Numerical study on effect of air throttling on combustion mode formation and transition in a dual-mode scramjet combustor

Air throttling has a great effect on combustion mode formation and transition in a dual-mode scramjet combustor. An unsteady CFD method was used to investigate this effect in the present paper. The simulation was carried out under the inflow conditions of Mach number of 2.0, static temperature of 656.5 K and static pressure of 0.125 MPa respectively. The location of air throttling was 575 mm downstream the combustor entrance. Our results indicated that the combustion mode could change from supersonic combustion to subsonic combustion with throttling air injected into the combustor. Without air throttling, the combustion flame was extinguished near the down wall of the combustor, which was corresponding to the supersonic combustion mode. With air throttling, the flame was stabilized near the down wall of the combustor, which was corresponding to the subsonic combustion mode. The mode transition was mainly effected by two parameters: the mass flux of throttling air and the throttling off time. A higher wall pressure was generated by a larger mass flux of air throttling, then the combustion mode transition was easy to be achieved. The combustion heat release was insufficient when the air throttling off time was shorter than usual.