Flow studies on a hydrogen-fueled cavity flame-holder scramjet

This work extends an investigation into the use of a cavity flameholder to aid scramjet combustion at high flight Mach number. A parallel scramjet duct incorporating a cavity flame holder in the floor with an inclined rear face and an aspect ratio of 4.8 was investigated. The experiments were performed in a shock tunnel facility operated in semi-direct-connect mode. Measurements of the axial pressure distribution along the floor of the duct were made and both planar laser induced fluorescence (PLIF) and luminosity images were recorded of the flow in the vicinity of the duct. The experiments described here were for a range of equivalence ratios for hydrogen injected axiaily upstream into the cavity from the rear ramp of the cavity. This paper discusses the comparison of pressure data with the luminosity Images and with steady state CFD simulations of the flow in the scramjet duct. While agreement was reasonable, especially in the form of the centerline pressure distribution down the duct, the numerical predictions under predict the observed pressure levels. This may to indicative of both the uncertainty in the free stream flow state and the simplified chemistry model used. Additionally the steady state model can not capture the inherently unsteady nature observed for the flow field. Simulations at slightly lower flight Mach number indicate that combustion at these lower conditions is only marginal. The numerical simulations Indicate that the pressure drag penalty incurred by the cavity can be reduced by the injection of fuel Into the cavity and further again by the combustion of the fuel above the cavity.