constructed since the mathematical validity of the model was confirmed for bubbly two-phase flow in previous papers. Two-and three -dimensional predictions were carried out and provided detailed phenomenological information on three-phase interaction processes. When the bubble and the particle volume fractions were less than 5%, generation of kinetic energy was reduced more in three-phase flow than in two-phase flow, because of decrease in body force spectrum. Especially, the turbulence with long wave length was not strongly grown because of cancelation of meso-scale body force due to local dispersion of the bubbles and the particles. Resultant slope of energy spectrum in high wavenumber region became much calmer than the similar phenomena in bubbly two-phase flow cases.
  • Yuichi Murai, Koichi Fujimoto, Toru Ishiguro, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 66 646 1273 - 1280 2000年 [査読有り][通常論文]
     
    An experiment showed a quite strong effect of inserting a circular cylinder into a unform rising bubbly flow. Size of the effected zone was more than several times as that of the cylinder. The purpose of present study is to elucidate the mechanism of generating the two-phase convection using a numerical analysis based on Eulerian-Lagrangian model by which the bubble's boundary condition on the cylinder can be treated accurately. The numerical results showed a good agreement with the experimental results and revealed the dependency of the flow on the void fraction, bubble radius, blockage ratio as well as the bubble's bouncing condition on the cylinder surface.
  • M. Ishikawa, Y. Murai, A. Wada, M. Iguchi, K. Okamoto, F. Yamamoto
    Experiments in Fluids 29 6-6 519 - 531 2000年 [査読有り][通常論文]
     
    Most particle-tracking velocimetry (PTV) algorithms are not suitable for calculating the velocity vectors of a fluid flow subjected to strong deformation, because these algorithms deal only with flows due to translation. Accordingly, it is necessary to develop a novel algorithm applicable to flows subjected to strong deformations such as rotation, shear, expansion and compression. This paper proposes a novel particle tracking algorithm using the velocity gradient tensor (VGT) which can deal with strong deformations and demonstrates that this algorithm is applicable to some basic fluid motions (rigidly rotating flow, Couette flow, and expansion flow). Furthermore, the performance of this algorithm is compared with the binary image cross-correlation method (BICC), the four-consecutive-time-step particle tracking method (4-PTV), and the spring model particle tracking algorithm (SPG) using simulations and experimental data. As a result, it is shown that this novel algorithm is useful and applicable for the highly accurate measurement and analysis of fluid flows subjected to strong deformations.
  • Y. Murai, Y. Matsumoto, F. Yamamoto
    Journal of Visualization 3 1 27 - 35 2000年 [査読有り][通常論文]
     
    Overall, as well as individual, bubble behavior of a plane bubble plume which is confined by two parallel plates is investigated by means of several qualitative and quantitative flow visualization methods. These include observation, measurement of time-averaged void distribution, surface tufts and particle imaging velocimetry. Several kinds of unstable motion of the bubble convection, which depend on the free surface initial height and on the gas flow rate, are observed. The bubble motion along the bubble plume is precisely measured by an image-processing method which also delivers velocity vectors, number density and size of the bubbles.
  • K Miyazaki, G Chen, F Yamamoto, J Ohta, Y Murai, K Horii
    EXPERIMENTAL THERMAL AND FLUID SCIENCE 19 4 194 - 203 1999年08月 [査読有り][通常論文]
     
    With a concise review on some basic and novel algorithms and methods for the techniques of particle-imaging velocimetry (PIV), the paper reports an application of the PIV techniques to the investigation of particle motion in a gas-solid two-phase spiral flow in a horizontal tube. Axial velocities of the transported particles are obtained. Some important features of particle motion governing high transportation efficiency of the spiral flow are revealed by investigating probability density distribution of particle locations in a pipe cross-section. (C) 1999 Elsevier Science Inc. All rights reserved.
  • Song, X, F Yamamoto, M Iguchi, Y Murai
    EXPERIMENTS IN FLUIDS 26 4 371 - 380 1999年03月 [査読有り][通常論文]
     
    A new algorithm of Delaunay Tessellation Particle Tracking Velocimetry (DT-PTV in abbreviation) is proposed for tracking particles in images of a PIV system by making use of the Delaunay tessellation (DT). The algorithm is tested by using numerically simulated particle images. The calculation results based on DT are compared with those obtained by a conventional algorithm of Binary Image Cross-correlation method (BICC). The new algorithm shows higher performance of obtaining more identical particles in two consecutive images correctly with shorter computation time even if the images contain many particles. A further application of DT to elimination of spurious vectors is also discussed.
  • Song, X, F Yamamoto, M Iguchi, H Kato, Y Murai, K Ishii, Y Sasaki
    ISIJ INTERNATIONAL 39 5 471 - 476 1999年 [査読有り][通常論文]
     
    The number of particles passing through the whole field of interest in a unit lime, referred to as the articles particle number rate, cannot be measured accurately and easily by the conventional methods when the number density of particles is high. However, there are many demands for whole field measurement of the particle number rate in various industrial processes. The purpose of the present investigation is to develop a new method for measuring the particle number rate by introducing PIV (Particle Imaging Velocimetry). In the present work, particles coming out of a hopper, and then falling in air or water were treated. Images of the falling particles were taken by a high speed video camera. Particle velocities were measured by the PIV based on the Binary Image Cross-Correlation Method (BICC), and the particle number rate crossing a plane could be computed from the mean velocity of particles and the number of the particles in the image. The performance of the present method for measuring the particle number rate was evaluated by numerical simulations and experiments. The experimental results showed that the particle number rate of a cloud of particles could be measured with high accuracy by the newly developed methods. The measurement precision of the particle number rate depends on the number of sampling video frames. Several seconds of video frames can yield sufficient precision of the particle number rate. The present research can be applied to on-line measurement of particles in many industrial fields.
  • Eulerian Analysis of Bubbly Two-Phase Flows using CIP Scheme
    Murai,Y, Matsumoto,Y
    Computational Fluid Dynamics Journal 8 26 - 33 1999年 [査読有り][通常論文]
  • ABDULMOUTI HASSAN, 村井 祐一, 太田 淳一, 山本 富士夫
    可視化情報学会誌 19 1 239 - 242 The Visualization Society of Japan 1999年 
    Bubble curtain is expected to be a new type of oil fence because it can generate a strong and wide surface flow over the bubble generation system. However, the most suitable condition for the bubble generation system has not been investigated. In this work, the surface flow induced by the bubble curtain is measured by particle imagining velocimetry, and the parametric dependency on the gas flow rate, void fraction and bubble size have been made clear. Furthermore, the internal two-phase flow structure in the bubble curtain is discussed with the PIV measurement data.
  • 篠田 圭司, 太田 淳一, 村井 祐一, 山本 富士夫
    可視化情報学会誌 19 1 113 - 114 The Visualization Society of Japan 1999年 
    The objective of this study is to apply holography to three-dimensional location measurement of particles. We made experiments using the behind scattering beam type ofF-axis holography with an Ar-Ion Laser. We measured three-dimensional coordinates of particles as follows: Centers of gravity for the particles in a 3-D space were measured by the moment method using a stack of x-y cross-section(slice in the depth direction), y-z cross-section, and x-z cross-section images. The present method is verified. Furthermore, a reconstructed image is showed in a 3-D space.
  • 井戸 健敬, 村井 祐一, 太田 淳一, 山本 富士夫
    可視化情報学会誌 19 1 303 - 306 The Visualization Society of Japan 1999年 
    Velocity vectors obtained by PTV contain usually mis-matched vectors. In order to estimate the whole flow field structure, the mis-matched vectors should be eliminated exactly. In the present report, a method of mis-matched vector elimination in PTV based on Laplace equation rearrange-ment is proposed. As a result, it is recognized that the present method has good performance by the verification after applying it to two-dimensional vortex flow and Karman vortex flow. Furthermore, it is confirmed to acquire higher performance by using a successive iteration type.
  • 石川 正明, 村井 祐一, 太田 淳一, 山本 富士夫
    可視化情報学会誌 19 1 311 - 314 The Visualization Society of Japan 1999年 
    We have developed the velocity gradient tensor method (VGT) which is a PTV algorithm. When the VGT method is used at particle points, we can simultaneously get both of the velocity vectors and velocity gradient tensor. It means that physical information can be directly extracted at particle points. The purpose of this study is to propose a new technique of the extraction of physical information at particle points from the velocity gradient tensor. The processing is applied to the vortex flow and PIV-Standard Image, the performance is examined from the precision for extraction of vorticity and stream function.
  • HASSAN ABDULMOUTI, 村井 祐一, 太田 淳一, 山本 富士夫
    可視化情報学会誌 19 2 209 - 210 The Visualization Society of Japan 1999年 
    Bubbly flow shows complicated behavior due to a strong dynamic interaction between bubble and vortex motions. A technique for generating a strong surface flow by using a bubble curtain has been proposed by the authors. In the future, bubble curtain is expected to be a new type of oil fence because it can generate a strong and wide surface flow over the bubble generation system. The present paper is concerned with the mechanism of generating the surface flow. Furthermore, the internal two-phase flow structure of the surface flow generation induced by the bubble curtain is discussed using PIV (particle imaging velocimetry) measurement data after separating bubbles and particles from the original images.
  • 田島 カルロス, 井戸 健敬, 村井 祐一, 太田 淳一, 山本 富士夫
    可視化情報学会誌 19 2 145 - 148 The Visualization Society of Japan 1999年 
    It is well-known that the efficiency of capturing velocity vector in 3-D PTV is much lower than in 2-D PTV due to the problems in particles' occlusion, stereo-matching process, as well as the resolution of the optical hardwares. A new method for particle tracking velocimetry by using a color illumination device with only one camera has been proposed in the present paper. The information of color gradation in the depth direction is employed to determine their 3-D coordinates and velocity components. This report describes the performance of the present method, which is examined by measuring the 3-D flow field of a simple rotating flow.
  • Yuichi Murai, Jun Iwase, Fujio Yamamoto
    Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 65 638 3366 - 3373 1999年 [査読有り][通常論文]
     
    Flow induced by oscillating elastic blades in quiescent liquid is investigated using PIV (particle imaging velocimetry). Theoretical prediction and image-measurement of the bending blade motion ranging from zero to 60 Hz in frequency indicate that is has maximum amplitude in the second order resonance mode owing to large added inertia force. PIV measurement is performed to evaluate the agitation structure around the blade with order of 106 in Reynolds number which is defined using the frequency f blade length L and kinematic viscosity v y Re=fL2/v re than 600 velocity vectors are obtained between two consecutive images by using the BinarizedTmage Cross Correlation algorithm. The present results reveal generation of intermittent convection in the region downstream of the blade, that period is over 10 times as that of oscillating blade. Also, parametirc dependency of induced energy on blade-dimension and forced frequency is shown in this experiment.
  • Y Murai, Y Matsumoto
    JSME INTERNATIONAL JOURNAL SERIES B-FLUIDS AND THERMAL ENGINEERING 41 3 568 - 574 1998年08月 [査読有り][通常論文]
     
    Detailed flow structure of bubbly flours observed in a bubble plume is investigated numerically using the Euler-Lagrange model where the bubbly flow is treated as a continuum and each bubble is tracked in the flow. The governing equations are formulated with emphasis on the translational motion of the bubble in non-uniform unsteady liquid flow. Improvement of the present numerical method is confirmed by comparison with the Eulerian method, and the numerical results are validated by the comparison with the two kinds of experimental results, i.e., global flow pattern visualized by direct-lighting method, and local bubble motion measured by particle imaging velocimetry. In this paper, two-dimensional bubble plume which is confined by two parallel plates is analyzed and the parametric dependency, such as influence of the bubble size distribution and void fraction, on the whole two-phase behavior is clarified and experimental validation is conducted.
  • 井戸 健敬, 石川 正明, 村井 祐一, 山本 富士夫
    可視化情報学会誌 = Journal of the Visualization Society of Japan 17 235 - 238 The Visualization Society of Japan 1997年07月01日 
    Velocity vectors obtained by PIV are distributed discretely depending on the number density of the tracer particles seeded in the flow. In order to estimate the detailed whole-field flow structure from the data, an estimation algorithm to restore the whole-field flow has been proposed using Laplace Equation and velocity correction potential. The performance of the algorithm was examined for two-dimensional vortex flow. The correct restoration rate was evaluated quantitatively by two-dimensional correlation coefficient for the stream function. The results reveal that the present method is applicable for various conditions of discrete PIV data to predict the whole-field flow structure.
  • PIV measurement of dynamic interaction between oscillating blades and fluid flow inside a bioreactor
    Jun Iwase, Fujio Yamamoto, Yuichi Murai, Manabu Iguchi, Kimiyasu Yasuda, Naoyuki Fujii
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 13 1997年 
    This paper is concerned with the interaction of oscillating blade and the fluid flow in a fluidized bed type of bioreactor. The motion properties of blades were investigated through the experimental measurements and theoretical estimation. In the theoretical work, the blade motion was considered with the effect of virtual mass on the oscillating blade. The characteristics of the flow around oscillating blades was investigated with the PIV. The experiment was carried out in some range of the oscillation frequency. A convection waves shed from the blade tip is introduced as a new phenomenon and its behavior is investigated.
  • Numerical and experimental investigations of bursting bubble on free surface
    Toshifumi Yoshikawa, Yuichi Murai, Fujio Yamamoto
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 13 1997年 
    The `bursting bubble' phenomenon is observed in various industrial situations such as bioreactors which purify excreta using microbes, heat exchangers for nuclear power plants, and refining system of various metals. For the improvement of safety and controlability of those system, it is required to elucidate its unsteady behavior where large kinetic energy is sometimes generated by strong interaction between rising bubble and upper free surface. The purpose of present investigation is to make apparent the influences of surface tension and viscosity of liquid on the bursting structure by experimental visualization of two free surface motions and numerical simulation using the VOF method. This paper describes mainly the simulation method and the predicted results of bursting bubble structures after showing several experimental results.
  • 宋 向群, 山本 富士夫, 井口 学, MURAI Yuichi
    可視化情報学会誌 = Journal of the Visualization Society of Japan 16 19 - 22 The Visualization Society of Japan 1996年11月01日 
    In this paper, a new algorithm of particle identification based on Delaunay tessellation is proposed. Delaunay tessellation is a method which connects every scattered nodes to form triangles in either two-dimensional or three-dimensional space. Such a triangulation provides an essential step for spatial analysis of scattered data. Delaunay tessellation can be applied in PIV which deals with the particles in image. A new cross-correlation method for particle identification has been devised and tested by numerical simulation. Good result can be obtained.
  • An investigation of flows of a rotating hollow circular cylinder (When it impulsively starts rotating in a uniform flow)
    Fujio Yamamoto, Manabu Iguchi, Yuichi Murai, Gang Chen, Masahiro Ogawa
    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED 239 135 - 141 1996年 
    The particle imaging velocimetry, or PIV is applied to investigate unsteady flows inside and outside a hollow circular cylinder with impulsively starting to rotate in a uniform flow in order to obtain some fundamental data about the historical force effect and flow features. These flows are visualized by the solid particle tracer technique and analyzed using the PIV based on the two-dimensional binary image cross-correlation method in which three consecutive frames are used to detect positions of particles and to obtain particle velocity vectors. A one-dimensional unsteady model is used to analyze the flow inside the rotating hollow cylinder. For the outside flow, the velocity and pressure in the Navier-Stokes equation are solved based on control volume method in space and an implicit scheme in time. Velocity vectors, streamline patterns, lift and drag are obtained for Re=40 and rotating speed α=1.
  • 水平気液二相チャネル乱流における人工ボイド波の伝ぱ
    田中泰爾, 朴炫珍, 田坂裕司, 村井祐一
    混相流 accepted [査読有り][通常論文]

