Unsteady Three-Dimensional Separated Flows Around a Sphere - Analysis of Vortex Chain Formation

Abstract

The near-wake vortex formation process behind blunt bodies is still unclear. While experiments often provide high-resolution of the far-wake vortex flow or the wall-flow (oil-flow visualization) it is still difficult to get insight into the unsteady, threedimenisonal near-wake flow. Therefore, the aim of our analysis of a low Mach number (Ma = 0,4) numerical flow simulation around a sphere is to shed some light onto the near-wake flow region. Different types of vortices, vortex chains and vortex sheddings appear in experiments [1] for increasing Reynolds numbers. For the time being, we are limited to a 71 × 71 × 71 mesh with approximately 25 grid points for Re = 400 in wall-normal direction within the boundary layer near the point of flow separation. Since the sequence of topological changes of the various quantities defining a flow field in parameter space is not necessarily dependent on the numerical resolution (although the quantitative differences for some fixed parameters may be considerable) we can hope to identify generic features of structural flow changes despite of the numerical resolution limitations given. A review of our earlier results is given in [2].