Experimental investigation of a two-dimensional and a three-dimensional scramjet inlet at Mach 7

The current experimental study at Mach 7 was carried out to investigate the viscous How effects in a scramjet inlet with a fixed geometry operating at Mach 7.5-8. To reduce the risk of inlet unstart, an optional passive boundary-layer bleed was integrated at the throat and tested for different bleed dimensions. The passive bleed significantly reduces the lip-shock-induced separation bubble on the ramp. But the correct location of the bleed gap is important for the reduction of the separation bubble. To investigate the compression behavior, different backpressures were applied and the effects on the internal flow structure were analyzed by means of static pressure along the isolator and pilot pressure profiles at the exit of the isolator. Because the reference configuration has a very small internal contraction ratio to guarantee self-starting, the internal compression ratio was increased in three steps by means or additional sidewall compression along the internal flowpath. This includes internal contraction ratios above the starting limit. This measure led to a significant increase of the static pressure ratio at the end of the isolator. The complex flow structures are explained by means of detailed static and pitot pressure plots.