MISC

  • 田坂 裕司, 大家 広平, 芳田 泰基, 村井 祐一 ながれ : 日本流体力学会誌 = Nagare : journal of Japan Society of Fluid Mechanics 43 (2) 154 -160 2024年06月
  • 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年
  • 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年
  • 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年
  • 村井祐一, 田坂裕司, 朴 炫珍, 高野 慧, 正信 聡太郎 混相流，Vol. 36, No. 3, pp. 329-335 (2022) 36 (3) 2022年09月 [査読無し][招待有り]
  • 船体と海水の摩擦抵抗を低減する空気潤滑技術
    村井祐一, 田中泰爾, 堀本康文, 朴 炫珍, 田坂裕司 トライボロジズト, Vol. 67, No. 8, pp.547-554 (2022) 2022年08月 [査読有り][招待有り]
  • 超音波パルスエコグラフィーによる気泡流のモニタリング
    朴炫珍, 田坂裕司, 村井祐一 可視化情報学会誌, Vol.42, No.163, pp.15-18（2022) 2022年01月 [査読有り][招待有り]
  • 研究開発の俯瞰ー環境・エネルギー分野2021年版
    村井祐一, ほ JST研究開発戦略センター年次報告書 2021 2021年04月 [査読無し][招待有り]
  • 非ニュートン性流体の粘弾性は粒子の分散状態に影響されるか？
    芳田泰基, 田坂裕司, 村井祐一 日本機械学会流体工学部門ニューズレター2021 2021 (4) 2021年04月 [査読無し][招待有り]
  • 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年
  • 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年
  • 超音波による混相流用の流量計の開発
    村井祐一 油空圧技術，日本工業出版 60 1 -5 2021年01月 [査読無し][招待有り]
  • 村井祐一, 田坂裕司, 朴炫珍 日本実験力学会 20 87 -94 2020年 [査読無し][招待有り]
  • 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年
  • 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年
  • 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年
  • 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年
  • 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年
  • 気液二相乱流の超音波モニタリング
    村井祐一, 田坂裕司, 朴炫珍 可視化情報 39 11 -16 2019年09月 [査読無し][招待有り]
  • 田坂裕司, 芳田泰基, 村井祐一 ながれ 38 (4) 283‐290 2019年08月25日 [査読無し][通常論文]
  • 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年08月
  • 熊谷一郎, 熊谷一郎, 村井祐一, 川北千春, 濱田達也 混相流シンポジウム講演論文集(Web) 2019 2019年
  • 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年 [査読無し][通常論文]
  • 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年05月17日 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 李 瑞雪, 芳田 泰基, 人見 純平, 澤田 航希, 朴 炫珍, 田坂 裕司, 村井 祐一, フィッシャー ステファン 流体工学部門講演会講演論文集 2018 (0) OS4 -1 2018年 [査読無し][通常論文]
     
    <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>
  • 田坂 裕司, 芳田 泰基, 朴 炫珍, 村井 祐一 流体工学部門講演会講演論文集 2018 (0) OS4 -2 2018年 [査読無し][通常論文]
     
