INSTANTANEOUS 3-DIMENSIONAL FLOW VISUALIZATION OF A SUPERSONIC MIXINGLAYER

An imaging technique capable of time-resolved, three-dimensional visua lizations of compressible flows is described and applied to a superson ic mixing layer. The three-dimensional planar imaging system uses a cu stom high-speed camera to acquire 10 successive planar images through the mixing layer at a rate of 10(7) frames per second. Mixed fluid in the layer is visualized by Mie scattering of a laser light sheet from condensed alcohol droplets. After collection, the planar images are co rrected for distortions and stacked to form data volumes. Comparative visualizations at low and moderate convective Mach numbers (M(c) = 0.4 3 and 0.62) are used to examine the effects of compressibility on larg e-scale structure in mixing layers. The visualizations graphically rev eal the shift from two-dimensional spanwise rollers to three-dimension al structure, such as oblique and V-shaped bands, with increasing comp ressibility. Additionally, direct comparison between the high- and low -speed edges of the mixing layer shows the high-speed interface to be smoother than its low speed counterpart.