Flow Field Measurement around a Marine Propeller by Laser Doppler Velocimeter

Abstract

Measurement of flow velocity distribution around a marine propeller was carried out by Laser Doppler Velocimeter (LDV) in a cavitation tunnel. An LDV measurement system which can supply both velocity data and measuring position data relative to the blade was developed, and the information about instantaneous velocity distribution around propeller blades was obtained. Authors succeeded in revealing the vortex system around propeller blades. The effect of a strong vortex extending from blade tip was recognized in the measured velocity data. Accelerated and contracted flow behind blades was also observed. Thrust and torque estimated from velocity distribution in slip stream were compared with direct measurement results. Comparison between experimental results and lifting surface theory shows that the existence of strong tip vortices shown by the experiment can not be followed by the theory. It is necessary to investigate a separated flow in the region near the blade tip, in order to improve the theoretical method.