Experimental investigation of the hydrodynamic damping of a vibrating hydrofoil in cavitating flow

Abstract

To understand how cavitation affects underwater structure's vibration characteristics, an experiment on a vibrating hydrofoil is designed to quantitatively measure the flow-induced vibration, added mass, and hydrodynamic damping ratio in cavitating flow. The reliability of the experimental devices was verified, and the maximum cavity length and cavitation Strouhal number were in agreement with previously published experimental results. Regarding the flow-induced vibration, the resonance amplitude decreases with the cavitation development. Especially for the cavitation inception, the resonance amplitude decreases by 74% relative to that without cavitation. For the add mass coefficient, the linear relationship between it and maximum cavity length is established and is found to be independent of flow velocity, attack angle, and cavitation number. However, the effects of cavitation on the hydrodynamic damping are highly related to the flow condition. In particular, the hydrodynamic damping ratio decreases with increasing maximum cavity length when the velocity is above the resonance velocity, and the reduction reaches 39% if cavitation covers the hydrofoil completely. But this trend is inversed in the lock-in region. In addition, the hydrodynamic damping almost keeps constant when the velocity is below the resonance velocity.