    <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年06月 [査読有り][通常論文]
  • 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年 [査読無し][通常論文]
  • 村井 祐一, 田坂 裕司 化学工学 80 (8) 468 -471 2016年08月
  • 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年07月 [査読無し][通常論文]
  • 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年07月 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 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年 [査読無し][通常論文]
  • 大石 義彦, 朴 〓珍, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2015 "0601 -1"-"0601-2" 2015年11月07日 
    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.
  • 横山 聡哉, 村井 祐一, 田坂 裕司, VLASKAMP Jop, DENISSENKO Peter, THOMAS Peter J. 流体工学部門講演会講演論文集 2015 "1702 -1"-"1702-2" 2015年11月07日 
    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.
  • 村井 祐一, 田坂 裕司, 大久保 順平, 大石 義彦, 竹内 智朗 流体工学部門講演会講演論文集 2015 "1703 -1"-"1703-2" 2015年11月07日 
    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.
  • 大須賀 侑, 小林 寛尭, 大石 義彦, 田坂 裕司, 村井 祐一 年次大会 : Mechanical Engineering Congress, Japan 2015 "J0510102 -1"-"J0510102-5" 2015年09月13日 
    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.
  • 塚原 塚原, 緒方 正幸, 熊谷 一郎, 大石 義彦, 酒巻 春輝, 村井 祐一 年次大会 : Mechanical Engineering Congress, Japan 2015 "J0510105 -1"-"J0510105-4" 2015年09月13日 
    We have invented a novel bubble generator with a vented hydrofoil for ship drag reduction. The hydrofoil has an air outlet on the top surface, and small air bubbles are generated by the negative pressure above the hydrofoil as the device moves forward. In order to understand the relationship between the local shear stress and the local projection void fraction under the ship hull, towing tank (100m) experiments using a 4m-long model ship made by transparent acrylic resin were conducted at Hiroshima University. The void imaging data obtained by a high-speed video camera revealed that the characteristics of the entrained bubbles (bubble size, bubble volume flux, etc.) depend on the towing velocity, angle of attack, and the arrangement of the vented hydrofoil. A large amount of air was introduced by this device when the hydrofoil was mounted at the non-inverted position with the angle of attack from 10 to 15 deg. On the other hand, the local drag reduction rate of the inverted hydrofoil setting was higher than that of the non-inverted one.
  • 小林 寛尭, 大石 義彦, 田坂 裕司, 村井 祐一, 武田 靖, WINDHAB Erich 年次大会 : Mechanical Engineering Congress, Japan 2015 "J0510104 -1"-"J0510104-5" 2015年09月13日 
    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年09月 [査読有り][通常論文]
  • Void imaging in two-phase flow for ship drag reduction
    T.Tsukahara, M.Ogata, I.Kumagai, H.Sakamaki, Y.Oishi, Y.Murai Proc. 9th International Symspoium on Measurement Techniques for Multiphase Flow 65 -66 2015年09月 [査読無し][通常論文]
  • 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年07月 [査読有り][通常論文]
  • Flow visualization around bubble generating hydrofoils
    T.Tsukahara, M.Ogata, Y.Oishi, H.Sakamaki, Y.Murai, I.Kumagai Proc. ASME-JSME-KSME Joint Fluids Engineering Conference 2015年07月 [査読有り][通常論文]
  • 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年07月 [査読有り][通常論文]
  • 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年07月 [査読有り][通常論文]
  • 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年 [査読無し][通常論文]
  • 村井 祐一, 小林 一道 混相流 28 (4) 483 -486 2014年12月
  • 村井 祐一 Journal of the Japan Institute of Energy = 日本エネルギー学会誌 93 (11) 1038 -1043 2014年11月 
    Injection of small bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. In the case of small bubbles, drag reduction occurs with their unique dynamic characteristics in turbulence. One of them is highlighted by significant viscoelasticity in clustered microbubbles that appears in the high-enstrophy regions in turbulence. Also, deformability of small bubbles subject to strong shear suppresses surrounding turbulence so that friction decreases. Based on these physics, several applications to ship drag reduction are introduced, which realized about 10% fuel saving with small bubbles as they were suitably supplied on the ship hulls.
  • Ultrasonic measurement of bubble motions in a wall boundary layer.
    H-J.PARK, Y.OISHI, Y.TASAKA, Y.MURAI 2014 HU-SNU Symposium on Mechanical and Aerospace Engineering. 53 2014年11月 [査読無し][通常論文]
  • 大石 義彦, 田坂 裕司, 村井 祐一, 峠 幸寛 流体工学部門講演会講演論文集 2014 "0215 -1"-"0215-2" 2014年10月25日 
    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
  • 塚原 嵩博, 濱 紀子, 熊谷 一郎, 緒方 正幸, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2014 "0213 -1"-"0213-2" 2014年10月25日 
    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.
  • 田坂 裕司, 中島 平裕, 村井 祐一, 大石 義彦 流体工学部門講演会講演論文集 2014 "0520 -1"-"0520-2" 2014年10月25日 
    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.
  • 村井 祐一, 北浦 秀和, 田坂 裕司, 城野 清治 流体工学部門講演会講演論文集 2014 "0205 -1"-"0205-2" 2014年10月25日 
    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.
  • 横山 聡哉, 村井 祐一, 大石 義彦, 田坂 裕司, 武田 靖 年次大会 : Mechanical Engineering Congress, Japan 2014 "J0540301 -1"-"J0540301-4" 2014年09月07日 
    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.
  • 小林 寛尭, 小田 友郎, 大石 義彦, 田坂 裕司, 村井 祐一 年次大会 : Mechanical Engineering Congress, Japan 2014 "J0510202 -1"-"J0510202-5" 2014年09月07日 
    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.
  • 小田 友郎, 大石 義彦, 田坂 裕司, 村井 祐一 年次大会 : Mechanical Engineering Congress, Japan 2014 "J0510201 -1"-"J0510201-5" 2014年09月07日 
    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.
  • 田坂裕司, 渡村友昭, 朴炫珍, 村井祐一, 大石義彦 化学工学会 78 593 -596 2014年09月 [査読無し][招待有り]
  • 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年08月 [査読無し][通常論文]
  • 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年08月 [査読有り][通常論文]
  • 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年08月 [査読有り][通常論文]
  • 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年08月 [査読有り][通常論文]
  • 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年06月 [査読有り][通常論文]
  • 中島 平裕, 大石 義彦, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2013 "0623 -01"-"0623-02" 2013年11月09日 
    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.
  • 朴 〓珍, 大石 義彦, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2013 "0312 -01"-"0312-04" 2013年11月09日 
    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.
  • 村井 祐一, 粥川 弘英, 北浦 秀和, 大石 義彦, 田坂 裕司, 城野 清治 流体工学部門講演会講演論文集 2013 "0202 -01"-"0202-02" 2013年11月09日 
    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.
  • 山内 秀明, 宮城島 圭人, 熊谷 一郎, 大石 義彦, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2013 "0201 -01"-"0201-02" 2013年11月09日 
    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_.
  • 粥川 弘英, 朴 〓珍, 大石 義彦, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2013 "0214 -01"-"0214-02" 2013年11月09日 
    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.
  • 熊谷 一郎, 酒巻 春輝, 尾崎 翼, 大石 義彦, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2013 "0215 -01"-"0215-02" 2013年11月09日 
    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.
  • 平井 健太, 熊谷 一郎, 緒方 正幸, 村井 祐一, 栗田 敬 流体工学部門講演会講演論文集 2013 "0205 -01"-"0205-02" 2013年11月09日 
    We report a series of experimental study on the flow behavior of a buoyant jet in a non-Newtonian fluid with gel beads. A viscous fluid is supplied from a nozzle at a constant volume flux in the gel beads layer. The hydrogel beads are deformable and the volume fraction of the interstitial fluids is about 15%. In our experiments, we identify at least three types of fluid flow: homogeneous permeable flow, pulsating flow, and localized continuous flow. The flow behavior depends on the injection flow rate, the rheological properties of the mixture, and the volume fraction of the interstitial fluid. Our experimental model explains the origin of the intermittent nature of multiphase flow observed in food industries and magma transport in nature.
  • Characterization of Viscoelasticity from Complex Flows with Shear and Extension
    T.SHIRATORI, Y.OISHI, Y.TASAKA, Y. MURAI The 12th International Symposium on Fluid Control, Measurement and Visualization (FLCOME2013) OS8-04-2, USB 2013年11月 [査読有り][通常論文]
  • 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年09月16日 
    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.
  • 小田 友郎, 大石 義彦, 田坂 裕司, 村井 祐一 年次大会 : Mechanical Engineering Congress, Japan 2013 "J054012 -1"-"J054012-5" 2013年09月08日 
    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.
  • 村井 祐一, 小田 友郎, 大石 義彦, 田坂 裕司 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2013 (18) 29 -30 2013年06月19日 
    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
  • 熊谷 一郎, 酒巻 春輝, 田坂 裕司, 大石 義彦, 村井 祐一 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2013 (18) 187 -188 2013年06月19日 
    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.
  • 宮城島 圭人, Denisenco Petr, 熊谷 一郎, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2012 215 -216 2012年11月16日 
    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.
  • 村井 祐一, 熊谷 一郎, 田坂 裕司, 大石 義彦, 大薮 剛志 流体工学部門講演会講演論文集 2012 223 -224 2012年11月16日 
    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.
  • 熊谷 一郎, 村井 祐一, 田坂 裕司, 渡村 友昭, 栗田 敬 流体工学部門講演会講演論文集 2012 213 -214 2012年11月16日 
    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.
  • 大石 義彦, 峠 幸寛, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2012 221 -222 2012年11月16日 
    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.
  • 竹内 智朗, 鳥海 良一, 田坂 裕司, 熊谷 一郎, 村井 祐一 流体工学部門講演会講演論文集 2012 237 -238 2012年11月16日 
    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.
  • 大石 義彦, 村井 祐一, 田坂 裕司 北海道支部講演会講演概要集 2012 (51) 85 -86 2012年10月20日
  • 村井 祐一, 田坂 祐司, 大石 義彦, 高橋 義明 北海道支部講演会講演概要集 2012 (51) 97 -98 2012年10月20日
  • 佐藤 慧弥, 熊谷 一郎, 大石 義彦, 田坂 祐司, 村井 祐一 北海道支部講演会講演概要集 2012 (51) 95 -96 2012年10月20日
  • 村井 祐一 日本機械学會誌 = Journal of the Society of Mechanical Engineers 115 (1127) 688 -690 2012年10月05日
  • 湯本 健明, 渡村 友昭, 田坂 裕司, 熊谷 一郎, 村井 祐一 年次大会 : Mechanical Engineering Congress, Japan 2012 "J055022 -1"-"J055022-5" 2012年09月09日 
    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.
  • 熊谷 一郎, Davaille Anne, 栗田 敬, 村井 祐一 年次大会 : Mechanical Engineering Congress, Japan 2012 "J055014 -1"-"J055014-4" 2012年09月09日 
    Fluid dynamics of thermo-chemical plumes in viscous fluids was investigated. Flow pattern, temperature and compositional fields were quantitatively visualized by microcapsules of thermo chromic liquid crystals, fluorescent dye, and a laser light sheet. The behavior of thermo-chemical plumes depends on the initial buoyancy ratio B_0, which is the ratio of the stabilizing chemical buoyancy to the destabilizing thermal buoyancy at the onset of convection, and also on time. For intermediate B_0, the interplay between the thermal and compositional effects generates complicated behaviors. Because all hot plumes cool by thermal diffusion as they rise, a chemically composite thermal plume eventually attain a level of neutral buoyancy, and a secondary plume is generated from the tip of the chemical dome, then at which it begins to collapse. The thermo-chemical blob is refueled after the falling process because heat flux of the heater is constant in our experiment. Here we describe the oscillation behavior of the thermo-chemical plumes for the intermediate B_o based on the results of the heat flux by the thermo-chemical plumes.
  • 村井 祐一, 井戸 健敬 年次大会 : Mechanical Engineering Congress, Japan 2012 "J055021 -1"-"J055021-5" 2012年09月09日 
    How richly can we derive flow information from sparsely discrete velocity vector data? The problem is encountered at many situations in flow measurement from microbiological to meteorological scales. Conventional local interpolations such as Shepard and spline techniques provide visually smooth vector field, however, their spatial and temporal derivatives are mostly useless for quantitative assessment of the flow structure. Ellipsoidal interpolation developed by the authors overcome the problem since it enables global interpolation that deals velocity vector data as randomly distributed discrete boundary conditions. In this paper, reconsideration of the mathematical background and recent applications to fluid dynamics researches are reported.
  • 大薮 剛志, 熊谷 一郎, 田坂 裕司, 村井 祐一 北海道支部講演会講演概要集 2011 (50) 95 -96 2011年10月01日
  • 武島 幸太郎, 田坂 裕司, 村井 祐一, 武田 靖 北海道支部講演会講演概要集 2011 (50) 99 -100 2011年10月01日
  • 湯本 健明, 渡村 友昭, 田坂 裕司, 村井 祐一 北海道支部講演会講演概要集 2011 (50) 97 -98 2011年10月01日
  • 中島 平裕, 武島 幸太郎, 田坂 裕司, 村井 祐一 北海道支部講演会講演概要集 2011 (50) 109 -110 2011年10月01日
  • 白鳥 貴久, 熊谷 一郎, 田坂 裕司, 村井 祐一 北海道支部講演会講演概要集 2011 (50) 105 -106 2011年10月01日
  • 相川 祐輝, 白鳥 貴久, 田坂 裕司, 村井 祐一, 宮城 直樹 年次大会 : Mechanical Engineering Congress, Japan 2011 "J055015 -1"-"J055015-5" 2011年09月11日 
    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.
  • 熊谷 一郎, 大薮 剛志, 櫛田 崇文, 村井 祐一, 田坂 裕司, 高橋 義明 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2011 (16) 191 -192 2011年06月22日 
    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.
  • 村井 祐一, 田中 大樹, 繁富 啓嗣, 武島 幸太郎, 田坂 裕司, シン ウエン 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2011 (16) 355 -358 2011年06月22日 
    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.
  • 村井 祐一, 奈良林 直, 渡部 正夫 混相流 = Japanese journal of multiphase flow 25 (1) 60 -63 2011年03月15日
  • 桜井 康介, 田坂 裕司, 村井 祐一, シュミット フィリップ, フィッシャー ステファン, パラレ アン 北海道支部講演会講演概要集 2010 (49) 91 -92 2010年11月07日
  • 田中 大樹, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2010 53 -54 2010年10月29日 
    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.
  • 南部 優一, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2010 571 -572 2010年10月29日 
    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.
  • 田坂 裕司, 村井 祐一, 飯間 信 流体工学部門講演会講演論文集 2010 521 -522 2010年10月29日 
    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.
  • 白鳥 貴久, 田坂 裕司, 村井 祐一 流体工学部門講演会講演論文集 2010 465 -466 2010年10月29日 
    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.
  • 村井 祐一 流体工学部門講演会講演論文集 2010 601 -602 2010年10月29日 
    An effective utilization of non-flow-tracing particles such as small bubbles in liquid and small soap bubble in air is proposed as an extension of application in PIV and PTV. The method is composed of inverse analysis of the equation of transverse motion and interpolation of scattered velocity data in spatio-temporal domain, which enables unsteady flow field to be reconstructed.
  • 武田 靖, 田坂 裕司, 村井 祐一 化学工学 = Chemical engineering 74 (8) 381 -384 2010年08月05日
  • 大浅 浩一, 相馬 定廣, 田坂 裕司, 村井 祐一 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2010 (15) 1 -2 2010年06月20日 
    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.
  • シャムシドニア ハミドレザ, 武田 靖, 村井 祐一 日本流体力学会年会講演論文集 2010 171 -171 2010年
  • 村井 祐一, 田坂 裕司 日本流体力学会年会講演論文集 2010 159 -159 2010年 
    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.
  • 田中 大樹, 田坂 裕司, 村井 祐一, 武田 靖 北海道支部講演会講演概要集 2009 (48) 63 -64 2009年11月28日
  • 南部 優一, 田坂 裕司, 村井 祐一, 武田 靖, VLASKAMP Jozef, THOMAS Peter J. 北海道支部講演会講演概要集 2009 (48) 65 -66 2009年11月28日
  • 大山 和弥, 田坂 裕司, 村井 祐一, 武田 靖 北海道支部講演会講演概要集 2009 (48) 61 -62 2009年11月28日
  • 繁富 啓詞, 村井 祐一, 田坂 裕司, 武田 靖 北海道支部講演会講演概要集 2009 (48) 57 -58 2009年11月28日
  • 桜井 康介, 大山 和弥, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2009 427 -428 2009年11月06日 
    In order to obtain effective viscosity in bubbly liquid, which changes with transient bubble deformation, spatio-temporal velocity distributions of transient shear flows in a rotating cylinder is measured by using Ultrasonic Velocity Profiling (UVP) synchronizing of bubble deformation measurement. For Silicone oil of 1000 cSt as a test liquid, velocity distribution during spinning up has been found to be different from the liquid without bubbles. We have compared the circumferential acceleration of liquid with time serial images of bubble deformation to reach the conclusion that the maximal stretched bubbles the strongest drive the shear flow contrastively to the conventional equilibrium deformation theory of effective viscosity.
  • Jamshidnia Hamidreza, Tasaka Yuji, Murai Yuichi, Takeda Yasushi 流体工学部門講演会講演論文集 2009 523 -524 2009年11月06日 
    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.
  • 田坂 裕司, 村井 祐一, 武田 靖, 飯間 信 流体工学部門講演会講演論文集 2009 519 -520 2009年11月06日 
    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.
  • 熊谷 一郎, 中村 直哉, 村井 祐一, 田坂 裕司, 武田 靖 可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan 29 (2) 9 -10 2009年10月15日
