Maximization of frictional drag reduction effect by coarseness and fineness distributed bubbles using multiphase turbulent shear stress meter

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K04255
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 19010:Fluid engineering-related
• Research Institution: Muroran Institute of Technology
• Principal Investigator: Yoshihiko Oishi 室蘭工業大学, 大学院工学研究科, 准教授 (90617078)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 抵抗低減 / 気泡 / せん断応力 / 省エネルギー技術 / 船舶 / 乱流 / 乱流境界層

Outline of Final Research Achievements

If we can establish a high-frequency-response fluid friction measurement that can observe individual bubbles and the flow around them, we can control the factors that increase the frictional resistance. The purpose of this research project is to independently establish a shear stress measurement method with high temporal resolution in multiphase flow and to demonstrate it under bubbly flow conditions. A high time-resolved laser shear stress meter was developed, and the shear stress when bubbles were mixed was successfully measured. We ensured that not only instantaneous fluctuations in shear stress but also average values could be measured. We challenged the extraction method of turbulence events, added an algorithm with conditional sampling, and analyzed changes in turbulence events. From this, it was found that the bubbly flow greatly contributes to the burst phenomenon.

Free Research Field

流体工学

Academic Significance and Societal Importance of the Research Achievements

本研究成果は先進的なせん断応力測定を介して，流体の輸送に関する問題を解決ための技術基盤を構築した．乱流中における気泡流という複雑な流動場の高時間分解での計測により摩擦抵抗低減を効果的に実現するためのメカニズム解明に寄与する．本課題解決により，船舶における摩擦抵抗低減の最大化に最も貢献する．せん断応力は船舶の輸送効率を決定する対水速度計測の目となり，自動化など波及効果が高い．さらに，乱流中における気泡流の測定が可能になったことで，非ニュートン流体など様々な流体の直接測定の可能性を広げた．