Investigation of the resonance frequency of a cavitating vortex
Author Bosschers, J.
Title Investigation of the resonance frequency of a cavitating vortex
Conference/Journal NAG-DAGA International Conference on Acoustics
Month March
Year 2009
Pages 289-292

The cavitation pattern of a modern ship propeller is often characterized by a cavitating vortex. This cavitating vortex may generate (low frequency) hull pressure fluctuations which cause noise and vibration hindrance on board the ship. Existing measurement data of the pressure fluctuations suggest the presence of a resonance frequency, but detailed investigation is hindered by the highly intermittent character of the cavity. A distinct resonance frequency has been observed in the sound generated by a cavitating vortex trailing from a wing of elliptical planform in a cavitation tunnel by Maines & Arndt [JFE199-1997]. The paper will present a theoretical formulation for such a resonance frequency. The agreement between theory and experiment is good for low cavitation numbers but becomes less with increasing cavitation number. The theorically derived dispersion relation is based on the convected Helmholtz equation for a disturbance velocity potential and assumes an inviscid cavitating vortex which shows small deformations for prescribed oscillation modes. The dispersion relation is investigated with respect to phase speed and group speed. The first mode, a breathing mode, may have a zero group speed which is used to derive a unique relation between the non-dimensional (resonance) frequency and the cavitation number.

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