COMPRESSIBILITY EFFECTS AND MIXING ENHANCEMENT IN TURBULENT FREE SHEAR FLOWS

Computational simulations have been performed to study compressible, s patially developing turbulent free shear layers with various velocity regimes-subsonic/subsonic, supersonic/subsonic, and supersonic/superso nic for convective Mach numbers in the range of 0.14-1.28. The numeric al code used the finite volume technique and a modified Godunov's sche me, The computed results for the supersonic/subsonic case are first co mpared with experimental axial mean-velocity profiles, vorticity thick ness, and turbulence parameters. Mixing layers with various velocity r egimes are then calculated to investigate compressibility effects on t he evolution of large-scale structures through the flow visualization of the vorticity field, growth rate of the vorticity thickness, and vo rticity dynamics analysis. Various forcing frequencies are applied at the inflow boundary to examine mixing enhancement for free shear layer s with higher convective Mach numbers. It is found for the first time that the growth rate of supersonic/supersonic free shear layers increa ses markedly when the forced layers move up and down with time instead of forming vortex roll up and pairing.