JSME International Journal Series B Fluids and Thermal Engineering
Online ISSN : 1347-5371
Print ISSN : 1340-8054
ISSN-L : 1340-8054
PAPERS
Lock-in Phenomenon of Pitching Hydrofoil with Cavitation Breakdown
(Unsteady Fluid Force Characteristics and Visualization of Flow Structure)
Kazuhiko KATOHirotaka DANYasuaki MATSUDAIRA
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2006 Volume 49 Issue 3 Pages 797-805

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Abstract

The violent cavitation breakdown occurs periodically during vortex cavitation shedding when a sheet cavity elongates near the trailing edge of a hydrofoil. This causes unsteady and nonlinear fluid forces to act on the hydrofoil. This nonlinear behavior, when the breakdown frequency locks at the pitching frequency of the cavitating hydrofoil, has not yet been clarified. The unsteady lift coefficient and the flow structure of a pitching NACA hydrofoil under the lock-in phenomenon were clarified by load cell measurement and particle and bubble image processing for PIV. As the main result, in the Subcavitation region, when the elongation of the sheet cavity cannot follow the variation of the pitching angle at a highly reduced frequency, the pitching lift coefficient is offset similar to that of nonpitching oscillation. In the Transition region where cavitation breakdown frequently occurs, the reduced frequency range for the pitching lift coefficient can be characterized roughly into the Unlock-in, Quasi-lock-in and Lock-in ranges according to whether or not the breakdown frequency is synchronized with the pitching frequency.

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© 2006 by The Japan Society of Mechanical Engineers
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