Transverse Injection from Circular and Elliptic Nozzles into a Supersonic Crossflow

An investigation of sonic transverse injection from circular and elliptic nozzles into a supersonic crossflow using planar Rayleigh/Mie scattering is reported. Instantaneous images allow examination of the structural details, whereas ensemble-averaged images provide transverse penetration and lateral spread data for each jet. Standard deviation images produce information regarding the large-scale mixing/entrainment and reveal the mixing zones. Results show a highly three-dimensional near-field interaction dominated by shear-layer eddies and a counter-rotating vortex pair. Ensemble-averaged results show that the elliptic jet spreads more rapidly in the lateral direction than the circular jet, confirming that an axis-switching phenomenon is present. Near-field transverse penetration data collapse well with low-speed scaling conventions; however, the jet produced by the elliptic nozzle suffers a 20% reduction in penetration compared to the circular jet. Compressibility level does not play a significant role in the average penetration or spread of these jets, although it strongly affects the mixing/entrainment and large-scale structure. Analysis of mixing potential from the standard deviation images indicates that the low and high convective Mach number M_c injection cases are significantly different; low M_c injection yields better large-scale mixing potential than high M_c injection regardless of the injector geometry.