Visualization on Supersonic Flow over 2D Backward Facing Step with Control

The fine flow structures over a backward facing step (BFS) under Mach 3.4 were studied experimentally. The experiments were carried out as three states:without control, with roughness and with micro-vortex generator (MVG) control to the upstream flow of BFS. The streamwise and spanwise flow images with high spatial-temporal resolution were captured via nano-tracer based planar laser scattering (NPLS) technique and the surface static pressures were measured using micro-electric pressure scanning valve. Based on the large number of instantaneous flow images, the time-averaged flow was investigated. From contrasts among the flow structures at different times, the characteristic time of the large scale turbulent structures was claimed out. With roughness control, the pressure in the recirculation flow region is lower than that without control, while the pressure downstream is larger. With MVG control, the pressure around the step increases in a very short distance. MVG will change the flow state strongly than other types and the roughness can adjust the flow around the step to be transited with few differences.