Development of the wake shed by a system composed of a propeller and a rudder at incidence

Large Eddy Simulations are reported on a system consisting of a marine propeller and a hydrofoil, mimicking a rudder, for four orientations of the latter, modeling maneuvering conditions in marine propulsion. A cylindrical grid composed of almost 4 billion points was adopted. A detailed analysis of the overall wake downstream of the system is presented, with a focus on turbulent fluctuations. They are of interest, because of their importance in affecting the acoustic signature. In the near wake the streamwise evolution of turbulent kinetic energy is rising downstream of all configurations, due to the growing shear between the wakes shed by the propeller and the hydrofoil, respectively. Increasing the incidence of the hydrofoil results in a growing complexity of the wake topology and higher levels of turbulent kinetic energy. The latter are due to the adverse pressure gradient on the suction side of the hydrofoil and especially to the shear developed between the branch of the propeller wake coming from the pressure side of the hydrofoil and the shear layer from the trailing edge of the latter. In addition, the cross-stream distribution of turbulence undergoes an increasing deviation from the anti-symmetry developed at conditions of 0° incidence, because of the different cross-stream velocities gained by the two branches of the propeller wake while moving across the pressure and suction sides of the hydrofoil.