LES study of the interaction of a propeller with a downstream hydrofoil at incidence

Results of Large-Eddy Simulations on a system composed of a propeller and a downstream hydrofoil at four angles of incidence are reported. Computations were conducted on a cylindrical grid consisting of about 4 billion points. Results of first- and second-order statistics of the propeller performance and forces on the hydrofoil are reported. The latter are also correlated with the fluctuations of pressure within the boundary layer, showing that increasing the incidence angle results in larger values on both its pressure and suction sides, especially in the regions of impingement by the tip and hub vortices shed by the propeller. Also the development of the near wake is discussed, with a particular focus on turbulent kinetic energy, due to its role in affecting the acoustic signature of the overall system. Larger angles of incidence increase the levels of turbulence. This is due to (i) the stronger instabilities developing within the boundary layer over the suction side of the hydrofoil and (ii) the more intense shear between the wakes shed by the propeller and the hydrofoil, respectively, as a result of the more significant cross-stream velocities developed by the flow. The latter source of turbulence was found dominating the development of the near wake, resulting for all cases of incidence in a growing streamwise evolution of turbulent kinetic energy, reinforcing the signature of the propeller-rudder system at downstream locations.