Tip vortices shed by a hydrofoil in the wake of a marine propeller

Abstract

Large-eddy simulations on a grid consisting of 3.8 billion points are reported, dealing with a system composed of a propeller and a downstream semi-infinite hydrofoil, mimicking a propeller–rudder system typical of surface ships. The analysis is focused on the tip vortices shed by the hydrofoil across four values of incidence angle. The results of the simulations highlight the generation of two vortices, from the pressure and suction edges of the tip of the hydrofoil, respectively, with the former more intense than the latter. They promote higher turbulence levels and pressure fluctuations at the tip of the suction side of the hydrofoil and especially at its bottom end, while the pressure side is almost unaffected. For large incidence angles, they join in the near wake of the system into a single streamwise-oriented structure. This dominates the wake signature. It is a location of minima of pressure and maxima of turbulence, which affect performance in terms of cavitation and noise. Large levels of turbulent kinetic energy are also achieved in the region of shear of this vortex with the tip vortices shed by the propeller and coming from the pressure side of the hydrofoil, rolling around the vortex from the tip of the hydrofoil. In contrast, at no incidence or for small angles, the wake of the system is dominated by the shear layer shed from the trailing edge of the hydrofoil and by the hub and tip vortices populating the wake of the propeller.