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 wall orie ce and a circular wall orie ce. Injection was sonic in both geometries, and the expansion ratios and mass e ow rates were matched to isolate the effects of the geometric difference. Surface oil e ow patterns were inspected to determine the extent of boundary-layer separation upstream of each injector, shadowgraphs were used to visualize the e owe elds, and probe measurements were utilized to determine local helium concentrations. The wedgeshaped injection scheme demonstrated more rapid penetration into the freestream and increased mixing when compared to the baseline circular orie ce. In addition, the oil e ow photography showed that the wedge-shaped injector had no upstream separation zone, whereas the circular injector had a large separation zone. The wedge cone guration 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.