Spanwise distribution of the loads on a hydrofoil working in the wake of an upstream propeller

The spanwise distribution of the loads acting on a hydrofoil working in the wake of a propeller is analyzed both as a function of the propeller load and the incidence of the hydrofoil. The analysis is based on data from Large Eddy Simulations, conducted on cylindrical grids consisting of O(10) points. Although very large coherent structures are shed by the propeller at outer and inner radii (tip and hub vortices), the average loads on the hydrofoil are characterized by peaks correlating with the radial coordinate of maximum load of the propeller blades, equivalent to about 70% of their outer radius. The azimuthal velocity of the propeller wake causes a displacement of the stagnation point in front of the hydrofoil, affecting substantially the pressure fields on its port and starboard sides and, as a result, the loads it experiences. This flow physics suggests that twisted geometries, able to decrease the local incidence angle, can produce substantial benefits on the stresses experienced by rudders operating in the wake of upstream propellers.