A semi-empirical method to predict broadband hull pressure fluctuations and underwater radiated noise by cavitating tip vortices

A semi-empirical method is presented that predicts broadband hull pressure fluctuations and underwater radiated noise due to propeller tip vortex cavitation. The method uses a hump-shaped pattern for the spectrum and it predicts the center frequency and level of this hump. The principal parameter is the vortex cavity size which is predicted using a combination of a boundary element method and a semi-empirical vortex model. It is shown that such a model is able to well represent the variation of cavity size with cavitation number. Using a database of model-scale and full-scale measured hull pressure data, an empirical formulation for the center frequency and level has been developed that is a function of among others the cavity size. Predicted and measured hull pressure and radiated noise spectra are compared for various cases. Acceptable results are obtained but the comparison also shows differences that require adjustments of parameters which need to be further investigated.