CFD Analysis of Unsteady Combustion Phenomena in the HyShot-II Scramjet Configuration

Abstract

Ground based testing of the generic HyShot II scramjet configuration was carried out in the High Enthalpy Shock Tunnel Göttingen, HEG, of the German Aerospace Center, DLR, and computational fluid dynamics (CFD) was applied to support the analysis of the experimental results. Previous numerical analysis was mainly focused on the steady-state design conditions at an equivalence ratio of approximately 0.3. Preliminary computations at large equivalence ratios showed that a change in flow topology corresponding to a transition from supersonic to subsonic combustion occurs. The formation of a subsonic combustion zone is seen to lead to the upstream propagation of an unsteady shock train. This phenomenon is also observed in experimental investigations. In the framework of scramjet engine design it is of particular interest to identify and to correctly predict the limiting operating conditions, e.g., engine unstart. Therfore, in conjunction with the test campaign performed in HEG, a parametric CFD study was performed utilizing the DLR TAU code to investigate the onset of unsteady combustor flow. Unsteady Reynolds averaged Navier-Stokes (URANS) computations were performed for off-design equivalence ratios above 0.5.