  • 村井 祐一 可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan 29 (2) 11 -12 2009年10月15日
  • 村井 祐一, 熊谷 一郎, 田坂 裕司, 武田 靖, 高橋 義明 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) 95 -96 2009年06月28日 
    Installation of hydrofoils to ship wetted surface enables bubble generation to be realized with power consumption much lower than conventional bubble generators. With help of this principle, net effect of frictional drag reduction for ships can be improved. We have already obtained around 10% net power-saving efficiency for a cargo ferry throughout about a half year. The power-saving has a large potential to be improved more by considering multiphase fluid dynamics in terms of the hydrofoil-water-air triple interaction. In this paper, the basic principle of the bubble generation and the trial parametric studies implemented by numerical and experimental visualizations are reported.
  • 繁富 啓詞, 村井 祐一, 田坂 裕司, 武田 靖 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2009 (14) 45 -46 2009年06月28日 
    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.
  • 村井 祐一, 田坂 裕司, 武田 靖, 太田 翔子, 繁富 啓詞, 日夏 宗彦 混相流 = Japanese journal of multiphase flow 23 (1) 21 -28 2009年03月15日
  • 太田 翔子, 村井 祐一, 田坂 裕司, 武田 靖 可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan 28 (2) 95 -96 2008年09月15日
  • 大石 義彦, 村井 祐一 可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan 28 (2) 15 -16 2008年09月15日
  • 高橋 潤平, 矢野 可南子, 田坂 裕司, 村井 祐一, 武田 靖, 柳澤 孝寿, 山岸 保子 可視化情報学会誌. Suppl. = Journal of the Visualization Society of Japan 28 (2) 59 -60 2008年09月15日
  • 村井 祐一 ながれ : 日本流体力学会誌 27 (4) 321 -328 2008年08月25日 
    気泡流は大小様々な波長の現象が複合した多次元構造をもつ.このことからその実験手段には,空間構造を捉えるPIV計測がよく適合している.しかも分散体の追跡という観点で,気泡運動論とPIV解析スキームには密接なつながりがある.このためPIVツールの開発と気泡流の解明は同時並行して展開している.本稿では,気液間の双方向相互作用が流動構造を支配している自由浮上気泡流を中心として,気泡流の多重スケール構造を特徴づける実験例を紹介する.
  • 大石 義彦, BREND Mark A., THOMAS Peter J., 村井 祐一, 武田 靖 可視化情報学会誌. Suppl. 28 (1) 19 -20 2008年07月01日
  • 神田 哲志, 村井 祐一, 田坂 裕司, 武田 靖 可視化情報学会誌. Suppl. 28 (1) 17 -18 2008年07月01日
  • 村井 祐一, 山田 美幸 可視化情報学会誌. Suppl. 28 (1) 459 -460 2008年07月01日
  • 吉本 貴弘, 村井 祐一, 田坂 裕司, 武田 靖 可視化情報学会誌. Suppl. 28 (1) 413 -414 2008年07月01日
  • 神田 哲志, 村井 祐一, 田坂 裕司, 武田 靖, 手塚 英昭, 森 治嗣 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2008 (13) 405 -406 2008年06月18日 
    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.
  • 太田 翔子, 繁富 啓詞, 田坂 裕司, 村井 祐一, 武田 靖, 日夏 宗彦, 児玉 良明 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2008 (13) 227 -228 2008年06月18日 
    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.
  • 村井 祐一 動力・エネルギー技術の最前線講演論文集 : シンポジウム 2008 (13) 163 -164 2008年06月18日 
    Savonius turbine is known as a wind power generator that is driven by drag force acting on two cylindrical blades. The drag is, however, insufficient to maximize the power efficiency because of interaction of fluid around the pair of blades. In order to see and evaluate detailed flow structure, PIV technique is used and applied to Navier-Stokes equations for obtaining pressure field information. With the results, the use of low-pressure region on convex surface of the blade is suggested so that lift force reinforces the torque as drag is lacked. Moreover, streamwise and lateral oscillatory forces around the turbine are discussed in the safety point of view, which need to be investigated to prevent from bending and collapse of the turbine main shaft.
  • Kuroda Ichiro, Sakakibara Akihiko, Sasaki Toshio, MURAI Yuichi, NAGAI Niro, YAMAMOTO Fujio 混相流 22 (2) 161 -174 2008年06月15日
  • 大石 義彦, BREND Mark, THOMAS Peter J., 村井 祐一, 武田 靖 日本流体力学会年会講演論文集 2008 178 -178 2008年 
    Vortex rings translating along the central axis of rigidly rotating fluid are measured by particle tracking velocimetry. The vortex rings with the background rotation break up earlier than these without the rotation. The reason is explained by the momentum exchange promoted between the vortex ring and the surrounding fluid. From the data analysis for translational velocity, vorticity, circulation, and momentum of the vortex ring, we discuss how the spatial development of vortex ring is affected by the rotation.
  • 高橋 潤平, 矢野 可南子, 田坂 裕司, 村井 祐一, 武田 靖, 柳澤 孝寿, 山岸 保子 日本流体力学会年会講演論文集 2008 61 -61 2008年 
    Transition mechanisms of convection cell induced by internal heat sources in a shallow fluid layer are investigated experimentally. We attempt to determine the flow structure in a cell by Particle Image Velocimetry (PIV). Simultaneous multi-layer measurement is performed by color-striped light sheet and transitional state of convection cell is investigated. Vertical velocity component is also obtained and we investigate how cell behaves with respect of R_1 quantitatively. We confirmed cell transition is strongly related with development of descending flow at the center of a cell. Cell dilatation process is described as a consequence descending flow develops and strongly expands at the bottom of the fluid layer.
  • 太田 翔子, 田坂 裕司, 村井 祐一, 武田 靖, 日夏 宗彦, 児玉 良明 海上技術安全研究所報告 8 (2) 224 -224 2008年
  • 吉田 功治, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2007 "102 -1"-"102-4" 2007年11月17日 
    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.
  • 太田 翔子, 田坂 裕司, 村井 祐一, 武田 靖, 日夏 宗彦, 児玉 良明 流体工学部門講演会講演論文集 2007 "911 -1"-"911-4" 2007年11月17日 
    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.
  • 村井 祐一 流体工学部門講演会講演論文集 2007 "WS1 -4-1"-"WS1-4-4" 2007年11月17日 
    A variety of frictional drag reductions achieved by from microbubbles to large film-like bubbles are presented. The most curious fact found from their experiments is that the friction is so sensitively reduced by bubbles when the bubbles are smaller than the fundamental eddies in turbulence. This situation was, in the past, understood to be explained by homogenous model such as by Rheological expression because of less relative velocities between two phases. However the measurement results are unmatched with such a simplified theory. The discussion for the fluid dynamics mechanism is now advancing to extremely complicated model because of inevitable non-homogenous two-phase high-sheared turbulence. Despite to the knowledge accumulated to date, the key process hidden in the drag reduction still must be extracted to utilize the phenomenon as engineering technology that has already begun in maritime innovation. This report mentions how much the original bubbles have such potential to alter the boundary layer as well as the key phenomenon that triggers the effective drag reduction.
  • 竹内 寛貴, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2007 "308 -1"-"308-4" 2007年11月17日 
    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.
  • 矢野 可南子, 田坂 裕司, 村井 祐一, 武田 靖, パトリス ル・ギャル 北海道支部講演会講演概要集 2007 (46) 83 -84 2007年09月29日
  • 田坂 裕司, 村井 祐一, 武田 靖 北海道支部講演会講演概要集 2007 (46) 81 -82 2007年09月29日
  • 高橋 潤平, 矢野 可南子, 田坂 裕司, 村井 祐一, 武田 靖 北海道支部講演会講演概要集 2007 (46) 85 -86 2007年09月29日
  • 藤川 重雄, 村井 祐一 混相流 21 (3) 297 -300 2007年09月15日
  • 田坂 裕司, 矢野 可南子, 村井 祐一, 武田 靖, 柳澤 孝寿 日本流体力学会年会講演論文集 2007 168 -168 2007年 
    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.
  • 野村 勇太, 田坂 裕司, 村井 祐一, 武田 靖 日本流体力学会年会講演論文集 2007 164 -164 2007年 
    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.
  • 児玉 良明, 杉山 和靖, 村井 佑一, Kawamura Takafumi 海上技術安全研究所報告 7 (3) 257 -304 2007年 
    In order to clarify the skin friction reduction mechanism by microbubbles, both experiment and numerical simulation of turbulent channel flow with bubbles were carried out in the same parameter range, and were compared. In the experiment, silicone oil ten times more viscous than water has been used, in order to lower the Reynolds number to that of numerical simulation. The surface tension of the Silicone oil is 1/3 of that of water. In the numerical simulation, two numerical methods have been used. One is the Force Coupling Method (FCM), in which bubbles are assumed to be rigid and the influence of bubbles to the flow is simulated by body forces. The other is the Front-Tracking Method (FTM), in which fluid phase and gas phase are solved simultaneously and bubble shape is allowed to deform by being expressed with polynomials. In the experiment the Reynolds number (Re) is 2,777 to 4,500, and the Weber number (We) is 200. The experimental values of local skin friction shows that the flow is semi-laminar at Re=2,777 in the non-bubble condition, and that, by injecting bubbles, the skin friction increases to the turbulent flow value, which means that bubble injection stimulates the flow and turns it to fully turbulent. At Re=3,734(3,811) the flow is already fully turbulent in the non-bubble condition, and therefore adding bubbles has little influence on the flow, resulting in little change in the skin friction. At even higher Reynolds number of nearly 4,500, adding bubbles decreases skin friction slightly. The Reynolds number of the numerical simulation using FTM is 3,000. The time history of skin friction shows that at the wall where bubbles are clustered by buoyancy local skin friction tends to show slight decrease by adding deformable bubbles (We=100). However, by adding less deformable bubbles (We=50) local skin friction slightly increases. Computation at We=200 has blown up. The local skin friction in the FCM computation at Re=4,000 shows 2.3% increase by adding (rigid) bubbles. Therefore it may be stated that, at Re=3,000, addition of deformable bubbles tends to decrease skin friction, while addition of less deformable bubbles, or rigid bubbles, tends to increase skin friction. In order to carry out numerical simulation of turbulent shear flow with bubbles at higher Reynolds number, the simulation of the homogeneous turbulent shear flow (HTSF) with deformable bubbles has been carried out. The result shows that large turbulent Reynolds number, smaller shear Reynolds number and large Weber number have positive influence on the microbubble drag reduction. The increase of the turbulent Reynolds number of HTFS corresponds to the increase of the Reynolds number of the turbulent channel flow (TCF), and therefore the result agrees with the experimental result that added bubbles decrease skin friction at higher Reynolds number but not at lower Reynolds number. The Weber number dependence of the HTSF result can be compared directly with that of TCF, Thus the result confirms that bubble deformation acts to decrease skin friction.
  • 村井祐一 JSME北海道支部第46回講演会概要集, 2007 79 -80 2007年
  • 近藤 貴幸, 田坂 裕司, 村井 祐一, 武田 靖 熱工学コンファレンス講演論文集 2006 251 -252 2006年11月23日 
    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.
  • 村井 祐一, 田坂 裕司, 太田 翔子, 武田 靖 熱工学コンファレンス講演論文集 2006 249 -250 2006年11月23日 
    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.
  • 今 誓志, 山口 浩平, 大林 寛生, 田崎 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2006 "1708 -1"-"1708-4" 2006年10月28日 
    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.
  • 小嶋 慎哉, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2006 "1705 -1"-"1705-4" 2006年10月28日 
    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.
  • 村井 祐一, 大石 義彦, 武田 靖, Thomas Peter J. 流体工学部門講演会講演論文集 2006 "1702 -1"-"1702-4" 2006年10月28日 
    Vortex ring migrating with background rotation is analyzed experimentally. The rotation field is given by rigid rotation whose axis is parallel to the migrating direction. The transverse velocity and the internal flow structure of the vortex ring are measured by ultrasonic velocity profiler (UVP) with changing the stroke and the velocity of piston-type vortex ring generator. The results show that the transverse velocity decreases with the rotation but keeps its original value when the stroke is long. This trend is explained by the time scale of fluid circulation inside the vortex ring.
  • 小嶋 慎哉, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2006 "1705 -a" 2006年10月28日
  • 今 誓志, 山口 浩平, 大林 寛生, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2006 "1708 -a" 2006年10月28日
  • 村井 祐一, 大石 義彦, 武田 靖, Thomas Peter J. 流体工学部門講演会講演論文集 2006 "1702 -a" 2006年10月28日
  • 大橋 順一, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2006 "1711 -1"-"1711-4" 2006年10月28日 
    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.
  • 大石 義彦, 村井 祐一, LATRACHE Noureddine, 田坂 裕司, 武田 靖 流体工学部門講演会講演論文集 2006 "708 -1"-"708-4" 2006年10月28日 
    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.
  • 田坂 裕司, 小嶋 慎哉, 横山 馨, 村井 祐一, 武田 靖 北海道支部講演会講演概要集 2006 (45) 179 -180 2006年09月25日
  • 竹内 寛貴, 田坂 裕司, 大石 義彦, 村井 祐一, 武田 靖, 手塚 英昭, 森 治嗣 北海道支部講演会講演概要集 2006 (45) 43 -44 2006年09月25日
  • 村井 祐一, 田坂 裕司, 武田 靖 北海道支部講演会講演概要集 2006 (45) 69 -70 2006年09月25日
  • 太田 翔子, 近藤 貴幸, 田坂 裕司, 村井 祐一, 武田 靖 北海道支部講演会講演概要集 2006 (45) 67 -68 2006年09月25日
  • 村井 祐一, 藤井 秀基, 松原 慶明, 大石 義彦, 田坂 裕司, 武田 靖 可視化情報学会誌. Suppl. 26 (1) 315 -316 2006年07月01日
  • 大石 義彦, 森永 聖人, 村井 祐一, 田坂 裕司, 武田 靖, THOMAS Peter J. 可視化情報学会誌. Suppl. 26 (1) 333 -334 2006年07月01日
  • 原 和之, 榊原 昭彦, 村井 祐一, 山本 富士夫 可視化情報学会誌. Suppl. 26 (1) 313 -314 2006年07月01日
  • 田坂 裕司, 柳澤 孝寿, 村井 祐一, 武田 靖 可視化情報学会誌. Suppl. 26 (1) 353 -354 2006年07月01日
  • 榊原 昭彦, 黒田 一郎, 笹木 俊男, 永井 二郎, 村井 祐一, 山本 富士夫 可視化情報学会誌. Suppl. 26 (1) 311 -312 2006年07月01日
  • 森永 聖人, 大石 義彦, 村井 祐一, 田坂 裕司, 武田 靖 可視化情報学会誌. Suppl. 26 (1) 289 -290 2006年07月01日
  • 田坂 裕司, 吉田 将隆, 村井 祐一, 武田 靖, 柳澤 孝寿 日本流体力学会年会講演論文集 2006 177 -177 2006年 
    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.
  • 森永 聖人, 田坂 裕司, 武田 靖, 村井 祐一 日本流体力学会年会講演論文集 2006 128 -128 2006年 
    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.
  • 野村 勇太, 森永 聖人, 田坂 裕司, 村井 祐一, 武田 靖 日本流体力学会年会講演論文集 2006 127 -127 2006年 
    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.
  • 村井 祐一, 田坂 裕司, 武田 靖 流体工学部門講演会講演論文集 2005 155 -155 2005年10月28日
  • 山口 浩平, 今 誓志, 大林 寛生, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2005 161 -161 2005年10月28日
  • 福田 浩士, 大石 義彦, 村井 祐一, 児玉 良明, 山本 富士夫 流体工学部門講演会講演論文集 2005 149 -149 2005年10月28日
  • 大石 義彦, 福田 浩士, 村井 祐一, 児玉 良明, 武田 靖, 山本 富士夫 流体工学部門講演会講演論文集 2005 67 -67 2005年10月28日
  • 大岩 浩司, 村井 祐一, 山本 富士夫 流体工学部門講演会講演論文集 2005 150 -150 2005年10月28日
  • 榊原 昭彦, 黒田 一郎, 笹木 俊男, 永井 二郎, 村井 祐一, 山本 富士夫 流体工学部門講演会講演論文集 2005 151 -151 2005年10月28日
  • 芦原 将彰, 北川 石英, 村井 祐一, 山本 富士夫 流体工学部門講演会講演論文集 2005 72 -72 2005年10月28日
  • 稲葉 一昌, 大橋 順一, 田坂 裕司, 村井 祐一, 武田 靖 流体工学部門講演会講演論文集 2005 65 -65 2005年10月28日
  • 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年10月08日
  • 村井 祐一, 工藤 清, 宮城 直樹 形の科学会誌 = Bulletin of the Society for Science on Form 20 (1) 77 -78 2005年06月01日
  • 北川 石英, 杉山 和靖, 笹木 俊男, 村井 祐一 日本機械学會誌 108 (1038) 348 -348 2005年05月05日
  • 村井 祐一, 藤井 秀基, 西本 匡宏, 田坂 裕司, 武田 靖 可視化情報学会誌. Suppl. 25 (1) 31 -32 2005年03月15日
  • 村井, 中田 大志, 山本 富士夫 日本機械学会流体工学部門講演会講演論文集 (2005-10) 133 -133 2005年
  • 大岩 浩司, 村井 祐一, 山本 富士夫 流体工学部門講演会講演論文集 2004 188 -188 2004年11月24日
  • 村井 祐一, 宮城 直樹, 宮崎 孝司, 山本 富士夫 流体工学部門講演会講演論文集 2004 77 -77 2004年11月24日
  • 太田 淳一, 門谷 光人, 黒瀬 直樹, 村井 祐一, 山本 富士夫 日本機械学會論文集. B編 = Transactions of the Japan Society of Mechanical Engineers. B 70 (693) 1201 -1207 2004年05月25日 
    Efficient techniques for cleaning scale in a U-tube of a heat exchanger are desired. Blast cleaning test was carried out using a real size U-tube of 13.5mm in diameter,8m of straight tube length,and 0.3m in radius of curvature. A combination of plastic particles and glass beads was selected for the blasting media. Swirl motion was added to the blasting media flow. The plastic particle-air two-phase flow with swirl motion in the tube was visualized. The loading ranged from 3.7 to 5.3. The estimated Stokes number was 1700 for the plastic-air two-phase flow. It was observed that just downstream of the bend,flow particle clusters repeatedly each other alternatingly located on the upper and lower sides of the tube. In the repeated blast cleaning experiments,it was found that the same characterstic large-scale cleaning distribution occured along the tube.
  • 大石 義彦, 芦原 将彰, 村井 祐一, 山本 富士夫 講演論文集 2004 (41) 53 -54 2004年03月01日
  • CHENG Wen, MURAI Yuichi, ISHIKAWA Masa-aki, YAMAMOTO Fujio 可視化情報学会論文集合本 = Transactions of the Visualization Society of Japan 23 (11) 107 -114 2004年01月31日
  • 中田, 笹木 俊男, 村井 祐一, 山本 富士夫 日本機械学会流体工学部門講演会講演論文集 (2004-11) 43 -43 2004年
  • 村井 祐一, 長尾 丈太郎, 武田 靖 日本流体力学会年会講演論文集 2004 206 -207 2004年 
