Influence of Heat Capacity Ratio on Pressure and Nozzle Flow of Scramjets

Kurzfassung

An experimental study of flows over a single expansion ramp nozzle with side walls was carried out at the German Aerospace Center (DLR). The tests were performed at a free-stream Mach number of 7 in the hypersonic wind tunnel H2K of the wind tunnel department in Cologne. The Reynolds number, nozzle pressure ratio, and the heat capacity ratio were varied in order to study the performance of the scramjet nozzle at different flight altitudes and run conditions. The effects of different heat capacity ratios have been investigated by using gases with higher and lower heat capacity ratios than air. The static pressure distribution on the single expansion ramp was measured by using PSI (Pressure System Incorporated) pressure transducer taps location at discrete points on the surface. Schlieren photographs were taken by a high-speed camera in order to visualize the flow field and investigate the influence of the heat capacity ratio on the interactions between the external and the nozzle flow. The obtained experimental results are discussed and compared with the Schlieren photographs. An effect of the heat capacity ratio on the pressure distribution and the interactions between external and nozzle flow was found. The data obtained by the different measurement techniques permitted a characterization of the nozzle flow and gave an insight into the properties of single expansion ramp nozzle flows.