Flow structure in the near wake of an axisymmetric supersonic base flow using tomographic PIV

The flow field following separation from a blunt-faced cylindrical body aligned with a supersonic freestream is highly unsteady and turbulent. Although the governing geometry of the flow field is simple, there are complex, three-dimensional flow structures that dominate the near wake. The recompression wake region of this flow field is studied here via non-timecorrelated tomographic particle image velocimetry (tomo-PIV) measurements. A large ensemble of three-component, volumetric, instantaneous velocity measurements was acquired to present an appropriately converged mean flow field by which to compare the unsteadiness of the instantaneous measurements. Coherent vortex identification methodologies, such as the Q-criterion, the swirling strength criterion, and the vorticity magnitude were utilized to display the measured flow structures. In this measurement region, canonical turbulent structures are identified, including symmetric hairpin vortices and asymmetric hairpins (i.e., cane-shaped vortices). Comparisons with numerical studies are drawn as to the shape, size, and number density of these coherent flow structures.