Steadiness of wave complex induced by oblique detonation wave reflection before an expansion corner

Oblique detonation wave (ODW) reflection before an expansion corner leads to a sophisticated wave complex, whose steadiness is critical to achieve a practical oblique detonation engine. Both steady and unsteady wave complexes have been observed before, but the features of unsteady wave dynamics with related unsteadiness rules are still unclear so far. In this study, the ODW reflections before an expansion corner have been simulated using the reactive Euler equations with a two-step induction–reaction kinetic model, and the wave complex structures and dynamics have been analyzed correspondingly. Three subsonic zones have been distinguished, and their interactions were found to determine the wave complex steadiness. The main subsonic zone derives from the ODW reflection, which locates behind the Mach stem, while two other subsonic zones form due to the shock reflection downstream. The two downstream subsonic zones might travel upstream and combine with the main subsonic zone, resulting in two different unsteadiness modes. These wave complex dynamics were analyzed with respect to the deflection location, deflection angle and inflow Mach number, leading to the boundaries of combustion modes and ascertaining the rule of mode regime. Some transient phenomena related with the flow instability have been also discussed, clarifying fine flow structures further.