Two- and three-dimensional effects in the supersonic mixing layer

Experimental results are presented that compare the structure of the turbulent, planar mixing layer for three values of convective Mach number (0.28, 0.62, and 0.79), which span the range from low to moderate compressibility. Extensive planar laser Mie scattering visualizations are presented, where either mixed fluid or highspeed fluid is marked. The visualizations show that the supersonic mixing layer, when driven to low convective Mach number, behaves as an incompressible layer with characteristic two-dimensional, organized, BrownRoshko structure. As convective Mach number increases, however, the mixing layer becomes highly three dimensional, with little apparent two-dimensional, large-scale organization. This change in structure is a compressibility effect and is not a Reynolds number effect.