Study on the transition patterns of the oblique detonation wave with varying temperature of the hydrogen-air mixture

•It is found that the smooth and abrupt transition patterns do exist at high and low Mach numbers.•The transition pattern is understood based on flame propagation.•The competition between the detonation velocity and the inflow velocity dominates the transition patterns. The Oblique Detonation Wave Engine is among the promising choices for hypersonic propulsion systems. It is of great importance to investigate the initiation of the oblique detonation wave. Although it has been demonstrated that there exist two transition patterns from oblique shock wave to oblique detonation wave, i.e., abrupt and smooth, the key parameter that dominates the transition is not clear. A study on the transition patterns of the oblique detonation wave in hydrogen-air mixture with varying temperature is conducted. The oblique detonation wave angle is measured to calculate the detonation velocity. It is found that the effects of the inflow temperature on the detonation velocity are negligible when compared with the effects on the inflow velocity, which means that the inflow velocity dominates the transition patterns when changing the temperature of the mixture. Both smooth and abrupt transitions can exist for a given Mach number by changing the mixture temperature. It is further proved that what determines the smooth and abrupt transitions is the angle difference between the oblique detonation wave and the oblique shock wave (ODW-OSW). Due to a fact that the propagation velocity of a flame front equals to the normal component of the inflow velocity when the flame is stationary, the competition between the detonation velocity and the inflow velocity dominates the ODW angle. Thus, the competition between the detonation velocity and the inflow velocity can act as a criterion for transition patterns.