Design and Evaluation of New Supercavitating Propeller

Abstract

This paper firstly describes a new design method of supercavitating (hereafter, SC) propellers. The circulation distribution of propeller blades was calculated by a lifting line theory as an existing method, while the hydrodynamic characteristics of blade sections at each radial position were calculated by a nonlinear cavity flow theory based on a higher-order singularity panel method, “Linear Vortex Panel Method ; LVPM”.Three SC propellers were designed for the same design conditions, that is, the ship speed is 50 kts, the required thrust per shaft is 100 tons and the propeller immersion is 4 meters. The SSPA SC propeller was chosen as a target SC propeller, since reliable design charts were published. The optimum propeller revolution rate was determined from the chart under the constrained condition of supercavitation. For the target propeller, a SSPA propeller model was made and the hydrodynamic characteristics were measured in the SRI large cavitation tunnel.From the calculated circulation distribution and the assumed blade contour, the design lift coefficient at each radial position and SC section were determined by the iteration so that the strength requirement was satisfied. The lifting surface correction based on Ludwieg-Ginzel's method was applied to the blade profile on the face side of the first designed SC propeller (SRIJ-I). The efficiency of the SRIJ-I SC propeller at the design condition (J=1.1) was 0.676 and about 4 % higher than the target propeller. The measured thrust of the SRIJ-I SC propeller was 15 % higher than the predicted one and this propeller emitted relatively higher cavitation noise.Secondly effort was made to improve the performance of the first designed SC propeller. From the examination by the experiments, inappropriate camber correction was cleared up. Using the load distribution of the SC sections given by the LVPM, the camber distribution at each radial position was calculated by the propeller design method based on “Quasi-Continuous Method”. The second SC propeller was tested at the cavitation tunnel. The measured propeller efficiency at the design condition was 0.720 and the increase of 11 % on the efficiency was obtained against the target propeller. The obtained thrust was 4 % higher than the predicted one, while the propeller was fully cavitating. It is concluded that a new favorable SC propeller could be designed by the present design method.