Flow-induced vibration of flexible tapering hydrofoils with and without sheet cavitation

Abstract

In this paper, we study the fluid–structure interaction (FSI) of a flexible cantilevered tapering hydrofoil in cavitating turbulent flows. We consider a recently developed variational cavitation FSI solver employing a large-eddy simulation model, a homogeneous mixture cavitation model, and the structural mode superposition method. Of particular interest is understanding the coupled dynamics of vortex shedding and cavitation around the hydrofoil and the mechanism responsible for the self-sustained structural vibration due to the vortex-cavitation interaction. In both the cavitating and non-cavitating cases, the structural vibrations generally exhibit the amplifying trend as the structure becomes less stiff, in both the in-line and transverse directions. When sheet cavitation appears on the suction side of the hydrofoil, the magnitude of structural fluctuation is amplified nearly seven times while the average deformation remains weaker. To understand this amplification process, we systematically examine the synchronized hydroelastic coupling through pressure pulsation within the flow field, cavitation generation, and structural vibration. We find that the generation of sheet cavitation induces considerable hydrofoil vibration subjected to a flutter-like response with sustained oscillations, accompanied by the frequency lock-in behavior owing to the synchronization among the structural modes and the surface forces, as well as their harmonics. In addition, we observe that the generation of cavitation increases the structural natural frequency of the FSI system concerned.