Simulation of high mach number scramjet flow conditions using the X2 expansion tube

Expansion tubes are the only type of ground test facility currently able to simulate high Mach number scramjet test ows. These access-to-space ow conditions are characterised by total pressures of the order of gigapascals. The University of Queensland's X2 expansion tube facility has recently been used to generate scramjet ow conditions between Mach 10-14, with total pressures up to 10 GPa. Flow conditions were relevant to a 96 kPa dynamic pressure ascent trajectory. For ground testing of sub-scale scramjet-powered vehicles, pressure-length (p-L) scaling is used in order to maintain similarity for various ight parameters, such as Reynolds number, total enthalpy, and binary reaction rates. X2 was congured to achieve test ow static pressures considerably higher than the true ight values, while maintaining true ight velocities and temperatures, thereby demonstrating signicant potential for p-L scaling, which is typically necessary since most model scramjet engines need to be tested at sub-scale. This paper details the combined analytical and numerical process used to develop new ow conditions in X2. Experimental results are presented for four new ow conditions, and axisymmetric CFD analysis is used to fully characterise test ow properties