Vortex evolution in supersonic air free diffused mixing layers

The vortex formation and evolution in a supersonic air/air free diffused plane mixing layer were investigated numerically by forcing four different harmonic disturbances without phase differences. The two-dimensional compressible Navier-Stokes equations including the diffusion effect of air components were solved by using a high accuracy finite difference method. The convective terms and transport terms were discretized by a third-order upwind compact scheme and a sixth-order symmetric compact scheme, respectively. The unsteady time marching method is a third-order compact storage explicit Runge-Kutta algorithm. Some phenomena of large-scale primary vortex growing and interacting were revealed, such as saturating, paring once and twice, and triple-vortex pairing. For low convective Mach number of Ma_c=0.3, primary vortices are fatter, but their streamwise lengths are shorter. Under the influence of air real-gas characteristics, the vortex-shocklet structure is not discovered in the case of high convective Mach number of Ma_c=0.8.