An experimental investigation of large-scale structures in supersonic reattaching shear 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. Single-pulse 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. Double-pulse visualizations were also performed to capture an accurate time history of individual structures and to measure the local streamwise convection velocity.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 layers 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 occurs 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. Furthermore, the structures appear to degrade in their spatial organization during the recompression and reattachment processes.Time-correlated images indicate that the individual structures evolve primarily through an elongation and rotation toward the streamwise direction. The structures possess a limited temporal coherence, typically of the order of one eddy roll-over time. Convection velocities near the base are higher than the isentropic prediction, in agreement with previous compressible shear layer studies. During recompression and reattachment, the structures slow considerably, apparently in response to the adverse pressure gradient. Downstream of reattachment, the structures accelerate as the mean flow accelerates.U of I OnlyETDs are only available to UIUC Users without author permissio