The effect of tip rake distribution on the hydrodynamic performance of shaftless rim-driven contra-rotating thruster

Shaftless rim-driven contra-rotating thruster (RDCRT) has recently become the research focus for marine propulsion, primarily due to low vibration, low overall torque, and energy saving as its advantage. This study applied 4-order B-spline theory to vary the rake distribution of the blade tip for a shaftless rim-driven thruster (RDT) originated from duct propeller Ka4-70+No.19A, and constructed four shaftless RDTs with different blade tip rakes. Through CFD simulation, the impact of blade tip rake on the open water performance, wake distribution, and sheet cavitation performance of the shaftless RDTs with single propeller were evaluated. On the basis of the above, we further compared the effect of tip rake on the open water performance, wake distribution, pressure distribution, and sheet cavitation performance of three shaftless RDCRTs. It was found that the tip rake inclined to the pressure side of shaftless RDCRT is in favor of both propulsion efficiency and anti-cavitation performance, while the tip rake inclined to the suction side adversely exerts opposite effects. With the aid of the tip rake inclined to the pressure side for the front and rear propellers, the maximum propulsion efficiency of shaftless RDCRT tends to rise by 2.6%, together with the wake stretching more uniformly. For shaftless RDCRT, the optimization design from the aspect of tip rake would be capable of validating its performance and advantages.