The spatial evolution of large scale structures in supersonic shear layers with the convective Mach number range from Mc=0.2 to Mc=8 are simulated with a Discontinuous Galerkin code in the current study, to look into the function of large scale structures on the growth rate of shear layers. Special attention is paid on the process of the evolution of large scale structures from up to down streams. The simulation results are compared with flow visualization with a planar laser Mie scattering(PLMS) technique are carried with Mc=0.107 and Mc=0.474. It is found that the scale of structures is larger in higher Mc case, and the merging, interaction process of large scale structures in higher Mc case is slower as that of lower Mc case, which is partially answer the decreasing of growth rate of shear layers with increasing Mc, namely the compressibility. As the Mc going on, shocklets structures appear, which are differrent from cases of lower Mc. In three dimensional cases, cases of Mc=0.4 and Mc=0.8 are investigated, The λ2structure extraction method is utilized in this paper, the "forest" structures are evident.
