Circular and elliptical transverse injection into a supersonic crossflow-- the role of large-scale structures

An examination of the large-scale structure of the flowfields associated with sonic transverse injection through circular and elliptical nozzles into a Mach 2 crossflow is reported. Instantaneous shadowgraph photos provide documentation of the flowfields. Planar Rayleigh scattering images of near-field flow planes produce substantial information about the jeUcrossflow interaction. Instantaneous images allow examination of the structural details, while ensemble-averaged images provide transverse penetration and lateral spread data for each injector. Standard deviation images produce information regarding the large-scale mixing and document the development of mixing zones associated with these flows. Results show a highly three-dimensional interaction dominated in the near-field by two types of large-scale vortical motions: shear layer eddies and a counter-rotating vortex pair. Substantial differences in the shear layer structure occur when using air or helium as the injectant gas. Penetration results show that the elliptical jet spreads more quickly in the lateral direction than the circular jet, confirming that some axis-switching phenomenon is present. Near-field transverse penetration data collapse well with low speed scaling conventions, and the power law curve fits obtained are in good agreement with previous results. Finally, analysis of mixing potential from the standard deviation images indicates that the helium and air injection flowfields show significant differences that suggest air injection yields better large-scale mixing potential than helium injection.