    Frictional drag reduction in a horizontal turbulent boundary layer using small bubbles is discussed mathematically and experimentally. Three kinds of turbulent shear stresses are derived from the momentum conservation equation of bubbly flow, i.e., Reynolds shear stress, vertical correlation stress, and triple correlation stress. The experimental data indicate that the triple correlation term among them has an important role to reduce the total frictional drag while Reynolds stress profile has its peak at a far distance from the wall in the case of mixing bubbles. Also, the mean relative velocity between bubbles and liquid in the turbulent boundary layer is derived to estimate the experimental data.
  • 清水 学, 大岩 浩司, 村井 祐一, 山本 富士夫 計算力学講演会講演論文集 2003 (16) 109 -110 2003年11月22日 
    The effective viscosity of bubbly liquid is governed not only by void fraction but also by bubble's deformation whose effect is expressed with Capillary number. In this study, two kinds of bubbly two-phase flow are analyzed with using the model of the effective viscosity to confirm the effect of bubble's deformation on the time-averaged velocity profiles in laminar flow conditions.
  • 村井 祐一, 大岩 浩司, 山本 富士夫 流体工学部門講演会講演論文集 2003 187 -187 2003年09月18日
  • 大石 義彦, 村井 祐一, 石川 正明, 山本 富士夫 流体工学部門講演会講演論文集 2003 156 -156 2003年09月18日
  • 中島 羊一, 村井 祐一, 井戸 健敬, 山本 富士夫 流体工学部門講演会講演論文集 2003 86 -86 2003年09月18日
  • 芦原 将彰, 北川 石英, 村井 祐一, 山本 富士夫 流体工学部門講演会講演論文集 2003 20 -20 2003年09月18日
  • 笹木 俊男, 村井 祐一, 山本 富士夫 混相流 17 (3) 296 -304 2003年09月15日
  • 上埜 安隆, 村井 祐一, 山本 富士夫 可視化情報学会誌. Suppl. 23 (1) 57 -58 2003年07月01日
  • 石川 正明, 村井 祐一, 酒井 康丞, 戸田 信一, 吉川 信治, 山本 富士夫 可視化情報学会誌. Suppl. 23 (1) 373 -376 2003年07月01日
  • 中島 羊一, 井戸 健敬, 石川 正明, 村井 祐一, 山本 富士夫 講演論文集 2003 (40) 85 -86 2003年03月01日
  • 笹木 俊男, 永井 二郎, 村井 祐一, 山本 富士夫 講演論文集 2003 (40) 91 -92 2003年03月01日
  • ISHIKAWA Masaaki, MURAI Yuichi, SAKAI Kosuke, YAMAMOTO Fujio, TODA Shinichi, TAMAYAMA Kiyoshi Proceedings of the ... International Conference on Nuclear Engineering. Book of abstracts : ICONE 2003 283 -283 2003年
  • 北川 石英, 芦原 将彰, 村井 祐一, 山本 富士夫 海上技術安全研究所報告 3 (2) 224 -224 2003年
  • 大岩 浩司, 村井 祐一, 高橋 義明, 山本 富士夫 混相流 = Japanese journal of multiphase flow 16 (4) 372 -379 2002年12月15日
  • 石川 正明, 村井 祐一, 漁野 嘉昭, 酒井 康丞, 戸田 信一, 玉山 清志, 山本 富士夫 可視化情報学会誌 = Journal of the Visualization Society of Japan 22 289 -292 2002年07月01日
  • 井戸 健敬, 下岡 久晴, 清水 寛正, 石川 正明, 村井 祐一, 山本 富士夫, 増田 頼保 可視化情報学会誌 = Journal of the Visualization Society of Japan 22 385 -388 2002年07月01日
  • 村井 祐一 混相流 = Japanese journal of multiphase flow 16 (1) 44 -47 2002年03月15日
  • 松原 朋昭, 石川 正明, 村井 祐一, 山本 富士夫 講演論文集 2002 (39) 99 -100 2002年03月08日 
    Combined technique of Particle Imaging Velocimetry (PIV) in conjunction with Computational Fluid Dynamics (CFD) makes it possible to predict detailed fluid flow structures. Turbulent flow containing fine solid particles in a channel is one of typical examples which are not solved only by PIV nor by CFD. In this study, the solid particle behavior in a converging channel is predicted by theoretical equations after the carrier phase flow field is measured by PIV. The results have shown the dependency of the particle behavior on its force components, such as inertia and lift forces.
  • 太田 淳一, 杉本 剛敏, 村井 祐一, 關 雅彦, 黒田 雄二, 山本 富士夫 流体工学部門講演会講演論文集 2001 105 -105 2001年09月28日
  • 足利 昌俊, 荻野 ゆりか, 高橋 麻美, 湊 茂治, 安藤 公一, 工藤 清, 清水 寛正, 松原 朋昭, 村井 祐一 可視化情報学会誌 = Journal of the Visualization Society of Japan 21 71 -72 2001年09月01日
  • 清水 寛正, 井戸 健敬, 村井 祐一, 山本 富士夫 可視化情報学会誌 = Journal of the Visualization Society of Japan 21 51 -54 2001年09月01日
  • 石川 正明, 井戸 健敬, 北川 石英, 松原 朋昭, 村井 祐一, 山本 富士夫 可視化情報学会誌 = Journal of the Visualization Society of Japan 21 129 -132 2001年07月01日
  • 藤元 宏一, 村井 祐一, 南 友和, 山本 富士夫 日本機械学会論文集. B編 67 (658) 1400 -1407 2001年06月25日 
    This paper concerns with flow visualization and image measurement of bubbly flows around several shapes of obstacle. Coaxially confined twin rectangular tanks are constructed in order to provide a wide two-dimensional uniform bubble distribution upstearm of the obstacle. The experiments show that a quite large two-phase convection is induced by inserting the obstacle into the bubbly flow. Spatial scale of the two-phase convection depends on the shape of the obstacle as well as its arrangement. Measurement results of void fraction, bubble velocity and liquid phase flow, which are obtained by PIV and PTV, explores the detailed mechanism of generating the convection. Especially, the interaction between accumulated bubbles in upstream the object and downward liquid flow behind the object determines the scale of the two-phase convection.
  • 大岩 浩司, 村井 祐一, 山本 富士夫 計算工学講演会論文集 6 (1) 261 -264 2001年05月30日
  • 村井 祐一, 大野 泰, ハッサン アブダルムテイ, 山本 富士夫 日本機械学会論文集. B編 67 (657) 1120 -1127 2001年05月25日 
    Flow in the vicinity of free surface induced by a bubble plume is utilized as one of effective ways to control the surface floating substances on lakes, oceans, as well as in various kinds of reactors handling a free surface. In this work, a two-dimensional flow analysis based on Eulerian-Lagrangian model and particle tracking velocimetry measurement have been carried out in order to elucidate the surface flow generation process in detail. The present results explore the following points : 1) Surface velocity profile can be predicted by the Eulerian-Lagrangian model with a good agreement with experimental results, 2) maximum velocity of the surface flow increases as large void fraction with small bubble size is supplied, 3) The surface flow is effectively generated in case of bubble plume compared to liquid jet flow because distortion point appears in the vicinity of surface.
  • 山本 富士夫, 村井 祐一 可視化情報学会誌 = Journal of the Visualization Society of Japan 21 (80) 2 -7 2001年01月01日
  • FUJIMOTO K., ISHIKAWA M., MINAMI T., MURAI Y., YAMAMOTO F. Journal of visualization 4 (3) 213 -213 2001年
  • 井戸 健敬, 村井 祐一, 山本 富士夫 日本機械学会論文集. B編 66 (649) 2257 -2264 2000年09月25日 
    Accurate post-processing methods are required in order to analyze the detailed flow structures from the data of particle tracking velocimetry. In particular, both spatial distributions of vorticity and stream functions cannot be obtained reasonably in the case of sparse data resulting from popular conventional methods. This paper proposes a new post-processing algorithm based on ellipsoidal differential equations which enable to utilize boundary condition data efficiently. The performance of the algorithm is examined by applying them to two-dimensional vortex flows and isotropic turbulent flows. The results reveal that the present algorithm has the highest accuracy in comparison with several popular methods for detecting vorticity, energy, and the energy spectrum.
  • 大岩 浩司, 大野 泰, 村井 祐一, 山本 富士夫 流体工学部門講演会講演論文集 2000 134 -134 2000年09月08日
  • 井戸 健敬, 村井 祐一, 山本 富士夫 可視化情報学会誌 20 (1) 241 -244 2000年07月
  • 村井 祐一, 北川 石英 混相流 = Japanese journal of multiphase flow 14 (1) 115 -116 2000年03月15日
  • 井戸 健敬, 村井 祐一, 山本 富士夫 日本機械学会関東支部総会講演会講演論文集 2000 (6) 181 -182 2000年03月10日 
    The Visualization Society of Japan provides PIV-standard images for evaluating PIV and PTV algorithms. By using the PIV-standard images, post-processing methods of PTV have been evaluated by reconstructing the vorticity with or without errors in PTV data. As a result, one of the post-processing methods, named "Biquadratic-ellipsoidal Equation Rearrangement" method, has a good performance in case of no error, but the method is liable to be influenced by the errors.
  • 久田松 潤, 村井 祐一, 陳 剛, 山本 富士夫 講演論文集 2000 (37) 213 -214 2000年03月01日
  • 大岩 浩司, 大野 泰, 村井 祐一, 山本 富士夫 講演論文集 2000 (37) 215 -216 2000年03月01日
  • ASHIHARA Masa-aki, MURAI Yuichi, BAE Dae Seok, YAMAMOTO Fujio Proceedings of the ... JSME-KSME Thermal Engineering Conference 1 "1 -319"-"1-324" 2000年 
    Bubble motion near a vertical flat wall in a quiescent liquid has been investigated by using particle tracking velocimetry (PTV). The bubbles showed a variety of behavior, such as sliding, flapping, and jumping on the wall. The present study was focused on the sliding behavior to clarify the transition mechanism of bubble's arrangement pattern from homogeneous arrangement to heterogeneous arrangement in the case of high void fraction. From the statistical values of the experimental results, bubble-bubble interaction structure in wall-sliding bubbles was made clear.
  • 石川 正明, 井戸 健敬, 村井 祐一, 山本 富士夫 日本流体力学会年会講演論文集 2000 253 -254 2000年 
    We have proposed a rearrangement maethod based on Laplace cquation for velocity. It is difficult to obtain first order differential values correctly such as the velocity gradient tensor, because the equation deals with the multi-dimensional linear transformation. There ore, we furthermore adapted Laplace equations for velocity gradient tensor, it was posible to correctly calculate velocities and velocity gradient tensors. This rearrangement method is applied to homogeneous turblent flow, the performance of this method is examined in comparison with the inverse distance rearrangement method.
  • 篠田 圭司, 太田 淳一, 村井 祐一, 山本 富士夫 インテリジェント・システム・シンポジウム講演論文集 = FAN Symposium : fuzzy, artificial intelligence, neural networks and computational intelligence 9 546 -549 1999年10月
  • 石川 正明, 村井 祐一, 太田 淳一, 山本 富士夫 年会一般講演 18 63 -64 1999年07月29日
  • 村井 祐一, 宋 向群, 高木 崇, 石川 正明, 山本 富士夫, 太田 淳一 日本機械学会論文集. B編 65 (632) 1339 -1346 1999年04月25日 
    The inverse energy cascade,which is one of the important phenomen α to enhance the large scale flow instability in bubbly flow,is investigated by measuring a local two phase flow structure driven by buoyant bubbles using Particle Imaging Velocimetry (PIV). In the PIV,flow field of liquid phase is measured by separating an original image to respective two phase images using a statistical thresholding method for image parameters of bubble and particle. The present results obtained in case that bubble Reynolds number and average void fraction are less than 30 and 1.5% respectively,confilm the presence of a large energy-decaying with slope index of sharper than -5/3 in log-log diagram of energy spectrum at high wavenumber region. Also an important relationship between the energy spectrum and bubble-bubble interval distance is detected.
  • 村井 祐一, 北川 石英, 宋 向群, 山本 富士夫, 太田 淳一 日本機械学会論文集. B編 65 (632) 1347 -1354 1999年04月25日 
    The inverse energy cascade in bubbly flow is investigated by a numerical simulation using the Eulerian-Lagrangian model in which the governing equations are formulated with emphasis on the translational motion of bubbles in non-uniform flow. This paper is concerned with the validation of the numerical model and various parametric dependency on the inverse cascade. The calculated results reveal that, 1)continuous growth of the spatial fluctuation scale in a bubble-induced flow is well predicted by the present numerical model and the results have a good analogy with the experimental results which are introduced in our first report, 2)the strong relationship between energy decaying process and bubble-bubble distance interval identified also by the present analysis, 3)the slope of energy-decaying at high wavenumber region depends on the kinetic viscosity of liquid,and that at low wave number region depends on inunifornity of buoyancy distribution which changes due to the bubble motion.
  • 村井 祐一, 渡部 正夫, 細川 茂雄, 藤川 重雄 混相流 = Japanese journal of multiphase flow 13 (1) 61 -62 1999年03月15日
  • 太田 淳一, 村井 祐一, 山本 富士夫 福井大学地域共同研究センタ-年報 7 86 -89 1999年
  • 村井 祐一, 松本 洋一郎, 宋 向群, 山本 富士夫 日本機械学会論文集. B編 64 (626) 3257 -3263 1998年10月25日 
    Turbulence structure in rising bubbly flow driven by bubble buoyancy was analyzed by using the Eulerian-Lagrangian equation model. A new calculation method for two-way interaction between dispersed bubble and liquid phase was proposed to simulate accurately the local fluctuation of liquid flow induced by bubble migration. The present two-dimensional simulation revealed that, (1) the turbulence structure had the longer wave length in vertical direction in case of the larger bubble, (2) the wave spectrum of kinetic energy of the liquid phase depended sensitively on the average void fraction and the lift force of bubble.
  • 村井 祐一, 井戸 健敬, 石川 正明, 山本 富士夫 日本機械学会論文集. B編 64 (626) 3249 -3256 1998年10月25日 
    Since velocity vectors obtained by Particle Imaging Velocimetry are distributed discretely depending on the number density of tracer particles seeded in the objective flow, a new estimation algorithm to reconstruct the whole-field flow has been proposed using the Laplace equation for velocity vector and the Poisson equation for velocity correction potential. Performance of the algorithm was examined with two-dimensional vortex flow, and the validity was evaluated quantitatively by two-dimensional correlation coefficient. The present algorithm was applied to torque converter internal flow, and the results reveal that the present method is applicable for various conditions to analyze the whole-field flow structure.
  • 井戸 健敬, 村井 祐一, 山本 富士夫 可視化情報学会誌 = Journal of the Visualization Society of Japan 18 71 -74 1998年07月01日
  • 村井 祐一, 松本 洋一郎 日本機械学会論文集. B編 63 (611) 2283 -2288 1997年07月25日 
    A numerical analysis using the Lagrangian tracking method for bubbly flow was carried out to elucidate the three-dimensional detailed flow structure and the turbulence mechanism of a bubble plume, which has various interaction between gas and liquid phases. The results revealed that the bubble plume exhibits several kinds of three-dimensional structures with spiral and sinuous behaviors, depending on bubble size and void fraction. This macroscopic structure shows good agreement with experimental observation. Also, the bubble plume has a turbulence component, called pseudo turbulence with high frequency which is caused by the migration of large bubbles with large slip velocity inside the bubble plume.
  • 村井 祐一, 松本 洋一郎 日本機械学会論文集. B編 63 (611) 2277 -2282 1997年07月25日 
    Detailed flow structure of bubbly flows observed in a bubble plume is investigated by numerical simulation using the Lagrangian tracking method which can treat the bubble movement with high accuracy. Governing equations are formulated with emphasis on the translational motion of bubble in non uniform unsteady liquid flow. Numerical results reveal the dependency of bubble size distribution on the flow behavior and show good agreements with experimental results. In this 1st report, two-dimensional bubble plumes are chosen for analysis of detailed flow structure in bubbly flow.
  • Hassan Abdul-Mouti, 山本 富士夫, 村井 祐一, 小林 康宏 可視化情報学会誌 = Journal of the Visualization Society of Japan 17 239 -242 1997年07月01日
  • 山本 富士夫, 和田 存功, 宋 向群, 村井 祐一, 石川 正明, 井口 学 可視化情報学会誌 = Journal of the Visualization Society of Japan 17 129 -132 1997年07月01日
  • 石川 正明, 山本 富士夫, 井口 学, 村井 祐一, 和田 存功 可視化情報学会誌 = Journal of the Visualization Society of Japan 16 23 -26 1996年11月01日
  • 村井 祐一, 高木 周 混相流 10 (3) 327 -328 1996年09月15日
  • 村井 祐一, 松本 洋一郎 日本機械学会論文集. B編 62 (593) 85 -92 1996年01月25日 
    Bubbly flows exhibit various structures, such an incompressible or compressible behavior depending on the void fraction. In the present study, a new numerical method is developed for bubbly flows in order to treat the compressibility stably and effectively, by derivation of the pressure equation from the governing equations based on the two-fluid model. By simulations of several different bubbly flows including a transonic flow, it has been shown that the present method is applicable to wide range bubbly flows in compressibility, and also that calculation efficiency and stability are better than the other solver.
  • 松本 洋一郎, 村井 祐一 日本機械学会論文集. B編 61 (588) 2818 -2825 1995年08月25日 
    A bubble-driven plume in a tank with a free surface is investigated numerically using the bubble flow model equations which are formulated with emphasis on the relative transverse motion and volumetric change of the bubble. A numerical scheme is developed by the derivation of the pressure equation for the bubbly flow in order to treat the effects of the relative motion between two phases and the compressibility of the bubble accurately. From the numerical results, the three-dimensional flow structure of the bubble-driven plume has been shown in detail, where there are turbulences on various scales caused by the interaction of liquid convection and bubble motion.

