Affiliations: Department of Power Mechanical Engineering, National
Tsing Hua University, Hsinchu, Taiwan 30043, R.O.C.
Abstract: 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 number
M_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, for M_c <0.6.