Near wake of a propeller across a hydrofoil at incidence

Large-eddy simulations of a propeller operating upstream of a hydrofoil at incidence were conducted on a cylindrical grid consisting of almost 4 × 109 points. This manuscript, focused on the interaction between the tip and hub vortices shed by the propeller with the downstream hydrofoil, is part of a broader study, including the analysis of the boundary layer on the hydrofoil [A. Posa and R. Broglia, "Flow over a hydrofoil at incidence immersed within the wake of a propeller,"Phys. Fluids 33, 125108 (2021)] and the downstream development of the wake of the overall system [A. Posa and R. Broglia, "Development of the wake shed by a system composed of a propeller and a rudder at incidence,"Int. J. Heat Fluid Flow 94, 108919 (2022)]. The results demonstrate a substantial influence by the orientation of the hydrofoil on the propeller wake. The pressure and suction side branches of the tip vortices experience outward and inward spanwise shifts across the hydrofoil, respectively. However, these shifts are affected significantly by the angle of incidence. As a result, the propeller wake undergoes an overall contraction on the suction side of the hydrofoil, promoting higher levels of shear and turbulence and a faster growth of the boundary layer thickness. The opposite occurs on the pressure side of the hydrofoil, producing eventually a strong asymmetry of the overall wake. Also the evolution of the hub vortex is substantially affected. It splits into two branches, shifting across the span of the hydrofoil in the direction opposite to the tip vortices. As the incidence angle of the hydrofoil grows, the branch of the hub vortex populating its pressure side becomes larger than the one on its suction side, developing a higher shear with the hydrofoil boundary layer and the suction side branches of the tip vortices.