Cavitation tunnel analysis of radiated sound from the resonance of a propeller tip vortex cavity

Abstract

The goal of this study is to test the hypothesis that the resonance of a tip vortex cavity is responsible for high-amplitude broadband pressure-fluctuations, typically between 40 and 70 Hz, for a full scale propeller. This is achieved with a model propeller in a cavitation tunnel. Simultaneous high-speed video shadowgraphy and sound measurements show that a steady tip-vortex cavity behind a propeller in a uniform inflow does not produce significant sound in the relevant range of 0.5-1.2 kHz. The addition of an upstream wake does result in high amplitude sound. It appears that the dominant sound frequency is directly related to the resonance of the tip vortex cavity. A model for the tip-vortex cavity-resonance frequency, using a Proctor vortex model, is able to give an accurate description of the dominant sound frequencies.