Near-Wake of an Inclined 6:1 Spheroid at Reynolds Number 4000

Abstract

The flow around a 6:1 prolate spheroid at 45 deg inclination angle and Reynolds number 4000 (based on the minor axis) is described. Despite the fact that the inflow is uniform and steady, the resulting wake is highly asymmetric and unsteady. Two main vortical structures develop from the shear layers of the spheroid, with one being significantly stronger than the other. This asymmetry results in a nonzero side force. The forces acting on the spheroid change dramatically from earlier works at Reynolds number 3000. The pressure inside the vortex cores also change with this moderate increase in Reynolds number. This indicates that the flow is highly transitional. It is also documented that, close to the body, on the side of the weaker vortex, there is a region of negative axial velocity. In this backflow region, fluid enters from behind the spheroid and travels forward against the inflow and then exits the backflow region through one of the main vortical structures. This backflow has not been described before. A distinct Kelvin–Helmholtz shear-layer instability close to this region is also observed and described.