Physical and Numerical Study of Three-Dimensional Skewed Mixing Layers

摘要

The effect of skewing the two freestreams on the development of a compressiblemixing layer was studied. The results of stability analysis show that skewing has the simultaneous effect of increasing the effective velocity ratio, which is a destabilizing effect, and increasing the effective, convective Mach number, which is a stabilizing effect. Direct numerical simulations of a spatially evolving mixing layer with equal velocity magnitude but skewed in opposite directions were conducted to study the non-linear evolution. Three skewing angles were considered: 30, 60, and 90 deg. For the low skewing angle cases, the mixing layer rolls up and forms a pattern of streamwise vortices. For the 90 deg case, vortex breakdown was observed, which significantly enhances the mixing. Results of stability analysis show that adding a small amount of swirl near the center of the mixing layer significantly enhances the maximum amplification rate, and the enhancement sustains under compressible conditions. The disturbance energy budget shows that a significant of disturbance energy is extracted from the shear in the swirl component.