(A) tip vortex suppression of a ducted propeller by mass injection

Abstract

Ducted propellers are the commonly used propulsion systems in many kinds of vessels, however, they can cause the cavitation inception problems, such as a vibration and an erosion, by the pressure drop of the vortex generated near a tip clearance. Therefore, this study applied the method called mass injection to ducted propellers for the vortex suppression near a tip clearance and devised the new shapes of ducts which have passages. The upstream can flow into the passages and be injected near a tip clearance, disturbing an internal flow. We experimentally investigated the vortex suppression by mass injection of the new ducts at the advance coefficients of 0.2, 0.4, and 0.6 by measuring the maximum vorticity and visualizing vortical structures in the wake. Mass injection is effective in suppressing the vortex generation at an advance coefficient of 0.2, but, the vortex is not properly suppressed with the increase in an advance coefficient. In addition, the effect of the new ducts on the propulsive performance was investigated by measuring the thrust and the torque, and the new ducts slightly changes the thrust but decrease the torque significantly, leading to an efficiency loss.