Planar visualizations of large-scale turbulent structures in axisymmetric supersonic separated flows

The spatial evolution of large-scale turbulent structures in the shear laye r of an axisymmetric, supersonic separated how has been investigated. The e xperimental diagnostic used was planar visualization of condensed ethanol d roplets that were suspended in the supersonic free stream. Spatial correlat ion analyses of large ensembles of images show that the mean side-view stru cture is highly strained and elliptical in shape and is inclined toward the local free stream direction. It is also shown that the effect of lateral s treamline convergence for this axisymmetric case causes a reduction in side -view structure size and eccentricity at the reattachment point as compared to the planar case. End-view structures are wedge shaped, wider on the fre e-stream side than on the recirculation region or developing wake side. It is concluded that the wedge shape is caused by the axisymmetric confinement of the shear layer as it approaches the wake centerline. The average numbe r of structures present in the end-view plane decreases significantly from 10-14 at recompression to 4-5 in the developing wake region. Evidence of an amalgamation of end-view structures in the images at the reattachment poin t illustrates one of the mechanisms responsible for this reduction. (C) 199 9 American Institute of Physics. [S1070-6631(99)02501-5].