On the influence of Bow region vortices on SFS2 bistable airwake

Abstract

The flow field of a full-scale simplified frigate model SFS2 is simulated numerically in ANSYS Fluent® 19.0 environment using embedded LES turbulence model. The emphasis of this manuscript is to provide insight into the influence of bow region coherent vortical structures on the characteristics of the bistable airwake impacting the hovering region of flight deck. The constructive interaction of bow leading edge vortex on starboard side with the respective lobe of horseshoe vortex, generated at foot of forward face of superstructure, is found to be responsible for so called “locking” of otherwise uniform incoming flow towards starboard side. Hence, the asymmetry or bias of the bistable airwake towards starboard side can also be explained. Spectral analyses of the velocity measurements recorded in the bow region and the superstructure airwake supplements and validates the influence of bow vortical system on the airwake, as dominant frequencies associated with these vortices are also observed in airwake spectrum. Moreover, the drag force of the SFS2 as well as the airwake dynamics are found to be influenced by the turbulent flow structures shed from the both the port and starboard sides of superstructure.