2019 Fiscal Year Final Research Report
Development of general-purpose hydrofoil bubble generators for ship drag reduction toward practical application to deep-draft ships
| Project/Area Number |
17H03499
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Naval and maritime engineering
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| Research Institution | Meisei University |
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Principal Investigator |
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| Co-Investigator(Kenkyū-buntansha) |
村井 祐一 北海道大学, 工学研究院, 教授 (80273001)
藤本 修平 国立研究開発法人海上・港湾・航空技術研究所, その他部局等, 研究員 (80586686)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | 船舶抵抗低減 / 気液二相流 / 可視化 |
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| Outline of Final Research Achievements |
As an Earth-friendly tool, we invented a hydrofoil bubble generator to reduce ship drag and conducted experiments using a high-speed channel tunnel in National Maritime Research Institute (NMRI) to understand the behaviors of air bubble generation at a cruising speed up to 20 knots. The threshold of air entrainment, the air flow rate, and the bubbly flow pattern depend on Reynolds number, angle of attack, and hydrofoil type. We identified intermittent air entrainment at a low-speed condition, stable air entrainment, and air entrainment with a ventilated cavity at a high-speed condition (> 5m/s). Although the ventilated cavity lowers the ability of air entrainment, a large volume of air bubbles (50 l/min) was generated by the hydrofoil system at 9 m/s, which has a high potential to reduce ship drag. We have also conducted a towing tank experiments using a 400m tank in NMRI and obtained the maximum net drag reduction (about 12%) for a 36m model ship at a cursing speed (10 knots).
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| Free Research Field |
流体工学
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| Academic Significance and Societal Importance of the Research Achievements |
翼型気泡発生装置に関する実験は、これまで約６ノットが最速であった。本研究の高速流路を用いた実験によって、約２０ノットの高速領域まで、その空気導入性能や壁面近傍の気泡流の挙動が明らかになった。これまで、船速が速ければ速いほど、高い正味抵抗低減効果が得られると考えられてきたが、海技研の４００ｍ曳航水槽を用いた実験成果により、最適な船速（約１０ノットで１２％の正味抵抗低減効果）が存在することが初めて明らかになった。また、導入空気の流体力学的微細化技術によって、より少ない空気流量で高い抵抗低減効果を実現できた。これにより、深喫水船で使用する空気ポンプをアシストし、さらなる省エネが可能となった。
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