Numerical Study of Variable Density Effects on a Spatially Developing Supersonic Turbulent Shear Layer

Direct Numerical Simulations of a spatially developing supersonic turbulent shear layer have been conducted for different density Atwood numbers to examine the combined effects of compressibility and multi-fluid global density variation on the shear layer growth rate, turbulence statistics, self-similarity, and flow asymmetry. The self-similar region of the simulated shear layer is identified by the convergence of normalized streamwise velocity and density profiles, constant peak of Reynolds stress components, and linear growth rate of momentum thickness and shear layer thickness. Introducing global density variation in the multi-fluid flow enhances the layer asymmetry as compared to the single-fluid shear layer, meaning that the shear layer centerline and peak of Reynolds stresses shift more towards the lighter fluid side. Apart from enhanced asymmetry, the increase in global density variation or the ratio of freestream fluid densities causes more reduction in shear layer growth rate. Comparative study of the effects of compressibility and global density change on flow variables like mean density or cross-stream velocity reveals some of the interesting features of the simulated compressible multi-fluid shear layer. Despite significant differences in lower and higher order statistics at different density Atwood numbers, the mean flow profiles collapse within the self-similar zone using our suggested self-similar scaling.