The Effect of Tip Rake on Propeller Induced Pressure Fluctuations

The authors propose a practical method to estimate the reduction rate of propeller-induced pressure fluctuations due to the backward rake around the blade tip. The designed geometrical shape of propeller blades decisively affects the propeller performance and the cavitation characteristics as well. The propeller designers try to reflect positive effects of the geometrical parameters to propeller design to enhance the propeller performance and to reduce the negative effects of cavitation behavior. In the present study, the cavitation tests and the measurement of pressure fluctuations induced by the respective propellers with five kinds of backward tip rake distribution working in the wake distribution behind an inland ship are performed systematically. The effects of the backward rake distribution on the pressure fluctuation signals are clearly demonstrated. The systematic analysis of the measured pressure fluctuations derives a practical formula to estimate the reduction rate of the pressure fluctuations due to the effective backward tip rake. Finally this formula is applied to the measured results of pressure fluctuations on other backward tip raked propellers working in the wake of a large low-speed ship to confirm its effectiveness. The results show that the present simple and practical method is promising but further validation is encouraged through the practical applications.