Large Eddy Simulation for Compressible Plane Free Shear Layers Transition Process

In this paper, three types of 3-D spatial evolving compressible plane shear layers, namely, supersonic/supersonic mixing layers, supersonic/subsonic mixing layers and subsonic/subsonic mixing layers, are studied. The transition process and fully developed turbulent flows in different convective Mach numbers are investigated using the large eddy simulation (LES) method based three-dimensional compressible Favre-filtered Navier-Stokes equations. Paper emphasizes to investigate the unsteady characteristic including mechanism of instability, inherent structures and statistics parameters of turbulence and reliability Analysis of computational results by theory and experiment data. Based on the linear stability theory, a pair of the most unstable oblique first mode disturbances and spontaneous perturbation is imposed on the inflow boundary. The computational results show that The most instable disturbance mechanism Induced by 2-D wave perturbation in low convective Mach number (Mc 0.6) and Λ vortices dominate the transition process. The consistency of LES results to natural transition and the relevant literature data indicates that is reasonable to investigate free shear layer development by induce linear disturbance. At the same time, flow parameters analysis indicates that momentum thickness saturation position can be seen as the sign of transition finish. Otherwise, Shocklets which distribute unsymmetrical have been captured by the LES method at the convective Mach number 1.0. Their shapes are consistent with experiment results. In the fully developed turbulence region, velocity pulse tendency towards isotropy and the compressibility effect increases with the convective Mach number elevation. These results present that LES can simulation translation mechanism of mixing layers well.