Advance of Scramjet Operating Mode Comprehension based on Shock Tunnel Experiments and Numerical Modelling

For future hypersonic transport aircraft or space launch vehicles based on combined cycle engines, the supersonic combustion ramjet (scramjet) is a promising component of the propulsion system. In particular for atmospheric flight Mach numbers in excess of 8, shock tunnel facilities are well suited to duplicate these flight conditions. The focus of the present article is to provide a review of selected important achievements obtained in free piston driven shock tunnel facilities. Research activities conducted in laboratories around the globe will be highlighted followed by a more detailed discussion of the combined experimental and numerical work performed on hydrogen fuelled integrated scramjet configurations at the German Aerospace Center (DLR). The ground based testing was conducted in the High Enthalpy Shock Tunnel Göttingen (HEG) and the computations were performed utilizing the DLR TAU code. Among the considered configurations is the Australian HyShot II flight test vehicle. It is considered to be well suited for fundamental combustor investigations and numerical tool validation purposes. Benchmark data were compiled in HEG related to different combustor modes. These data are related to the nominal operating mode and additionally to the response of the HyShot II combustor to equivalence ratios close to the critical value at which the onset of thermal choking occurs. The detailed analysis of the developing shock train and its unexpected behaviour revealed new insight into the combustor flow generated by localized thermal choking. A small scale flight experiment was designed in the framework of the European Commission co-funded LAPCAT II project. The complete scramjet flow path was subsequently tested in HEG and the numerically predicted positive aero-propulsive balance could be demonstrated by utilizing the free flight force measurement technique based on optical tracking