Influence of the slip length on the fluid dynamics of a marine propeller

Large Eddy Simulation (LES) was adopted to study the influence of the slip length of the surface of a marine propeller on its performance, the flow on its blades, and its wake in open water conditions. Computations were carried out on a cylindrical grid consisting of 6.7 × 109 points. The results of the simulations show a small reduction (within a few percent) of both thrust and torque, even with large values of the slip length, resulting in negligible effects on the overall efficiency of propulsion. The major effect was a slight delay in the transition to turbulence on the pressure side of the blades and an increase in the turbulent fluctuations in the vicinity of the trailing edge for larger slip lengths. The overall result of these phenomena was a rise in the unsteady component of the loads on the propeller. The wake flow was practically unchanged in terms of both topology and intensity of its major structures and the first and second order statistics. In conclusion, the results of the present study indicate only minor changes in the performance and wake features from the implementation of hydrophobic treatments or coatings on the surface of propellers, even when large values of the slip length are achieved at model-scale Reynolds numbers, which emphasize the effects of the hydrophobic properties of the surface. Although these results refer to a particular propeller and working condition, their root causes suggest they could be extended to different geometries and loads.