2006 Fiscal Year Final Research Report Summary
Development of a simulator of the microbubble drag reduction
| Project/Area Number |
17560704
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | University of Tokyo |
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Principal Investigator |
YAMAGUCH Hajime University of Tokyo, Department of Environmental and Ocean Engineering・Graduate School of Engineering, Professor, 大学院・工学系研究科, 教授 (20166622)
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| Co-Investigator(Kenkyū-buntansha) |
KAWAMURA Takafumi University of Tokyo, Department of Environmental and Ocean Engineering・Graduate School of Engineering, Associate Professor, 大学院・工学系研究科, 助教授 (80334324)
MAEDA Masatsugu University of Tokyo, Department of Environmental and Ocean Engineering・Graduate School of Engineering, Research Associate, 大学院・工学系研究科, 助手 (60219277)
MIYANAGA Masaru University of Tokyo, Department of Environmental and Ocean Engineering・Graduate School of Engineering, Research Assistant, 大学院・工学系研究科, 技術職員 (00401133)
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| Project Period (FY) |
2005 – 2006
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| Keywords | microbubble / numerical simulation / multiphase flow / drag reduction / propeller |
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| Research Abstract |
Injection of air bubbles into the turbulent boundary layer around a ship can reduce the propulsion resistance of the ship through reducing the frictional drag. It has been confirmed in recent full scale experiments that net energy saving of about 5% can be achieved by the bubble injection. However, the full scale experiments also suggested that the injection of bubbles degrades the propeller efficiency.
The purpose of this study is to develop a numerical model which can predict the propeller efficiency in bubbly flow and to elucidate the mechanism of the reduction inefficiency. The model is a two-fluid multiphase flow model of which the governing equations are the mass and momentum conservation of the mixture and the bubble phases, and the key is to correctly account for the various forces which governs the motion of bubbles. The model was tuned using experimental data for 2D hydrofoils and a propeller in bubbly flows, and a good agreement was achieved.
The results of the simulation were investigated in detail in order to explain the decrease in the efficiency. It was shown that bubbles are relatively accelerated around the leading edge of a hydrofoil or a propeller blade, and that the acceleration of liquid is reduced due to the bubble acceleration. This effect lowers the peak of the negative pressure at the leading edge resulting in the decrease in the lift and the increase in the drag coefficients.
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Research Products
(9 results)
