Numerical Model of Cavitating Propeller Inside of a Tunnel

Abstract

The unsteady cavitating flow of a propeller subject to a nonaxisymmetric inflow inside of a tunnel is addressed. A numerical method is developed which solves for the fully unsteady propeller problem and the tunnel problem separately, with the unsteady effects of one on the other being accounted for in an iterative manner. The propeller influence on the propeller is considered via velocity. The iterative process is found to converge very fast, usually within three iterations, even for a heavily loaded propeller. The effect of the tunnel extent and the number of panels on the predicted mean propeller forces is investigated. In the case of uniform inflow the equivalent open water velocity is calculated and then compared to that predicted from Glauert’s formula. The two velocities are found to be very close to each other in the case of light propeller loading, and to deviate from each other as the propeller loading increases. In the case of nonuniform flow the predicted unsteady propeller forces are found not to be affected appreciably by the tunnel effects in the case of noncavitating flow. In the case of cavitating flows the tunnel effects have been found to be appreciable, especially in terms of the predicted cavity extent and volume. The predicted cavity patterns are shown to be very close to those observed in CAPREX, a CAvitating PRopeller Experiment performed at MIT’s cavitation tunnel.