Regular to Mach reflection transition in truly nonstationary flows - Influence of surface roughness

The reflection of oblique shock waves is divided into three cases according to steady, pseudosteady, and truly nonstationary flows, and the transition point from regular (RR) to Mach reflection (MR) is investigated. For RR-to-MR and MR-to-RR transitions over concave, convex, smooth and rough wedges, the surface roughness was found to increase, and the wedge angle to decrease, with the transition angle becoming independent of the incident shock wave Mach number. For a mesh 40 sandpaper surface roughness, the MR-to-RR transition occurred at 54 deg, and the RR-to-MR took place at 27 deg. The transition point from RR-to-MR is also found to differ from the point from MR-to-RR, indicating the existence of a hysteresis loop in truly nonstationary flows.