書籍等出版物

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

講演・口頭発表等

  • Ship frictional drag reduction using hydrofoil bubble generators  [通常講演]
    Y.Murai, I.Kumagai
    11th International Conference on Multiphase Flow (ICMF 2023) 2023年04月 口頭発表（一般）
  • Color contamination matrix property assessment for improvement of colored smoke PIV  [通常講演]
    Y.Murai, Y.Horimoto, H.J.Park, Y.Tasaka
    14th International Symposium on Particle Image Velocimetry- Chiago, USA 2022年08月 口頭発表（一般）
  • UVP applied for Doppler scanning of fruit-internal structures and its working principle  [通常講演]
    Y.Murai, T.Yoshida, H.J.Park, Y.Tasaka
    13th International Symposium on Ultrasound Doppler Method 2021 - Zurich 2022年06月 口頭発表（一般）
  • Frictional drag reduction by controlling of bubble injection  [招待講演]
    Y.Murai
    AQUA meeting - Keynote No.1 (2022) 2022年05月 口頭発表（基調）
  • Current multiphase flow research activities in Japan and the U.S.  [招待講演]
    Y.Murai, G.Tryggvason
    U.S.-Japan Seminar on Two-Phase Flow Dynamcs 2022 - Michigan 2022年05月 口頭発表（招待・特別）
  • Slug-jamming of gas-liquid two-phase flows in a helically coiled tube  [通常講演]
    Y.Murai, M.Ishikawa
    U.S.-Japan Seminar on Two-Phase Flow Dynamcis 2022 - Michigan 2022年05月 口頭発表（一般）
  • Savonius wind turbine performance in high turbulence and its improvement by jet supply  [通常講演]
    Y.Murai, T.Umemura, R.Sayama, Y.Horimoto, H.J.Park, Y.Tasaka, S.Otomo
    International Conference on Power Engineering 2021 -Kobe 2021年10月 口頭発表（一般）
  • Keynote: Advances in color particle image velocimetry and color particle tracking velocimetry using color coded volumetric illumination  [招待講演]
    Y.Murai
    19th International Symposium on Flow Visualization, Shanghai, China (2021, 9/14-16) 2021年09月 口頭発表（招待・特別）
  • Keynote: Ultrasonic Doppler measurement of multiphase flows  [招待講演]
    Y.Murai
    Int. Multiphase Flow Technology Forum 2020年01月 シンポジウム・ワークショップパネル（指名）
  • Plenary: Velocity profiling rheometry for dispersed multiphase fluids[Plenary Lecture]  [招待講演]
    Y.Murai
    10th International Symposium on Measurement Techniques for Multiphase Flow - Hong Kong 2017年12月 口頭発表（基調）
  • 混相流の流量計測技術  [招待講演]
    村井祐一
    産総研 流量計測WG招待講演会 2017年10月 口頭発表（招待・特別）
  • 改心 科研申請  [招待講演]
    村井祐一
    旭川高専 特別講演会 2017年09月 公開講演，セミナー，チュートリアル，講習，講義等
  • 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  [招待講演]
    村井祐一, 熊谷一郎, 田坂裕司, 朴 炫珍, 高橋義明
    国立科学博物館出展（日本機械学会賞受賞出展） 2017年07月 メディア報道等
  • Two-phase flow research activities in Japan, U.S., and E.U.  [招待講演]
    Y.Murai, G.Tryggvason, Y.Takeda
    11th Japan-U.S. Seminar on Two-Phase Flow Dynamics 2017年06月 シンポジウム・ワークショップパネル（指名）
  • Laboratory experiments and sea-trials on ship drag reduction by bubble injection [keynote]  [招待講演]
    Y.Murai
    9th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics (ExHFT-9) 2017年06月 口頭発表（招待・特別）
  • Advance of particle tracking velocimetry toward ultimate use in multidisciplinary fields  [招待講演]
    Y.Murai
    Special Lecture at Swiss Federal Institute of Technology (ETHZ) 2017年03月 口頭発表（招待・特別）
  • 液状食品の超音波非接触モニタリング技術  [招待講演]
    村井祐一, 芳田泰基, 朴炫珍, 田坂裕司
    日本食品科学工学会北海道支部大会 2017年02月 口頭発表（招待・特別）
  • 機械工学をベースとした環境エネルギー技術の開発  [招待講演]
    村井祐一
    都城高専 機械工学科特別講演会 2016年12月 公開講演，セミナー，チュートリアル，講習，講義等
  • Bird shadow imaging coupled with wire-frame model analysis for automatic bird species identification  [招待講演]
    Y.Murai, Y.Takeda, H.Kumeno
    2nd Meeting of Workgroup of Birdstrike Science and Engineering 2016年10月 口頭発表（招待・特別）
  • Multi-polar vortex dynamics of dispersion-induced flow control  [招待講演]
    Y.Murai, c, ur
    China Sympoisum on Multiphase Flow Measurement 2016年09月 口頭発表（基調）
  • 世界と共同開発、流体力学から湧き出るアイデアの実用化  [招待講演]
    村井祐一
    北海道青少年科学文化財団公開講座 2016年03月 公開講演，セミナー，チュートリアル，講習，講義等
  • Frictional drag reduction by small bubbles versus large bubbles  [招待講演]
    Y.Murai, Y.Tasaka, H.Park
    Workshop on Transition Control in Dispersed Flows 2016年01月 口頭発表（招待・特別）
  • Measurement-based discovery on new function of microbubbles in fluid flow  [招待講演]
    Y.Murai
    Internatioal Forum on New Horizons in Multiphase Flow Measurement 2015年12月 口頭発表（招待・特別）
  • マイクロバブルの最前線  [招待講演]
    村井祐一
    函館高専 先端科学技術講演会 2015年12月 公開講演，セミナー，チュートリアル，講習，講義等
  • 科学するこころ  [招待講演]
    村井祐一
    石川高専オープンカレッジ講演会 2015年11月 公開講演，セミナー，チュートリアル，講習，講義等
  • 夢を追いかけてー自然・人との調和をめざす未来の研究ー  [招待講演]
    村井祐一
    石川高専創立50周年記念事業記念講演会 2015年11月 公開講演，セミナー，チュートリアル，講習，講義等
  • 超音波ドップラーレオメトリーの開発  [招待講演]
    村井祐一
    化学工学会第47回秋季大会 2015年09月 口頭発表（招待・特別）
  • Microbubble-liquid interaction observed in channel flows from laminar, transition, and turbulent regimes  [招待講演]
    Y.Murai, Y.Tasaka, Y.Oishi (keyno
    ASME International Conference on Nano, Micro, and Minichannels 2013年 口頭発表（基調）
  • Fundamentals in frictional drag reduction by bubble injection  [招待講演]
    Y.Murai (k
    International Conference on Multiphase Flow 2013 2013年 口頭発表（基調）
  • Paradigm shift in modern flow measurement and gas flow metering  [招待講演]
    Y.Takeda, Y.Murai (k
    International Gas Research Conference - Korea 2012年 口頭発表（招待・特別）
  • Broad destruction of density stratification using a single bubble plume  [招待講演]
    Y.Murai, H.Kayukawa, Y.Tasaka, I.Kumagai, H.Kitaura
    Japan-US Seminar on Two-Phase Flow Dynamics - Tokyo 2012年 口頭発表（基調）
  • Particle Tracking AccelerometryによるPIVの粒子追従性問題からの解放  [招待講演]
    村井 祐一
    JAXA第4回EFD/CFD融合ワークショップ 2011年 口頭発表（招待・特別）
  • マイクロバブルが乱流渦の成長を選択的に鎮圧する現象について  [招待講演]
    村井 祐一
    日本混相流学会年会講演会2011京都 2011年 口頭発表（基調）
  • 単視点型カラートモグラフィック３次元ヴォクセルPIV  [招待講演]
    村井祐一, 田坂裕司, 武田 靖, 神田哲志(keyno
    第87期日本機械学会流体工学部門講演会 2009年 口頭発表（基調）
  • 超音波パルスによる二相流動場の高精細計測 ～ 光計測に優る点  [招待講演]
    村井 祐一(k
    第12回オーガナイズド混相流フォーラム 2008年 口頭発表（招待・特別）
  • Backlight imaging tomography applied to slug flows in straight and helical tubes  [招待講演]
    Y.Murai, Y.Takeda, F.Yamamoto
    5th Int. Symposium on Measurement Techniques for Multiphase Flows 2006年 口頭発表（基調）
  • 再帰型相互相関PIVによるエアレーション流動場の高精細計測  [招待講演]
    村井祐一, 程 文, 笹木俊男, 山本富士夫
    日本混相流学会年会講演会2005 2005年 口頭発表（基調）
  • Turbulent Shear Stress Profiles in a Horizontal Bubbly Channel Flow  [通常講演]
    Y.Murai, Y.Oishi, T.Sasaki, Y.Kodama, F.Yamamoto
    6th International Symposium on Smart Control of Turbulence 2005年 口頭発表（招待・特別）
  • Experimental Study on Bubble Behavior Contributing to Frictional Drag Reduction  [招待講演]
    Y.Murai, H.Oiwa, Y.Ooishi, F.Yamamoto
    U.S.- Japan Workshop on Microbubble Friction Drag Reduction 2003年 口頭発表（基調）
  • Application of Particle Tracking Velocimetry to Multiphase Flows - New Finding with It  [通常講演]
    Y.Murai, F.Yamamoto
    Int. Symp. Optical Methods and Image Processing in Fluid Flow Measurement,ASME/FED & JSME Joint Fluids Conferenc 2003年 口頭発表（基調）
  • 気泡流の微細流動構造,その CFD と EFD [基調講演]  [招待講演]
    村井 祐一
    日本機械学会第76期流体工学部門講演会 1998年 口頭発表（基調）
  • 気泡流の CFD 予測と PIV 計測 [招待講演]  [招待講演]
    村井 祐一
    第１回オーガナイズド混相流フォーラム 1997年 口頭発表（招待・特別）

