Identification of Large Structures in Compressible Mixing Layers using Filtered Rayleigh Scattering

Abstract

High Reynolds number compressible planar free shear layers were investigated using a visualization technique based on filtered Rayleigh/Mie scattering. Two convective Mach numbers, Mc=0.51 and 0.86, were studied in the developing and fully developed regions. Scattering was collected from condensed water particles; both product formation and passive scalar methods were utilized. A molecular filter was used to eliminate the background scattering from walls and windows. The large structures in the Mc=0.51 case appear as nominally two-dimensional spanwise rollers possessing relatively well defined core and braid regions, and experience amalgamation and tearing processes similar to those observed in incompressible free shear layers. The Mc=0.51 plan and spanwise views indicate the presence of organized streamwise vortices in both the developing and fully developed regions. The structures for the Mc=0.86 case are much less organized than the Mc=0.51 case and highly three dimensional. There is no clear evidence of streamwise vortices for this case. However, the large structures seem to typically be spanwise oblique in the fully developed region.