The present study deals with the shedding process of the von Kármán vortices at the trailing edge of a 2D hydrofoil at high Reynolds number Reh=25×103–65×103. This research focuses mainly on the effects of cavitation and fluid-structure interaction on the mechanism of the vortex generation. The vortex shedding frequency, derived from the flow-induced vibration measurement, is found to follow the Strouhal law provided that no hydrofoil resonance frequencies are excited, i.e., lock-off. For such a regime, the von Kármán vortices exhibit strong spanwise 3D instabilities and the cavitation inception index is linearly dependent on the square root of the Reynolds number. In the case of resonance, the vortex shedding frequency is locked onto the hydrofoil eigenfrequency and the spatial coherence is enhanced with a quasi-2D shape. The measurements of the hydrofoil wall velocity amplitude and phase reveal the first torsion eigenmotion. In this case, the cavitation inception index is found to be significantly increased compared to lock-off conditions. It makes clear that the vortex roll-up is amplified by the phase locked vibrations of the trailing edge. For the cavitation inception index, a new correlation relationship that encompasses the entire range of Reynolds numbers, including both the lock-off and the lock-in cases, is proposed and validated. In contrast to the earlier models, the new correlation takes into account the trailing edge displacement velocity. In addition, it is found that the transverse velocity of the trailing edge increases the vortex strength linearly. This effect is important in the context of the fluid-structure interaction, since it implies that the velocity of the hydrofoil trailing edge increases the fluctuating forces on the body. It is also demonstrated that cavitation developing in the vortex street cannot be considered as a passive agent for the turbulent wake flow. In fact, for fully developed cavitation, the vortex shedding frequency increases up to 15%, which is accompanied by the increase of the vortex advection velocity and reduction of the streamwise vortex spacing. In addition, a significant increase of the vortex-induced vibration level is found at cavitation onset. These effects are addressed and thought to be a result of the increase of the vorticity by cavitation.
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e-mail: francois.avellan@epfl.ch
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August 2007
Technical Papers
Cavitation Influence on von Kármán Vortex Shedding and Induced Hydrofoil Vibrations
Philippe Ausoni,
Philippe Ausoni
Laboratory for Hydraulic Machines
, EPFL, Ecole polytechnique fédérale de Lausanne, Avenue de Cour 33bis, 1007 Lausanne, Switzerland
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Mohamed Farhat,
Mohamed Farhat
Laboratory for Hydraulic Machines
, EPFL, Ecole polytechnique fédérale de Lausanne, Avenue de Cour 33bis, 1007 Lausanne, Switzerland
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Xavier Escaler,
Xavier Escaler
Center for Industrial Diagnostics, UPC,
Universitat Politecnica de Catalunya
, Avenidad Diagonal 647, 08028 Barcelona, Spain
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Eduard Egusquiza,
Eduard Egusquiza
Center for Industrial Diagnostics, UPC,
Universitat Politecnica de Catalunya
, Avenidad Diagonal 647, 08028 Barcelona, Spain
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François Avellan
e-mail: francois.avellan@epfl.ch
François Avellan
Laboratory for Hydraulic Machines
, EPFL, Ecole polytechnique fédérale de Lausanne, Avenue de Cour 33bis, 1007 Lausanne, Switzerland
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Philippe Ausoni
Laboratory for Hydraulic Machines
, EPFL, Ecole polytechnique fédérale de Lausanne, Avenue de Cour 33bis, 1007 Lausanne, Switzerland
Mohamed Farhat
Laboratory for Hydraulic Machines
, EPFL, Ecole polytechnique fédérale de Lausanne, Avenue de Cour 33bis, 1007 Lausanne, Switzerland
Xavier Escaler
Center for Industrial Diagnostics, UPC,
Universitat Politecnica de Catalunya
, Avenidad Diagonal 647, 08028 Barcelona, Spain
Eduard Egusquiza
Center for Industrial Diagnostics, UPC,
Universitat Politecnica de Catalunya
, Avenidad Diagonal 647, 08028 Barcelona, Spain
François Avellan
Laboratory for Hydraulic Machines
, EPFL, Ecole polytechnique fédérale de Lausanne, Avenue de Cour 33bis, 1007 Lausanne, Switzerlande-mail: francois.avellan@epfl.ch
J. Fluids Eng. Aug 2007, 129(8): 966-973 (8 pages)
Published Online: March 16, 2007
Article history
Received:
June 27, 2006
Revised:
March 16, 2007
Citation
Ausoni, P., Farhat, M., Escaler, X., Egusquiza, E., and Avellan, F. (March 16, 2007). "Cavitation Influence on von Kármán Vortex Shedding and Induced Hydrofoil Vibrations." ASME. J. Fluids Eng. August 2007; 129(8): 966–973. https://doi.org/10.1115/1.2746907
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