Normal, sonic helium injection through a wedge-shaped orifice into supersonic flow

Helium was injected normally to a Mach 3 airstream to simulate hydrogen fuel injection in a scramjet combustor. Two geometries were evaluated, a wedge-shaped wail orifice and a circular wall orifice, Injection was sonic in both geometries, and the expansion ratios and mass flow rates were matched to isolate the effects of the geometric difference. Surface oil now patterns were inspected to determine the extent of boundary-layer separation upstream of each injector, shadowgraphs were used to visualize the flowfields, and probe measurements were utilized to determine local helium concentrations, The wedge-shaped injection scheme demonstrated more rapid penetration into the freestream and increased mixing when compared to the baseline circular orifice, In addition, the oil how photography showed that the wedge-shaped injector had no upstream separation zone, whereas the circular injector had a large separation zone, The wedge configuration would therefore be expected to exhibit reduced wall heat transfer in an actual combustor, It is concluded that wedge-shaped, normal, fuel injectors should provide generally better performance than circular normal injectors in supersonic combustors.