Numerical research on mechanism of the effect of propeller shaft brackets on wake field and propulsion performance

Ship drag and self-propulsion simulations of a twin-screw high-speed displacement vessel were performed using the unsteady Reynolds-averaged Navier–Stokes (RANS) method. The sliding mesh and overset mesh methods were applied concurrently to simulate the coupling of the propeller rotation and the ship motion. The effects of the propeller shaft brackets on the drag, propulsion performance, wake field, and propeller excitation force were studied. The influence of the shaft brackets on the wake field was visualized. The high numerical accuracy of the proposed simulation method was proven through verification and validation analyses. The low-speed zones of nominal wake within the propeller disc were mainly caused by vortex shedding from the vicinity of the shaft brackets and the speed reduction of the frictional wake resulting from the velocity stagnation in front of the rudder. The tangential wake velocity, which was affected by the twist angle and vortex shedding, had a considerable effect on the propulsion performance. The wake non-uniformity coefficient was highly correlated with the vortex shedding. The spatial structure of the shaft bracket and the inward curved streamline around the stern aggravated the non-uniformity further, but the shaft bracket had a limited impact on the unsteady propeller bearing force in the absence of cavitation.