1988 Fiscal Year Final Research Report Summary
Research on Clond Cavitation
| Project/Area Number |
61420033
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
船舶抵抗・運動性能・計画
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| Research Institution | The University of Tokyo |
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Principal Investigator |
KATO Hiroharu The University of Tokyo, 工学部, 教授 (00010695)
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| Co-Investigator(Kenkyū-buntansha) |
WATANABE Yakou The University of Tokyo, 工学部, 助手 (00010893)
YAMAGUCHI Hajime The University of Tokyo, 工学部, 助教授 (20166622)
KINOSHITA Takeshi Institute of Industrial Science University of Tokyo, 生産技術研究所, 助教授 (70107366)
MIYATA Hideaki The University of Tokyo, 工学部, 助教授 (70111474)
KAJITANI Hisashi The University of Tokyo, 工学部, 教授 (80010693)
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| Project Period (FY) |
1986 – 1988
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| Keywords | Cavitation / Cloud Cavitation / Laser Holography / Hydrofoil / Bubbly Flow / 数値流体力学 |
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| Research Abstract |
This research dealt with unsteady sheet and cloud cavitation generated on a steady 2-dimensional hydrofoil. The outline of the results is as follows:
1. Velocity distribution around a cavitation cloud was measured by conditionally sampling the output signal of a laser doppler velocimeter and the high-speed photograph of the cavitation based on the unsteady pressure on the hydrofoil. The result showed that the cloud cavitation was a phenomenon where many bubbles were taken in a large vortex induced by the cavity itself and collapsed there, revealing that the fluid vortex motion is closely related to all its generation, growth and collapse.
2. A laser holography method was applied to measure the cluster of bubbles inside a cavitation cloud and downstream of a stable sheet cavity. As a result the three dimensional structure of the cavitating vortices inside the cavitation cloud and the spatial distribution of spherical bubbles were measured. 30-40 m was the smallest diameter of bubbles that could be recognized clearly. Application of image proccssing technique was tried in the analyses.
3. The time variation of cavity size measured by the high-speed photograph was synchronized with that of lift coefficient measured by a three component load cell. The result showed that the cavity grew monotonously and was suddenly broken off resulting in shedding the cavitation cloud while the lift coeffecient increased first and then decreased. When the cavity was broken off, the time derivative of the lift coeffecient was negative.
4. A numerical calculation of unsteady cavitation was made using a bubble two phase flow model, a new cavity flow model. The result showed that the behaviour of the shear layer sparated at the cavity leading edge was closely related to the generation of cloud cavitation. The present flow model may lead to highly accurate numerical prediction of unsteady sheet and cloud cavitation.
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