Large structure convection velocity measurements in compressible transverse injection flowfields

An examination of the convection characteristics of the large-scale structures developing in flowfields created by sonic transverse injection through circular and elliptical nozzles into a Mach 1.98 crossfiow is reported. Temporally correlated Rayleigh/Mie scattering images taken at the spanwise centerline of the jet/freestream interaction illustrate the characteristics of the highly intermittent structures residing at the interface and allow determination of both the structure convection velocity and structure convection angle. Results indicate that, for a given jet-tofreestream momentum flux ratio, both injector geometry and compressibility play significant roles in influencing the convection characteristics of the large eddies. High compressibility injection cases have dramatically larger near-field convection velocities than their low compressibility counterparts. Farther downstream, as the jet plume bends due to the oncoming freestream flow, the large-scale vortices tend to travel at velocities nearer the freestream velocity. Injector geometry primarily affects the near-field behavior with the elliptical nozzle producing shallower convection angles and convection velocities that are skewed toward the velocity of the freestream. Apparently, the axis-switching phenomenon and the weaker bow shock associated with the elliptical nozzle geometry influence the structural development, resulting in the documented trends.