Investigation of large-scale structures in supersonic planar base flows

Time-resolved, planar imaging was employed to study the spatial organization of large-scale structures within the shear layers, at reattachment, and in the wake region of a supersonic base flow. Side and end views were obtained at several streamwise locations to characterize the evolution and three-dimensionality of the large-scale motions. From statistically significant ensembles, spatial correlation fields were computed to quantify the mean size, eccentricity, and orientation of the large structures. Visualizations confirm that large-scale turbulent structures exist at all stations in the shear layers and interact vigorously with the recirculation region. Mach and/or shock waves are frequently seen emanating from within the shear layer, which may be indicative of eddy shocklet formation. The embedded turbulent structures are elliptical in shape and usually appear inclined to the mean flow direction. A distinct flattening and tilting in the streamwise direction occur as the coherent eddies negotiate shear layer formation, recompression, and reattachment processes. Spatial statistics indicate that the structures have a streamwise and spanwise spatial extent on the order of the local shear layer thickness. Examinations of spatial correlation fields suggest that the embedded structures are thoroughly three dimensional at all streamwise stations. The structures exhibit a slightly stronger organization in the spanwise direction during the initial region of the shear layer; however, near recompression, a transition occurs in which the streamwise coherency of the structures becomes dominant. Furthermore, the structures appear to degrade in their spatial organization during the recompression and reattachment processes.