Wide-ranged turbulent flow control using singular pulsations appearing in the gas-liquid multiphase turbulent boundary layer

2022 Fiscal Year Final Research Report

• Project/Area Number: 21K14069
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 19010:Fluid engineering-related
• Research Institution: Hokkaido University
• Principal Investigator: Park Hyun Jin 北海道大学, 工学研究院, 助教 (00793671)
• Project Period (FY): 2021-04-01 – 2023-03-31
• Keywords: 混相流 / 抵抗低減 / 気泡 / 船舶

Outline of Final Research Achievements

For the understanding of the generation mechanism and propagation modeling of the spatio-temporal fluctuations of the void fraction, named as a void wave, that appears when the air lubrication reduces the wall frictional drag, experimental studies using rectangular channels having different cross-sectional shapes and model ships having a turbulent boundary layer on flat-plate. From the observation of void waves growing in different channels, it was found that the generation process of void waves and the growth of the turbulent boundary layer are involved in the generation of void waves. It was found that the drag reduction rate is improved by the artificial void wave where all areas of the ships except near the bubble injector. In addition, models that describe the propagation of the artificial void wave and the local drag reduction rate at the bottom of the ship with the air lubrication were constructed from experimental data.

Free Research Field

流体工学

Academic Significance and Societal Importance of the Research Achievements

抵抗低減率と人工ボイド波の下流持続性が確認され，さらにその伝播過程を記述するモデル式の構築により，船体における空気潤滑法がもたらす全摩擦抵抗低減率と人工ボイド波の抵抗低減促進効果を推定することが可能になった．また，ボイド波の生成条件と生成過程を把握できたことで，今後人工ボイド波を設計するための実験環境と計測すべき物理量が明確になった．