Development of control method of structures in turbulent boundary layer using artificial void wave

2018 Fiscal Year Final Research Report

• Project/Area Number: 17K14583
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Fluid engineering
• 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): 2017-04-01 – 2019-03-31
• Keywords: 乱流境界層制御 / 気液二相流 / 抵抗低減 / ボイド波

Outline of Final Research Achievements

Until now, a bubbly drag reduction technique for fuel saving of large vessels has been try to control with a fixed void fraction to achieve high drag reduction rate stably, but this trial is failed. It is because bubbly drag reduction is a non-linear function to void fraction. I found that the drag reduction can be promoted by artificial void waves injected into a turbulent boundary layer and developed improving drag reduction rate technique, named as a repetitive bubble injection(RBI). In this study, characteristics of void waves were estimated and a specific void wave was discussed to improve it. By the estimation, the specific void wave having a natural void wave frequency was suggested to achieve the maximum drag reduction rate and can be maintained for a long distance .

Free Research Field

流体工学

Academic Significance and Societal Importance of the Research Achievements

従来の気泡注入法(CBI)により抵抗低減を得る際に，船低を流れる気泡を可視化した結果，下流でボイド波が自然に発達することが確認された．RBIを用いてこの自然ボイド波と同様な周波数を人工ボイド波を境界層に注入すると，長距離においてボイド波を維持できることが本研究で確認された．さらに自然周波数でRBIを行った際に，抵抗低減率が最大になった．本研究により，RBIで船底の広範囲において提案する高い抵抗低減率を有する人工ボイド波を安定的に与えることができれば，船舶の燃費が大幅に改善する．