RR-MR transition in curved shock wave reflections

In shock wave reflections, a transition occurs between two reflection types -- regular reflection (RR) and Mach reflection (MR) -- as the flow deflection angle is varied. Experimentally, this transition is commonly induced by varying the angle-of-attack of the shock wave generator. While RR-MR transitions have been extensively studied for planar oblique shock waves, such transitions for curved shock waves have received much lesser attention in the literature. The present work investigates RR-MR transition in a curved shock wave that reflects off a flat surface. Wind tunnel experiments were performed at a free-stream Mach number of 6, with a 2D curved compression ramp as the shock wave generator. The ramp curvature was designed to yield a constant pressure gradient along the compression surface for a Mach 6 inviscid flow at zero angle-of-attack. Schlieren imaging with high temporal resolution allows for detailed visualization of RR-MR transitions as the ramp angle-of-attack is varied continually during experiments. It was observed that the overall flow deflection angle corresponding to the transition point for the curved ramp at Mach 6 was 51.7°, which is significantly higher than the value of 37.8° reported in the literature for planar ramps.