A Computational Assessment of Free Surface and Mount Effects in Towing Tank Experiments on Flow Over a 6:1 Prolate Spheroid

Pre-test simulations were performed of the high Reynolds number 6:1 prolate spheroid towing tank experiments to be carried out by the Office of Naval Research. The two Reynolds numbers of interest in the experiments were investigated, Re = 11.74e6 and Re = 1.47e6, with the prolate spheroid inclined 0°, 10°, 20°, and 45° with respect to the incoming flow. Reynolds-Averaged Navier-Stokes simulations were conducted for three flow configurations. The first included a 6:1 prolate spheroid mounted to a sting and strut under a free surface. The second configuration removed the mounting geometry, and the last configuration omitted the mounting geometry and the free surface. Increments in the forces and moments acting on the prolate spheroid were calculated to quantify the impact of the free surface and mounting geometry on the force measurements in the towing tank experiments. The addition of the free surface resulted in relatively small increments except for the side force at 45° incidence. Increments in the forces and moments due to the addition of the strut were generally larger, particularly at high incidence angles, and reached up to 5% of the total values.