Numerical investigation of a Mach 12 REST scramjet at off-design conditions

The description of combustion in high-speed turbulent flows where turbulent mixing, compressibility effects and chemical kinetics processes are competing, still remains a challenging issue for numerical simulations. The key features of such turbulent supersonic reactive flows are highlighted and integrated into a new Turbulence-Chemistry Interaction (TCI) closure which relies on the partially stirred reactor (PaSR) framework. The corresponding closure, hereafter denoted UPaSR model, is integrated into the Onera CFD (Computational Fluid Dynamics) code CEDRE. A Mach 12 REST (Rectangular-to-Elliptical-Shape-Transition) scramjet engine developed and tested at the University of Queensland is retained as a validation test case. Results of Reynolds Average Navier Stokes (RANS) numerical simulations based on the UPaSR concept and the QL (Quasi-Laminar) closure are presented and compared. Similar results in terms of pressure distributions were obtained. This confirmed that the essential point to cope with such scramjet engine conditions is to represent satisfactorilly the compressible flowfield. Two different strategies to evaluate the scramjet engine performance have been applied: the first one is based on a quasi-one-dimensional tool using experimental pressure distributions and the second one is based on RANS numerical simulations through the calculation of energetic efficiencies. The inlet injection scheme presented the best performance with a combustion efficiency of 78%