Numerical visualization of vortical structures in a spatially evolving turbulent compressible mixing layer

Large-eddy simulations are performed to numerically visualize the generation of streamwise vortical structures and its interaction with spanwisely rolled-up coherent vortical structure during the spatial development of a turbulent supersonic/subsonic mixing layer at convective Mach numberM _c =0.51. Time-dependent three-dimensional compressible conservation equations were solved with a subgrid-scale turbulence model. The numerical code used the finite-volume technique, which adopted alternately in temporal discretization the second-order, explicit MacCormack’s and modified Godunov’s schemes. Both transverse and spanwise perturbations were imposed initially for promoting the formation of spanwise rollers and counter-rotating streamwise vortices, respectively. Numerical visualizations are presented in terms of time-sequence isopressure surfaces and vorticity contours of spanwise and streamwise components. The results show that the spatial growth of three-dimensional vortical structures, in particular, the formation of chain-link-fence type structures, is adequately captured by the present computations. Vorticity dynamics is further analyzed, for the first time, to identify the dominant roles played by the convection effect followed by the vortex stretching effect on affecting the evolution of streamwise and spanwise vortical structures, respectively, forM _c <0.6.