Predicting axial velocity profiles within a diffusing marine propeller jet

A full understanding of the hydrodynamic processes within the jet produced by a manoeuvring ship's propeller is essential in the development and maintenance of ports, docks and harbours. In this investigation the predominant axial velocity component within a freely expanding wash was studied. The flow fields formed by four propellers, each operating at four power levels (speeds of rotation), were investigated under bollard pull conditions and in the absence of a rudder, within a large free surface tank using Laser Doppler Anemometry. The characteristics of these propellers extended the range over which high accuracy measurements have been previously attempted. Comparison were made to existing methodologies by which a prediction of the magnitudes of the axial velocity can be made, and where deficient modifications to the methodologies have been developed and presented. The jets were found to produce a maximum axial velocity along the initial efflux plane at a location near the blade mid-span. The position and magnitude of the axial velocity was seen to decrease as the jet entrained more flow and transitioned from the zone of flow establishment into the zone of established flow.