Scaling of Tip Vortex Cavitation Inception

Abstract

A practical method for predicting tip vortex cavitation inception of marine propellers is described. Cavitation of tip vortex first occurs when the local pressure inside the vortex reduces to the vapor pressure of the fluid. The minimum pressure in the vortex is reached at the radius of the viscous core. An expression for tip vortex cavitation inception number is derived based on a study of Hsu (1989). with the assumption of power-law circulation distribution. The radius of the viscous core in this approximation depends on the circulation distribution and diffusive action of the fluid viscosity. Accurate determinations of circulation distributions for propellers operating behind ships by purely theoretical means can be quite difficult. In the present paper a calculation procedure for estimating tip vortex cavitation inception number is outlined with the aid of model experimental data. Cavitation experiments of various model propeller in simulated full scale wake were carried out in the David Taylor Research Center 36-inch Variable Pressure Water Tunnel. Experimental data have been extensively analyzed and used for tip vortex cavitation inception predictions. Some comparisons between the present prediction method and ship trial data are made. with results in good agreement.