Sensitivity of mixed subsonic-supersonic turbulent mixing layers

Numerical predictions of compressible turbulent mixing layers have been performed for convective Mach numbers up to 0.7 (M-C less than or equal to0.7), This flow is particularly challenging to compute because the mixing layer consists of one supersonic stream and one subsonic stream, resulting in a mixed hyperbolic/elliptic solution. The FLUENT (C) computational fluid dynamics code, which incorporates a renormalization group k-is an element of turbulence model and the SIMPLEC solution algorithm, was used to perform the computations. Initially, predictions were performed for several different convective Mach numbers (M-C = 0.2, 0.5, and 0.7), and the computed results (mixing layer thickness, mean velocity, and turbulence parameters) were compared with experiments to benchmark the code. Following this qualification procedure, the sensitivity of the Me = 0.7 case to disturbances was further investigated by introducing small perturbations to the boundary conditions and recomputing the mixing layer. Specifically, effects of perturbations to the secondary stream stagnation pressure and test section wall adjustment angle were investigated, It was found that the compressible mixing layer growth rate was significantly altered by small changes (<4%) in the secondary stream stagnation pressure. In addition, divergence or convergence of the test section walls of less than 3 deg resulted in appreciable changes in the streamwise pressure gradient and mixing layer development.