| Abstract | Over the last few decades, several attempts have been made by maritime R&D to obtain higher propulsive efficiencies and lower cavitation and pressure pulses (and hence underwater radiated noise, URN) by skewing the propeller blades and radically modifying the geometry in the blade tip region. Efforts to design such high-skewed tip-raked propellers focused mainly on increasing the propeller’s efficiency, with little to no attention given to minimizing the cavitation and URN. This work was initiated to develop tools for evaluating the propulsive and cavitation performance of a conventional and a highly-skewed propeller, with and without the tip-rake of different magnitudes and orientations, all designed for the same operating conditions. The authors used an existing in-house numerical codebase, PaTH-AC, capable of predicting the hydrodynamic performance of screw propellers, as a primary tool for the investigation. The radial skew distributions and the rake around the blade tip are varied systematically, and their effects are evaluated using PaTH-AC analysis for open water and cavitation performance. The evaluated variants include forwardraked and aftward-raked propellers with and without specific skew distributions.
The predictions of the open water performance of a Base propeller have been validated using both basin measurements and high-fidelity RANS simulations in the corresponding operating conditions. The RANS predicted thrust and torque of the highly-skewed Base propeller compare well with the corresponding measurements; however, the PaTH-AC results show slight over-predictions of both thrust and torque. Additionally, RANS simulations were carried out for one case of a tip-rake propeller, which was used to validate the PaTH-AC predictions. Overall, the results of the predictions show better propulsive performance of the forward-raked propellers, particularly with moderate rake change at the tip. In light loading conditions, RANS and PaTH-AC predicted similar blade tip and pressure side sheet cavitation. The PaTH-AC is currently being further developed for more accurate cavitation predictions and to predict the URN induced by the propellers using the predicted pressure field on the blade surface. The results presented here are considered preliminary. |
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