UNRAVELING THE MECHANISMS OF VORTEX SHEDDING IN SUPERSONIC WAKES PAST BLUFF BODIES

Abstract

While incompressible flow past a circular cylinder exhibits classical von Kármán vortex shedding in the wake, the fundamental mechanisms governing vortex shedding in supersonic flow remain less well understood. Insight into this flow regime is crucial for several emerging aerospace applications, including supersonic planetary entry vehicles, high-speed munitions, particle-laden flows, and supersonic parachute systems. This study employs Direct Numerical Simulation (DNS) to investigate the effects of Mach and Reynolds numbers on wake dynamics behind bluff bodies and the underlying mechanism driving the downstream vortex shedding. Results show that increasing Mach number strengthens shock structures and suppresses downstream shedding, while increasing Reynolds number promotes smaller-scale, chaotic flow features. This work identifies two key vortex shedding mechanisms. Mechanism A, partially extending prior work, involves enhanced mixing in the recirculation region that destabilizes the shear layer and generates unsteady shock oscillations. Mechanism B, introduced here as a novel contribution, describes shock–shock interactions that produce a secondary shear layer and compression wave, directly amplifying, and in some regimes, initiating vortex shedding. Finally, 2D and 3D cylinder flows are shown to exhibit surprisingly similar mean characteristics, although the critical Reynolds number is much lower in the 3D case.