担当経験のある科目（授業）

  • 情報学 （北海道大学 教養部)Informatics
  • 線形代数福井大学
  • 日本文化（工業）福井大学
  • 機械の世界福井大学
  • 機械工学実験福井大学
  • 機械英語福井大学
  • 流体工学北海道大学
  • 物理工学コロキウム北海道大学
  • 熱流体力学演習北海道大学
  • 地球原子力物理と倫理北海道大学
  • 計測工学実験北海道大学
  • 機械知能工学入門北海道大学
  • 情報センシング工学福井大学
  • 環境エネルギー工学北海道大学
  • 地球環境とエネルギー北海道大学
  • ラボラトリーセミナー北海道大学
  • データ解析学北海道大学
  • Advanced Fluid Engineering (in English)北海道大学
  • エネルギー工学概論北海道大学
  • テクニカルイングリッシュ北海道大学
  • 応用数学北海道大学
  • 流体エネルギー変換工学北海道大学
  • エネルギー機械福井大学
  • 画像情報科学特論福井大学
  • 流体情報科学特論北海道大学、福井大学
  • 流体力学北海道大学
  • 流体システム工学（集中講義）金沢大学
  • 工学創成実験（風力発電）北海道大学
  • Energy Policy and Technology (in English)北海道大学
  • Nuclear and Various Energy Systems (in English)北海道大学
  • Fluid Power Systems (in English)北海道大学

所属学協会

  • アメリカ物理学会   日本機械学会   可視化情報学会   日本流体力学会   日本混相流学会   英国物理学会   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2023年04月 -2027年03月 
    代表者 : 田坂 裕司, PARK HYUNJIN, 柳澤 孝寿, 堀本 康文, 村井 祐一
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2021年04月 -2026年03月 
    代表者 : 村井 祐一, 田坂 裕司, PARK HYUNJIN, 熊谷 一郎, 堀本 康文, 北川 石英, 大石 義彦
     
    令和３年度は，以下の研究調査を進めた．一次元ボイド波伝播モデルによるPBIの適用距離の予測(朴)，３次元翼による微細気泡発生法と正味摩擦抵抗低減効果の検討（熊谷）， 高時間分解レーザーせん断応力計の開発とVITA法適用による統計評価（大石），空気充填ディンプルに形成される気膜の計測とマイクロ気膜法に関する予備調査（北川），非定常剪断流れにおける分散混相流体の実効粘度（田坂），高Reynolds数Taylor-Couette乱流の速度計測と抵抗低減（堀本），水平チャネルにおいて大型気泡群を有する2相乱流流動の直接数値シミュレーション（村井），傾斜チャンネル内の境界層で挙動する気泡抗力係数算定（村井）．間欠的気泡注入による抵抗低減効果の長距離持続化（朴），水平チャネルのボイド率急変時の乱流境界層構造のステップ応答の計測（村井）． これらの成果は抵抗低減における気泡運動の流体力学について IJMFに4偏，気泡を含む応力場の計測技術について Exp Fluidsに4偏，船舶抵抗低減の実スケール実験について Ocean Engに2編，気泡流の非線形流体力学について JFMに1編，その他を含めて計18編の学術雑誌に掲載された．本課題で主柱としている下記の3項目について，初年度としての進展のうち特筆すべきものに以下が挙げられる．[PBI] 気泡分布の時空間パターン制御について，船底ボイド波のKdV-Burgers方程式によるデータ解析から現象相似性が発見された．[HBC] 水中翼による局所減圧型の境界層気泡分布制御法の開発では，微細気泡分散状態とエアキャビティ状態のモード変換機構が解明された．[RMF] 超音波と光による実時間フィードバック制御の開発では，複雑せん断流体の実効粘度の周波数依存性を計測する技術が確立された．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2022年04月 -2025年03月 
    代表者 : 北川 石英, 高木 知弘, 外岡 大志, 村井 祐一, 渡村 友昭
     
    抵抗低減・伝熱促進・反応促進技術では，壁面近傍での分散体のサイズ・挙動・分布構造が機器性能に直接的影響を与える．本研究では，濡れ性操作によって表面の機能化を図り，分散体挙動・分布構造を自在に制御することを目的として，スケールの異なる４つの流れ場，流場①「マイクロチャネル流れ」，流場②「界面衝突流れ」，流場③「水平チャネル流れ」，流場④「テイラークエット流れ」を対象とした調査を実施した．その結果，流場①では，親水性・疎水性部分をマイクロパターニングしたガラス基板上で微小な水滴がアレイ状に形成されることを確認した．流場②では，実験に対して，固定された物体後流の遷移が過去の文献で示された結果と定性的に一致することを確認し，数値計算に対して，複数の相を取り使うことが可能な multiphase-field 法を構築した．流場③では，機能表面を利用した移流気泡群の一方向輸送実験を行い，撥水面を二分割することにより，高レイノルズ条件下での気泡輸送率の向上に成功した．最後に，流場④では，テイラークエット流れ場に気体を注入した場合の移流・拡散プロセスの計測を行い，高速移流気泡群と集積定在気泡群の2つが共存する気液二相流を実現した．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2022年04月 -2025年03月 
    代表者 : 北川 石英, 高木 知弘, 外岡 大志, 渡村 友昭, 村井 祐一
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2021年04月 -2025年03月 
    代表者 : 正信 聡太郎, 村井 祐一, 高野 慧, 山本 マルシオ
     
    海洋鉱物資源開発においては揚鉱ユニットが技術的な中核を担う。揚鉱ユニットの設計及び運用においては、揚鉱管・移送管内のフローアシュアランス（流路保全）分析が必須であるが、管の傾斜や動揺等を考慮した非定常の固液二相流に対するリアルタイム分析技術がないため一連の技術開発を遅延させている。そこで本研究では、超音波計測技術を独自開発し、管内を脈動する固液二相流の流動状況と圧力損失の周波数スペクトル空間での因果関係を解明してフローアシュアランス分析に適用可能な圧力損失推定手法を構築する。さらに、圧力損失を低減可能な制御デバイスを開発するとともに、内部流との相互作用が分析できる水中線状構造物の応答予測手法を構築する。 当該年度は、以下の課題を実施した。 【①圧力損失推定技術の開発】 鉛直管を対象とした脈動流中における時間領域圧力損失推定プログラムの基本アルゴリズムを検討するとともに、過去に構築した定常状態での圧力損失推定手法を用いて、移送管の形状変化が圧力損失に及ぼす影響を調査して、試設計した移送管に対する最適な移送条件（固相体積濃度、平均流速）を設定した。2022年度に実施を計画している、口径25Aの円管を鉛直から水平まで傾斜可能な固液二相流の移送実験計画を策定するとともに、当該実験装置を製作した。さらに、2022年度に検討予定であった口径80Aの円管を用いた移送実験計画も前倒して策定した。また、管内を流動する粗大粒子を位置特定して計数する超音波エコーグラフィの計測技術について基本信号処理アルゴリズムを開発した。 【②圧力損失最小化技術の開発】 超音波スピニングレオメトリー(USR)により固体粒子懸濁液のレオロジーの計測を実施した。 【③水中線状構造物の応答予測手法の開発】 内部流を考慮しない水中線状構造物挙動の応答予測プログラムを開発した。
  • 超音波を用いた混相流の計測技術の開発
    石油天然ガス・金属鉱物資源機構［JOGMEC］：
    研究期間 : 2020年04月 -2023年03月
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2019年04月 -2023年03月 
    代表者 : 田坂 裕司, PARK HYUNJIN, 村井 祐一
     
    ①混相流体の局所非定常レオロジー物性の評価，②実効乱流渦粘度の評価，③気泡集積と渦の安定性評価，④局所乱流塊と気泡の干渉，を個別プロジェクトとして設定し研究を進めた． ①に関して，これまでに構築した超音波スピニングレオメトリ（USR）を用いて，非ニュートン流体に粒子が混入した場合の実効粘度および実効弾性の変調を評価し，理論的な考察を加えた．これらの結果は論文にまとめられ掲載された．またUSRを拡張し，のこぎり波など自由な加振モードに対応するため，のこぎり波がフーリエ変換によりいくつかの周波数成分に展開されることから，複数の周波数成分を持つ振動を加えた場合の方法論を構築した． ②に関して，レイノルズ方程式を基準の運動方程式として用いることで，実効渦粘度を評価するアルゴリズムを構築した．また，これを用いた評価を行うための計測装置として，小型のテイラー・クエット流れとそこにマイクルバブルを含む水を導入するための装置考案した． ③移流しながらの渦による気泡の集積挙動とその渦への影響を調べるため，ラインスキャンカメラを用いた新たな計測法を開発し，気泡チャネル流の装置を用いてその性能を検証した． ④円管内に生じる局所乱流塊である，乱流パフの形成・減衰挙動を，乱流塊とともに移動するカメラによるラグランジュ計測により捉えた．可視化結果から形成過程に現れる特徴的な振る舞いを抽出し，次年度に定量化実験を行うためのパラメータ領域を明瞭にした．また，管壁に設置した出っ張りが乱流塊に及ぼす影響を調査し，条件によっては流れを乱すのではなく，乱流塊を減衰させ，流れを再層流化に導くことを示した．
  • 超音波による表面温度計測技術の開発
    三菱重工業株式会社：
    研究期間 : 2020年08月 -2022年03月
  • 導管設備を用いたマイクロ風力発電の効率化に関する研究
    東京ガス株式会社：
    研究期間 : 2020年07月 -2022年03月 
    代表者 : 村井祐一,朴炫珍,堀本康文,田坂裕司
  • 日本学術振興会：科研費：国際共同研究強化B
    研究期間 : 2018年10月 -2022年03月 
    代表者 : 村井 祐一
  • 乳製品製造工程中の流れの可視化と速度分布測定に関する研究
    雪印メグミルク株式会社：
    研究期間 : 2018年07月 -2021年03月 
    代表者 : 村井祐一, 朴炫珍, 芳田泰基, 田坂裕司
  • 日本学術振興会：科研費 基盤研究(A)
    研究期間 : 2017年04月 -2021年03月 
    代表者 : 村井祐一
  • 流況可視化機能をもつリアルタイム超音波パルス混相流量計の開発
    新エネルギー研究開発機構(NEDO)：先導研究プログラム
    研究期間 : 2019年06月 -2020年10月 
    代表者 : 村井祐一,田坂裕司,朴炫珍
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 熊谷 一郎, 村井 祐一, 藤本 修平
     
    地球に優しい船舶抵抗低減技術である翼型気泡発生装置に関する実験研究を行った。海上技術安全研究所の高速流路を用いた空気導入性能試験では、高速領域(9m/s)において最大50 l/minの空気導入を確認できた。翼の負圧による空気導入モードには少なくとも3種あり、10ノットを超える高速流の場合、翼上面にキャビティが形成された．またキャビティ形成による空気導入性能の低下が確認された。さらに、同研究所の400ｍ水槽における36ｍモデル船を用いた曳航水槽実験においては、正味抵抗低減効果が最大となる最適な船速が存在し、約10ノットの船速において最大12％程度の正味抵抗低減効果が得られることが明らかになった。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2016年04月 -2019年03月 
    代表者 : 田坂 裕司, 村井 祐一, 中野 直人, ペクシーノ ジョルジ, ボックス フィン, ムリン トム
     
