The hydrodynamic interaction of turbulent flow with tandem hydrofoils in presence of a free surface

Hydrofoils are essential element in order to design marine propulsion system, hydrokinetics turbines and many more practical engineering applications. So, the evaluation of hydrodynamic performance of hydrofoils in different arrangements is very important. In the present study, the hydrodynamic performance of a NACA 0012 hydrofoils in tandem in close proximity of a free surface is studied in the turbulent flow field. Vorticity distribution, velocity contour of the hydrofoils for a large range of angles of attack are numerically investigated at the Reynolds number of 166784.8 and at a Froude number of 0.57. Further, the interaction of vortex ring at the free surfaces with hydrofoils arranged in tandem are investigated. The unsteady flow dynamics around the tandem hydrofoil is computed with a particular emphasis on the determining the effect of angle of attack on the vorticity generated at the free surface. The governing incompressible unsteady Navier-Stokes equations for turbulence flow over the tandem foil system were modeled in a finite volume framework using SIMPLE algorithm for pressure-velocity coupling in star CCM+ commercial CFD package. The free-surface is captured using the volume of fluid (VOF) method while the flow turbulence is modelled using the k- method. Further, the grid independence study is carried out in order to optimize the grid resolution for the computationally effective simulation in the present work. The obtained results are validated with the available experimental results of Duncan (1983). The present study establishes the significant effects on the vorticity at the free surface due to the change in angle of attack and spacing distance of hydrofoils in tandem arrangements.