Instantaneous three-dimensional flow visualization of a supersonic mixing layer

An imaging technique capable of time-resolved, three-dimensional visualizations of compressible flows is described and applied to a supersonic mixing layer. The three-dimensional planar imaging system uses a custom high-speed camera to acquire 10 successive planar images through the mixing layer at a rate of 10⁷ 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 corrected for distortions and stacked to form data volumes. Comparative visualizations at low and moderate convective Mach numbers (M_c = 0.43 and 0.62) are used to examine the effects of compressibility on large-scale structure in mixing layers. The visualizations graphically reveal the shift from two-dimensional spanwise rollers to three-dimensional structure, such as oblique and V-shaped bands, with increasing compressibility. Additionally, direct comparison between the high- and low-speed edges of the mixing layer shows the high-speed interface to be smoother than its lowspeed counterpart.The authors would like to acknowledge Dr. Michael Miller and Dr. Jerry Seitzman for many helpful discussions, and William Urban for assistance in performing the experiments. This work is supported by the Air Force Office of Scientific Research, Aerospace Sciences Directorate, J. Tishkoff technical monitor.