CFD Analysis of Unstart Characteristics of the HyShot-II Scramjet Configuration in the HEG Shock Tunnel

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. In the present article, the extension of previous numerical analyses which focused on the HyShot II design condition (equivalence ratio of approximately 0.3) to unsteady flow situations in the combustor is discussed. With increasing fuel equivalence ratio, a transition from steady to unsteady flow was observed experimentally. 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 0.6