| Project/Area Number |
21K14069
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| Research Category |
Grant-in-Aid for Early-Career Scientists
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| Allocation Type | Multi-year Fund |
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| Review Section |
Basic Section 19010:Fluid engineering-related
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| Research Institution | Hokkaido University |
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Principal Investigator |
Park Hyun Jin 北海道大学, 工学研究院, 助教 (00793671)
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| Project Period (FY) |
2021-04-01 – 2023-03-31
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| Project Status |
Completed (Fiscal Year 2022)
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| Budget Amount *help |
¥4,680,000 (Direct Cost: ¥3,600,000、Indirect Cost: ¥1,080,000)
Fiscal Year 2022: ¥2,340,000 (Direct Cost: ¥1,800,000、Indirect Cost: ¥540,000)
Fiscal Year 2021: ¥2,340,000 (Direct Cost: ¥1,800,000、Indirect Cost: ¥540,000)
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| Keywords | 混相流 / 抵抗低減 / 気泡 / 船舶 / 気液混相流 / ボイド波 |
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| Outline of Research at the Start |
乱流境界層に気泡を混入し摩擦を減らす空気潤滑法は，低い再現性と下流持続性が問題であり，約10%省エネで頭打ちしている．申請者は，境界層に人工的な脈動を与え再現性と下流持続性を改善する方法を開発した．この改善法を活用するには，境界層の状態に合わせて抵抗低減率が高い脈動を予め特定する必要があるが，脈動に関わる主要因子すら不明である．本研究では，境界層に与えた人工脈動が移流中に示す脈動の挙動と境界層の応答を調べることで，脈動と乱流境界層との間に生じる物理現象の解明と脈動成長過程のモデリングを行う．成長モデルを逆算することで脈動制御技術を完成させ，人工脈動による高効率抵抗低減法の基盤を作る．
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| 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.
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| 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．
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