Abstract: Based on Large-eddy simulation，combined with the high order hybrid schemes，the three-dimensional spatially-developing supersonic planar mixing layer at two density ratios s=1.0 and 0.138) were investigated numerically for Mac=1.1. The numerical results illustrate clearly the evolution of supersonic mixing layer under the effect of perturbation，and the structure characteristics and generation process of the shocklets in three-dimensional mixing layer are discussed. In addition，the effects of different density ratio of the upper and lower sides of the mixing layer on the instability of the mixing layer and the generation of the shocklets were analyzed，and found that the instability of mixing layer can be accelerated as the density of the both sides unequal，and the intensity of shocklets decreases as well. Moreover，the shocklet intensity in lower density layer is weaker.

Key words: Supersonic mixing layer；Shocklets；Variable-density flow；Large-eddy simulation

摘要： 基于大涡模拟方法与高精度混合格式，对两种密度比(1.0与0.138)条件下的高对流马赫数(Mac=1.1)三维空间发展超声速平面混合层进行了数值模拟。数值结果清晰描述了扰动激励下超声速平面混合层的演变过程，讨论了三维混合层中小激波的结构及其形成过程。分析了混合层两侧密度变化对混合层失稳及小激波形成的影响，发现当上、下层密度不等时，混合层失稳加速，小激波强度减弱，而密度较低侧的小激波会更弱。

关键词: 超声速混合层；小激波；变密度流；大涡模拟