The investigation of inclined aft wall cavities in a circular scramjet combustor

Achieving good mixing with high combustion efficiency, stable flame holding, and low stagnation pressure losses are still open issues in supersonic reacting flows. Mixing and vorticity in supersonic flows are mainly driven by the baroclinic term that is correlated to the density and pressure gradients. An increase of the baroclinic term has been observed to strongly depend on shock waves arising within the combustion chamber. This work numerically investigated the interaction between the fuel jet and the air stream as a function of the aft wall angle inclination. In fact, this parameter has a primary impact on the shock wave inclination arising from the cavity leading edge and therefore on the baroclinic term. Four different combustor geometries have been investigated: without cavity and with three different aft wall inclinations (90°–15°, 60°–15°, 30°–15°). 3D RANS numerical simulations showed that the primary ramp angle has a critical impact on the fuel-air mixing and consequently on the combustion efficiency. A correlation between the combustor geometry and the shock angle inclination has been proposed. Greater combustion efficiency, homogeneous H2O, and temperature distribution across the combustor are found with the 30–15 aft wall cavity configuration. Lowering the primary aft wall of the cavity from 90° to 30°, resulted in the rising of a stronger bow shock, extended recirculation volume within the cavity, and increased fuel-air mixing.