    円管内流れの亜臨界遷移問題に対し，シンセティックジェットアクチュエータを攪乱発生器として用いることで，ヘアピン渦列をその個数など制御しつつ攪乱として与え，遷移過程を観察した．その結果として，攪乱の振幅や周波数に対する特段の効果は観察されなかったが，ヘアピンの個数が少ない場合，乱流塊の形成に対して個数による有意な差が見られた．その他，気泡を管壁に貼り付けることで孤立乱流塊の自己維持機構に変調を与え，効果的に乱流塊へ再層流化をもたらすことができることを見いだした．そのメカニズムとして，気泡が存在することによる偏流，および気泡表面でのスリップによる変曲点型速度分布の変形が挙げられる．
  • マイクロバブルの乱流境界層中への混入による摩擦抵抗の低減
    防衛装備庁：安全保障技術研究推進制度
    研究期間 : 2016年09月 -2018年03月 
    代表者 : 村井祐一
  • 日本学術振興会：科研費 挑戦的萌芽研究：
    研究期間 : 2015年04月 -2017年03月 
    代表者 : 村井 祐一
  • 日本学術振興会：科研費 基盤研究(A)
    研究期間 : 2012年04月 -2017年03月 
    代表者 : 村井 祐一
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 田坂 裕司, 村井 祐一
     
    攪乱の添加により突発的に乱流遷移が生じる管内流れにおいて，局所乱流塊である乱流パフの遷移過程と遷移条件に着目して研究を進めた．(1)ピストン・シリンダ駆動による管内流れ装置（管長8m，管内径32mm）を開発し，自然遷移レイノルズ数25,000以上を実現した．(2)乱流パフ内の渦構造を効果的に抽出する可視化画像処理計測法を開発した．実験を通し，(3)過去の代表者らの研究で得られた，複雑な層流-乱流界面の再現とそれらが内包する物理的意味を明らかにするとともに，(4)マイクロバブルの混入が乱流遷移に与える影響を統計評価した．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2013年04月 -2016年03月 
    代表者 : 熊谷 一郎, 村井 祐一, 田坂 裕司
     
    変形可能な透明ゲルビーズを用いて固液混合マグマのアナログ物質を作成し、その非ニュートン流体のレオロジー特性の計測やマグマの流れを模擬した対流実験を行った。実験では、密度の異なる流体を一定流量注入したり、一定熱流量で流体を加熱したりすることでプルーム（対流）を作成した。その結果、ニュートン流体を用いた実験では見られなかった流れの局在化や間欠性が自発的に生じることを示した。これらの知見によって、火山活動の時空間分布（間欠性や局在化）に関する観測結果を説明できることを示した。
  • 風車の長期的設計指針を決めるランドマークデザイン
    日本学術振興会：科研費 挑戦的萌芽研究
    研究期間 : 2011年04月 -2013年03月 
    代表者 : 村井 祐一
  • NEDO：産業技術研究助成事業
    研究期間 : 2008年06月 -2012年05月 
    代表者 : 村井 祐一
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2011年 -2012年 
    代表者 : 田坂 裕司, 村井 祐一
     
    気泡を用いた摩擦抵抗低減手法の高効率化を目指し,流れの理解と効率的な制御をもたらす計測手法の開発を行った.気液二相チャネル流れを用いた基礎実験により,注入した気泡がクラスター化する要因を気泡の2体干渉の観点から調べた.超音波を用いて気泡ならびに流れの変遷をモニタリングする手法を考案し,実験室レベルで使用可能なプロトタイプを製作した.また,これを実際の船舶に使用する際の問題点について検討した.
  • Large Flow Rate Type Bubble Generator
    研究期間 : 2008年 -2012年
  • 複素粘度解析によるマイクロバブル流体の不可説明要因の一掃
    日本学術振興会：科研費 基盤研究(B)
    研究期間 : 2009年04月 -2011年03月 
    代表者 : 村井 祐一
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2008年 -2010年 
    代表者 : 二川 正敏, 長谷川 勝一, 金子 暁子, 羽賀 勝洋, 粉川 広行, 井田 真人, 直江 崇, 松本 洋一郎, 沖田 浩平, 田中 伸厚, 竹村 文夫, 岡本 孝司, 村井 祐一
     
    本研究では、ガスマイクロバブルを注入することにより、核破砕中性子源の水銀標的内に生じる圧力波を低減するためのメカニズムを定量的に究明し、実用的な防護策を構築することを目的として、マイクロバブル生成技術、マイクロバブル群中における圧力波伝ぱ、マイクロバブル相互作用、マイクロバブルと固液界面損傷について検討し、MW級核破砕中性子源の実現に対して大きな障壁となるキャビテーションによる損傷を低減するための技術を構築した。
  • NEDO：産業技術研究助成事業
    研究期間 : 2005年07月 -2008年06月 
    代表者 : 村井 祐一
  • 日本学術振興会：科研費 若手研究(B)
    研究期間 : 2005年04月 -2008年03月 
    代表者 : 村井 祐一
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2006年 -2008年 
    代表者 : 武田 靖, 村井 祐一, 田坂 裕司
     
    気流の空間的構造を定量計測するPIV(Particle Image Velocimetry)を技術開発することを目的とし3年間の研究の実施を通じて多面的な成果を上げた. 大規模な気流計測における主要な問題は, 環境負荷の少ないトレーサを開発すること, ならびに三次元非定常構造を定量捕獲するための光学設計, さらには速度ベクトルデータの高密度化であった. 平成18年度は, トレーサの開発としWatermist法, Soap Bubble法, ならびにTuft Resonance法について検討を行い, さらにPIVに適合したトレーサの注入方法を設計・検定した. これと同時に300m規模の大気流動場を三次元計測する問題点提起実験を実施した. 平成19年度は開発したトレーサ注入法と光学系を実例計測によりデモンストレーション実験した. 計測対象は竜巻のPIV計測, 樹木や鉄塔をモデル化した透過性物体の周囲空間流動のPIV計測である. 平成20年度は大気ダウンバーストを室内モデル実験置換し, カラートモグラフィックPIV技術の実証実験を実施した. これらの開発の結果, 従来まで低密度データの2次元計測に制約されてきた気流構造計測が, 3次元高密度データ取得が可能となるに至った. また応用実験から気流のもつ固有の流動場が新たに発見され, これらについてのダイナミクスを論文等で発表した.
  • 光・画像計測を応用した気液二相壁面乱流の特徴抽出に関する研究
    文科省・核燃料サイクル開発機構：先行基礎工学研究
    研究期間 : 2003年09月 -2006年03月 
    代表者 : 村井 祐一
  • 気泡による高速せん断乱流のコントロール
    日本学術振興会：科研費 若手研究(A)
    研究期間 : 2003年04月 -2006年03月 
    代表者 : 村井 祐一
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2003年 -2005年 
    代表者 : 山本 富士夫, 村井 祐一
     
    本研究は、PIV (Particle Image Velocimetry:粒子画像流速測定法)を一つのシステムにステーションとして集約し、混相乱流構造の解明に応用したものである。実績として次の成果を得た。 A.PIV並列計算ステーションの構築に関する成果: A-1.サボニウス風車まわりの高い変形速度を有する流れ場を当研究室開発のVGT[速度勾配テンソル法]を用いて計測誌、NS方程式の数値解法と融合したPIV-CFDハイブリッド化により圧力場の計算を可能とした。 A-2.気泡流における気泡間の相互作用を3D-PTVを適用した結果、鉛直方向には吸引作用が、水平方向には反発作用が働くことを明らかにした。 A-3.ボイド率の高い気泡流の気泡画像のPIV/PTV計測から逆解析により連続相(液相)の流速を計算する方法を開発し、その性能を明らかにした。 B.気液二相乱流構造の解明に関する成果: B-1.高速高解像度ビデオカメラとせん断応力センサーとを同期させたシステムを構築し、PIV計測により壁面スライド気泡群がもたらす乱流せん断応力増減機構を解明した。 B-2.気泡流の実効粘性・乱流特性・変形付与粘性を回転二重円筒間のテイラー・クエット気泡流のPIV計測により調べ、特にリング渦の場合とらせん渦の場合の遷移について明らかにした。 B-3.壁面気液二相流境界層のレイノルズ応力分布をShallow Focal PTVシステムの構築により調べ、壁面せん断応力低減との関係を検討した。 B-4.ヘリカル管内気泡流・スラグ流の乱流構造の解明のため、CT画像計測システムを構築し、実験の結果、遠心力の効果による二次流れの形成と気泡分布について新しい知見を得た。 以上の成果は25編の学術論文として発表された。
  • Application of Ultrasonic Doppler Velocimetry
    研究期間 : 2003年
  • 分散性混相流における乱流構造の解明とその応用技術の提案
    日本学術振興会：海外特別研究員
    研究期間 : 2001年03月 -2002年03月 
    代表者 : 村井 祐一
  • CFDとPIVを併用した固気液三相流の高精細解析
    文科省：科研費 奨励研究(A)
    研究期間 : 1999年04月 -2001年03月 
    代表者 : 村井 祐一
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1998年 -2000年 
    代表者 : 山本 富士夫, 村井 祐一, 太田 淳一
     
    環境汚染物質の除去装置,化学反応装置,微小重力環境装置,半導体デバイス,バイオテクノロジーなどの分野では,流動現象のマイクロメカニズムが機器の性能を左右する重要な問題となっている.本研究課題では,これをPIV(Particle Image Velocimetry:粒子画像流速測定法)により明らかにすることを目的として,PIVシステムの開発に専念してきた.本研究課題に対する3年間の研究成果は次の3つの項目に分けられる. 山本は,デローニ三角分割PTV法(DT-PTV),速度勾配テンソルPTV法(VGT),ならびにFuzzy Logic(FLPTV)を導入したPTV法のアルゴリズム開発を行った.DT-PTVでは従来型アルゴリズムの500倍程度の処理速度を実現し,VGTでは,回転・せん断などの変形自由度に対処した計測を実現し,いずれもExp.Fluidsに掲載された.Fuzzy Logicを併用した手法では,可視化画像からの粒子位置の認識と乱れ度の大きな流動に対して従来法よりも大幅に測定精度の向上が実現することを示した. 太田は,微小流路内の表面張力駆動流れ,自由噴流ならびに脈動噴流における局所的乱流構造に関するLDVとPIVの精度比較,ホログラフィによる微小空間流動の三次元PIV計測方法についてシステムを開発した.この中で,微小流路内では気液界面の存在が二次流れを誘発し,流動抵抗を増加させること,重ね合わせ法によるPIVによりLDVにひけをとらない流動計測精度を得ることを示した. 村井は,PIV手法の気泡流への応用と新しいPIVデータの後処理手法を開発した.これにより,気泡流中で微小な乱れが増幅する「逆エネルギーカスケード」現象,気泡プルームの三次元螺旋構造,物体周りの二相流の特異な伴流構造を定量的に解明することに成功した.これらの成果は,Exp.Fluidsを初めとする国際学術雑誌に発表され,内外から大きな反響があった. 以上,本課題の遂行によりこの技術を応用した新技術の創出,環境対策や安全性向上のための基盤が確立され,今後もさらに発展の期待できる成果を得た.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1996年 -1998年 
    代表者 : 小林 敏雄, 高木 周, 大島 まり, 佐賀 徹雄, 谷口 伸行, 村井 祐一
     
    本研究では、分散系の混相流についてLESにおけるモデル化を試み、その評価と最適化を主に数値シミュレーションにより行うことを目的とした。混相流モデリングに際しては、気泡の流動・変形の直接シミュレーションにより媒質流体への影響や気泡間の干渉を検証し、また、固気混相流での乱流変調の予測を主な課題として取り上げた。LESにおける定式化としては、分散粒子をラグランジュ的に扱う方法と統計平均方程式により分布を2種類の計算方法の可能性を検討した上で数値検証などによってそれぞれの得失を明らかにし,後者に基づくLES解析法を構築した。これらの数値シミュレーションに基づく結果は、DNSデータおよび画像処理計測による計測データによって、個々の粒子運動と混和流全体として流動状態の2つのレベルにおいて検証された。対象流れ場としては、混合層、2次元ジェット、チャンネル流などで層流状態から乱流となる比較的高レイノルズ数範囲を対象として基本的条件での詳細な検証を行い、分散系混和流動に適用しうる普遍的な知見として、特に、気泡流、および、固気混相流に関して以下を得た。 1)気泡運動の詳細モデリングとLES空間平均における分散相への寄与を考慮した気泡乱流LESモデルにより、気泡径の違いが乱流渦気泡輸送や浮力効果にあたえる影響を解析された。 2)固気相間の相互干渉を考慮した乱流LESモデリングによりサブグリッドスケールにおける散逸は適切にモデル化されている一方、グリッドスケール散逸機構については従来の粒子モデルでは必ずしも再現されない。 これらの上記研究結果から分散粒子混相乱流のLESモデリングの有効性が確認されるとともに、乱流現象と粒子分布生成の時間スケール、空間スケールの比が粒子ー流体カップリングモデルとその解析法の最適化において考慮されるべきことが示された。
  • Study on Turbulent Frictional Drag Reduction
    研究期間 : 1998年
  • Innvation of wind power generation technology
    研究期間 : 1998年
  • 気泡流乱流中の微細流動構造の数値解析・画像解析
    文科省：科研費 奨励研究(A)
    研究期間 : 1996年04月 -1997年03月 
    代表者 : 村井 祐一
  • 気液二相流の微細構造シミュレーション
    日本学術振興会：特別研究員 DC1（東京大学）
    研究期間 : 1995年04月 -1997年03月 
    代表者 : 村井 祐一
  • Development of PIV system
    研究期間 : 1992年
  • Multiphase Science and Technology
    研究期間 : 1988年

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  • 特許 米国:No. US7500837B2:Small size gear pump    2009年03月10日
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社会貢献活動

  • 泡が地球温暖化を抑える
    期間 : 2017年07月
    役割 : 実演
    主催者・発行元 : 東京国立科学博物館 機械学会賞受賞記念長期出典

メディア報道

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

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