Study on the flow field structure and mixing characteristics in dual injection schemes of scramjet combustor

This study investigated the impact of various dual injection schemes on the flow field structure and mixing characteristics in scramjet combustor. Experiments were conducted using a directly connected experimental setup, with the total temperature of the high-speed incoming flow generated by the heater being 1650K and the total pressure being 1.3 MPa. The combustion chamber inlet Mach number is 2.52, and the global equivalence ratio for ethylene is 0.4, covering four fuel injection configurations. According to numerical and experimental results, the primary jet generates two sets of counter-rotating vortex pairs (CVP1 and CVPA), which merge before the secondary jet forms additional vortices (CVP2, CVPB, and CVP). These vortices converge in the central region of the cavity, forming a dominant vortex that influences mixing in the far field. Compared to single injection, dual injection enhances mixing by increasing recirculation zones and vorticity between the primary and secondary jets, resulting in a 27% increase in mixing efficiency within the cavity. As the distance between the jets increases from 7D (D = 3 mm) to 14D, the interaction between recirculation zones R3 and R4 weakens, leading to a 11.4% reduction in the penetration depth of the secondary jet and a 20% decrease in mixing efficiency. When the distance between the fuel and the cavity’s leading edge is reduced from 14D to 7D, the interaction between the downstream jet and the cavity is enhanced. However, the reduced penetration depth constrains fuel distribution, making it difficult to achieve sufficient mixing over a shorter distance. As a result, a longer mixing path is required for effective combustion, leading to a 23.8% decrease in overall mixing efficiency.