Mixing in scramjet combustor having upstream and downstream cavities with hydrogen fuel injection in between

This study investigates the effect of quadruple cavities on the performance of a scramjet combustor using computational methods. The investigation focuses on a two-dimensional, supersonic, non-reacting flow field simulated using Menter’s SST k -ω turbulence model to solve the Reynolds-Averaged Navier-Stokes (RANS) equations. It evaluates the impact of upstream and downstream cavities and varying fuel-to-airstream pressure ratios (FAPR) on the flow structures within the combustor, and quantifies the performance through mixing efficiency (MxE), total pressure recovery (TPR), and mass-averaged Mach number (MAMN). The combustor geometry consists of a rectangular chamber with finite-width inlets for parallel air inflow along with two rearward-facing steps. The configuration features quadruple trapezoidal cavities, with two pairs of trapezoidal cavities of aspect ratio 7 positioned on both the upstream and downstream sides of the rectangular slot fuel injector. The impacts of these cavities are thoroughly examined under varying fuel delivery pressures (FDP), and the performance of quadruple trapezoidal cavity configuration is subsequently compared to the previously studied dual trapezoidal cavity design. The insight physics of mixing in various regions of the combustor are analyzed through shockwaves and streamlines, and the performance parameters are quantified for further understanding of supersonic flow fields. Shock-to-shear layer interactions (SSLIs) and shock-to-boundary layer interactions (SBLIs) contribute crucially to the mixing process within the studied combustor, adding complexity to the flow field analysis. The maximum mixing performance obtained at the outlet of the quadruple trapezoidal cavity configured combustion chamber is 83% for FAPR 4.5. The findings reveal that the quadruple cavity configuration offers significantly improved mixing efficiency compared to the dual cavity setup, albeit at the cost of greater pressure loss. By presenting quantified outcomes and a comparison with prior research, this research provides valuable implications for advancing cavity-enhanced mixing in scramjet systems.