Unsteady Oblique Detonation Waves in a Tunnel Induced by Inflow Mach Number Variation

Oblique detonation waves (ODWs) have been investigated widely aiming at facilitating their application in hypersonic engines. However, there is a lack of research on unsteady ODWs which are unavoidable in the hypersonic air-breathing scenario. In this study, unsteady ODWs triggered by the variation of the inflow Mach number (M₀) have been studied and the geometric model is a tunnel with an outward-deflection upper wall to mimic an engine outlet. Numerical results demonstrate that when M₀ deviates from the designed state, two typical wave structures arise, featuring a Mach stem of detonation or a post-corner recirculation zone. A sudden change in M₀ leads to the transition of these two structures, generating unsteady ODWs temporally with a multi-segment-complex wave surface caused by triple points. The wave structures near the corner have been analyzed in detail, revealing how the Mach stem and the recirculation zone evolve into each other. Furthermore, the effects of unsteady ODWs on hypersonic propulsion applications have been discussed, providing possible ways to suppress the Mach stem of detonation.