Viscous Drag Reduction in a Scramjet Combustor with Film Cooling

Experiments have been performed on a cylindrical scramjet combustor to investigate the effect of porthole and slot injection and combustion of hydrogen on viscous drag. Fuel injectors designed to provide different slot equivalence ratios were tested at a nominal freestream Mach number of 4.4 and stagnation enthalpy of 5.9 MJ/kg in the T4 free piston shock tunnel at The University of Queensland. Each fuel injector was tested over a range of total equivalence ratios and the integrated drag force was measured using a single component stress wave force balance. Experiments were performed for combustor lengths of 220, 420 and 520 millimetres. In addition, the stagnation pressure and enthalpy of the flow were varied to investigate the effect of changes in flight altitude and velocity respectively. For each injector, the greatest reduction in viscous drag was observed at low values of the total equivalence ratio. Increasing the slot equivalence ratio resulted in slightly increased levels of drag reduction. Results for variation in combustor length agreed with expected trends. However, the uncertainty in the drag measurements made it difficult to interpret the results for variation in stagnation pressure and enthalpy.