The three-dimensional flow organization past a micro-ramp in a supersonic boundary layer

Abstract

The three-dimensional instantaneous flow organization in the near wake of a micro-ramp interacting with a Mach 2.0 supersonic turbulent boundary layer is studied using tomographic particle image velocimetry. The mean flow reveals a wake with approximately circular cross section dominated by a pair of counter-rotating streamwise vortices generating a focused upwash motion at the symmetry plane. In the instantaneous flow organization a flow instability of Kelvin-Helmholtz (K-H) type is observed in the shear layer between the wake and outer flow. Intermittent arc-shaped vortices are visualized that locally accelerate the outer fluid and further decelerate the inner region. The streamwise vortex pair displays an undulating behavior. Their interaction with the K-H vortices considerably increases the overall complexity of the wake. It appears that the streamwise vortex filaments under the K-H vortex train approach each other due to the focused ejection activity resulting from the K-H vortex. The statistical properties of turbulent fluctuations yield maximum activity at the core of the streamwise vortex and within the upwash region, and the Reynolds stresses peak within the shear layer. The topological organization of the wake vortices is formulated through a conditional average over the vorticity field.