An Experimental Study of Air Injection Method on Ducted Propeller

Abstract

From a viewpoint of the improvement in the propulsive efficiency, the feasibility range of the ducted propeller is expected to increase to a great extent. On the other hand, the cavitation erosion on the duct inner surface has turned out to be a more serious problem than expected, and might be a fatal drawback to the ducted propeller without adequate countermeasures. As a solution to this problem, the air injection method has been introduced into practical use. This paper gives the results of experimental investigations into the effectiveness of this newly developed erosion protection method.To investigate the effect of the air injection, the following measurements have been performed on 230,000 DWT tankers in sea trials; 1. Cavitation observation 2. Noise radiated from cavitating propeller 3. Duct panel vibration 4. Hull vibration 5. Effect on ship speed and propeller revolution By these tests it has been proved that the air injection reduces remarkably the intensity of the response to the cavitation attack due to cavity collapse. The tests have also shown that there is no significant effect on the hull vibration and the propulsive performance. In the post-service erosion survey of the ducted propellers, the effectiveness of the air injection has also been confirmed.