End effects in the wake of a hydrofoil working downstream of a propeller

Abstract

Large-eddy simulations are reported on a system consisting of a marine propeller and a downstream, semi-infinite hydrofoil, carried out on a cylindrical grid of about 3.8 × 109 points. The results are compared with those of an earlier study, considering a similar hydrofoil of infinite spanwise extent, to shed light on the influence of the end effects on the wake flow. The comparisons show good agreement between the two cases at conditions of no incidence of the hydrofoil. However, as its incidence angle grows, end effects become important. Accounting for the limited spanwise extent of the hydrofoil results in the generation of a couple of streamwise-oriented vortices from the port and starboard edges of its tip, a reduced spanwise elongation of the propeller wake, and lower turbulent stresses on the suction side of the hydrofoil, where the massive separation phenomena characterizing the infinite hydrofoil at large incidence angles are missing. In the wake of the overall system, the peak values of turbulent stresses are produced in the region of shear between the vortex shed from the pressure side edge of the tip of the hydrofoil and the tip vortices from the propeller. The latter vortices roll around the former, resulting in an intense interaction between them. In contrast, downstream of the infinite hydrofoil, the highest turbulent stresses are achieved within its wake, due to its shear with the elongated wake of the propeller.