Investigation into the influence of Reynolds number on the wake features of a sail of an underwater vehicle

The nominal wake of a sail attached to an underwater vehicle can adversely affect the efficiency of the vehicle’s aft appendages and propulsion, with the horseshoe vortex (HSV) component being the largest contributor to this effect.  While previous studies have focused on the tip vortex, nearfield vortices of a foil or the wake of a submarine sail at model scale conditions, there is limited information in the public domain on the evolution of the horseshoe vortex downstream with respect to varying Reynolds number.

This paper investigates the evolution of the sail horseshoe vortex as it travels downstream at different Reynolds numbers using Reynolds Averaged Navier Stokes (RANS)-based simulations. The simulation model was validated against the Rood wing experimental data, a shape commonly used for benchmark studies of nearfield foil-body junction flows. The model was then extended to investigate the sail geometry from the BB2 generic conventional submarine geometry at model scale to full scale Reynolds numbers. The study looks at the sail mounted on a ground board (similar to the Rood wing). The sail was also extended to an ‘infinite span’ configuration to investigate the influence of the tip vortex on the evolution of the downstream horseshoe vortex. As the Reynolds number increased, the horseshoe vortex was found to increase in height with its core location shifting further away from the centreline. Additionally, the presence of the tip vortex intensifies this behaviour. These findings can inform the design and optimisation of underwater vehicle sails and help improve vehicle performance efficiency.