Propeller tip vortex cavitation control and induced noise suppression by water injection

Abstract

As noise emission from ships garners increasing interest, control of propeller cavitation, which generates vibration and radiates noise, gains critical importance. In the case of full-scale propellers, the tip vortex cavitation typically incepts first, and noise levels rise dramatically thereafter. We propose the mass injection method to reduce noise induced from the tip vortex cavitation and increase the cavity inception speed. Water injected from the propeller tip decreases the rotational speed of the tip flow, and restrains the growth of the tip vortex cavity. For the preliminary test, we investigate the flow around an elliptic wing in a cavitation tunnel, and measured the induced noise levels. The results show a clear decrease in the noise levels in the case of water injection from the wing tip compared to that of without injection. On the basis of a successful preliminary study, we apply this method to the rotating model propeller. Experimental investigations of the model tests in a large cavitation tunnel show that we can control the tip vortex cavitation of the propeller, and hence, increase the cavitation inception speed of the ship using water injection from the propeller tip.