Cylinder wake in a supersonic flow

Here, the instantaneous wake structure behind a cylinder exposed to a supersonic freestream at Mach 3 was investigated experimentally. The experiments were conducted in a supersonic blow down tunnel at the Princeton University Gas Dynamics Laboratory. Cylinders ranging in size from 6 mm OD to 40 mm OD were each held in place between two quartz windows, acting as the walls of the 48.8 x 70 x 194 mm test section. The resulting wakes were examined under various freestream conditions. A wide range of Reynolds numbers were studied, from $4 \times 10^4 to $3 \times 10^6$, based on cylinder diameter and freestream conditions.  Specifically, the periodic oscillations of the wake slipline, as reported in a previous study at Mach 4 by Schmidt & Shepherd (J. Fluid Mech., vol. 785, R3) is quantified using high-speed Schlieren and Shadowgraph. Results related to the oscillation Strouhal number will be presented and compared with the scaling proposed by Schmidt & Shepherd.