Numerical Investigation of the Effect of Blockage on the Hydrodynamic Coefficients of a Prolate Spheroid

Experiments with submarine models in cavitation tunnels are limited by the length scale of the body in relation to the size of the test section. Especially for high angles of attack, the body will experience strong flow interference due to the proximity of the walls. Consequently, the hydrodynamic coefficients will normally require empirical corrections in order to be extrapolated to represent open-water flows. The present work investigates the effect of local hydrodynamic blockage, i.e. the ratio between the body frontal area to the cross area of the test section, on the determination of the hydrodynamic coefficients of a prolate spheroid. Numerical simulations of the flow around the body in various angles of attack were performed solving the Re-averaged Navier-Stokes equations for Reynolds numbers in the range of 60 million. The numerical domain is built to represent the test section of a large cavitation tunnel in full scale. Results for coefficients of lift, drag and pitching moment are compared for several cases with blockage ratio of 0%, 1% and 5% and angle of attack of 0 and 10 degrees. The maximum deviation of around 30% from the reference case was obtained at the angle of attack of 10 degrees for the highest blockage ratio. The topology of the flow showed no significant dependency on blockage for the tested range.