Flow field structure and coupled motion characteristics of forward shock waves induced by rotating detonation under axial incoming flow conditions

To reveal the coupled motion characteristics of the forward shock wave and rotating detonation wave in an air-breathing rotating detonation engine, this study combines theoretical derivation with three-dimensional non-premixed numerical simulation. It investigates the flow field structure and coupled motion characteristics of the rotating detonation-induced forward shock wave within the operating ranges of injection equivalence ratio 0.4–0.8 and axial incoming flow temperature 487–909 K, while analyzing the factors influencing the motion of the forward shock wave and the coupling laws of the wave system. Theoretical analysis shows that the axial propagation velocity of the forward shock wave is proportional to the incoming flow temperature and the forward shock wave pressure ratio, and inversely proportional to the incoming flow Mach number; its circumferential velocity is consistent with that of the rotating detonation wave due to the traction of the rotating detonation wave. Numerical results indicate that the forward shock wave interacts with the supersonic incoming flow to form a boundary-type trailing shock wave, and a complex coupled wave system structure of trailing shock wave-forward shock wave-rotating detonation wave exists from the isolator to the combustor. The fill region inside the combustor exhibits stratified mixing and a segmented shock structure. Under conditions of high equivalence ratio (φ=0.8) or low incoming flow temperature (487 K), the forward shock wave features a high pressure ratio and propagation velocity, leading to its ejection from the isolator. Under conditions of low equivalence ratio (φ=0.6) or high incoming flow temperature (909 K), the forward shock wave pressure ratio and velocity decrease, confining the forward shock wave within the isolator; additionally, high incoming flow temperature enhances mixing, resulting in the suppression of the forward shock wave in the form of a trailing shock train. Adjustments to air temperature and equivalence ratio affect the propagation characteristics (wave velocity, wave angle, and core region position) of the rotating detonation wave by altering the stratified structure of the fill region, and ultimately influence the propagation and suppression of the forward shock wave through changes in the axial velocity of the flow field. The propagation velocity, angle, and pressure ratio of the forward shock wave decrease significantly with reduced equivalence ratio or increased incoming flow temperature, and the forward shock wave transitions from being ejected from the isolator to being suppressed within it. This reveals the key influence mechanism of equivalence ratio and incoming flow temperature on the propagation of the forward shock wave and the status of the isolator. Furthermore, a simplified two-dimensional wave system model is established to analyze the formation, motion compression, and suppression laws of the forward shock wave.