DNS Study on the Evolution of Vortical Packets and Their Interactions in Boundary Layer

Vortical structures like the Λ-vortex and ring-like vortex play a critical role in the boundary layer transition process. In this paper, the mechanisms of the formation of the vortical packets and their mutual interactions are studied by DNS. It is found that the shear layer instability is the key of the vortex generation. On the other hand, in the process of evolution of vortical packets, the vortical structures(including vortex tubes and other kind of rotation cores) will continue to create high shear layers in the boundary layer by both sweeps and ejections. The generation and evolution process of the first ring-like vortex structure is studied in detail. I