Effect of Compressibility on Supersonic Cylinder Wakes: Insights from Time Accurate Numerical Simulations

Supersonic bluff-body wakes exhibit complex unsteady behavior that remains poorly understood. This study investigates (1) the influence of Mach number on supersonic bluff-body wake features and (2) the physical mechanism driving downstream vortex shedding. Direct numerical simulations of flow over a two-dimensional cylinder at Mach 1.2–5 and a freestream Reynolds number of 200,000 are performed. The results show that increasing Mach number strengthens shock structures, confines the wake, and progressively damps vortical features. It also intensifies a Type-VI Edney shock–shock interaction occurring in the downstream wake. SPOD and PSD analysis reveal that convective instabilities propagate through the separated shear layers, eventually developing into high-frequency Kelvin–Helmholtz shedding downstream. Visualizations of the unsteady flow field further show that the recirculation region is highly dynamic at low supersonic Mach numbers and introduces perturbations into the separated shear layers, which may contribute to initiating these instabilities.