3D Separations within the SCRAMSPACE I Hypersonic Flight Experiment Scramjet

Abstract

The SCRAMSPACE I Mach 8 hypersonic flight experiment scramjet has been simulated using Reynolds Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) tools at angle of attack, for fuel-on and fuel-off conditions. For the fuel-on simulations, a large 3D, asymmetric, boundary layer separation forms at the entrance to the combustion chamber. Further discrete pockets of 3D counter-rotating separation form downstream from this large separation. The large separation structure at the combustion chamber entrance is shown to expel fluid into the smaller separations, creating a complex hypersonic flowfield through the engine flowpath that couples 3D shock wave/ boundary layer interactions (SWBLI) with the combustion process. The scramjet utilizes an inlet-fuelled radical farming approach, with the fuel being injected through six porthole injectors inclined at 45-degrees to the local surface of the second conical ramp of the three cone inlet. The results from 'fuel-off' and 'reactions-off' simulations demonstrate the effect on separation zone from the fuel injection process. A 2.5-degree angle of attack limit for this scramjet engine has been imposed on the flight experiment through previous experimental work, above which engine unstart is expected to occur. We provide evidence that the 3D boundary layer separation at the combustion chamber entrance observed at 2.1-degrees angle of attack grows and merges with secondary separations within the combustion chamber at higher angles of attack. We postulate that this mechanism is responsible for setting the angle of attack limit of the scramjet.