Experimental Investigation of RR-MR Transition in Curved Shock Wave Reflections

The transition between regular reflections (RR) and Mach reflections (MR) of shock waves has pertinence in the design of supersonic and hypersonic air intakes. Traditionally, RR-MR transitions in steady supersonic flows have been studied with planar shock waves, mostly motivated by planar compression ramp systems. In recent years, research interest in curved compression ramp geometries has grown due to the promise of improved compression efficiency over their flat counterparts. The leading-edge ramp shock wave along the external compression surface would be curved in such intake designs. The present work focuses on understanding the mechanics of RR-MR transitions in reflections of curved shock waves off a flat surface, a scenario that is typically found in shock-wave systems that form in air intakes. Curved shock wave reflections off a flat plate were studied experimentally at Mach 6 in the Roddam Narasimha Hypersonic Wind Tunnel (RNHWT) at IISc. Wedge angle variation induced hysteresis associated with the interaction between the incident curved shock and the separation shock (generated over the plate) was found to be absent. It was observed that the overall flow deflection angle corresponding to the transition point for a curved ramp was significantly higher than the value reported in the literature for planar ramps.