Flow unsteadiness in the near-wake of a supersonic cylinder

High speed flow over a 2D circular cylinder produces coherent flow oscillations in the near-wake region. Previous experimental studies at free-stream Mach numbers M_∞ = 4 and 6 have identified the length of the near-wake free shear layers (S) as the relevant length scale for the oscillations. The oscillation Strouhal number, formed using S and the free-stream velocity, was found to exhibit universal behavior with respect to the Reynolds number, and the universality was also seen to hold for both M_∞ = 4 and 6. The present work aims to investigate if the universal behavior extends down to a lower supersonic Mach number. Experiments are being carried out in the Satish Dhawan Supersonic Wind Tunnel at IISc at M_∞ = 2.3, at various Reynolds numbers. The frequency of oscillations and other flow features of interest are extracted by spectral proper orthogonal decomposition (SPOD) of high-speed schlieren data. The complete experimental results along with a discussion will be presented at the meeting.