Equivalent direct connect free-stream shock tunnel conditions for injection locations in an axisymmetric scramjet

Fuel injection optimisation into radical farming scramjets is one of the key technologies being developed at the University of Queensland [18, 6, 13]. To facilitate the experimental testing of some these injection techniques, equivalent tunnel free-stream conditions at the injection locations had to be determined. To compare against previous work [19, 3] and intended flight test data [20] the free-stream conditions were calculated relative to the intended 48 kPa constant dynamic pressure trajectory of the SCRAMSPACE vehicle [4]. Due to the variation of the equivalent standard atmosphere through the test period (33-27 km [20]) and the discreet nature of the nozzles available on the tunnel, the constraining variable used to calculate the conditions was not the flight enthalpy but the ramp injection Mach number; which is the reverse to the standard procedure [10, 15]. By constraining the nozzle exit Mach number, the equivalent flight enthalpy could be determined from the projected flight dynamic pressure and reverse calculating the inviscid conical shocks of the truncated Busemann inlet. Using this equivalent flight enthalpy, a multi-dimensional Kriging based surrogate model was developed to give a surface response to the equivalent tunnel conditions of flows produced in the T4 Hypersonic Shock Tunnel. The final calculated conditions are estimated to be tuned but not necessarily tailored due to the constant compression ratios used in the facility [9]