Interaction between strain and vorticity in compressible turbulent boundary layer

The interaction of strain and vorticity in compressible turbulent boundary layers at Mach number 2.0 and 4.9 is studied by direct numerical simulation (DNS) of the compressible Navier-Stokes equations. Some fundamental characteristics have been studied for both the enstrophy producing and destroying regions. It is found that large enstrophy production is associated with high dissipation and high enstrophy, while large enstrophy destruction with moderate ones. The enstrophy production and destruction are also correlated with the dissipation production and destruction. Moreover, the enstrophy producing region has a distinct tendency to be 'sheet-like' structures and the enstrophy destroying region tends to be 'tube-like' in the inner layer. Correspondingly, the tendency to be 'sheet-like' or 'tube-like' structures is no longer obvious in the outer layer. Further, the alignment between the vorticity vector and the strain-rate eigenvector is analyzed in the flow topologies. It is noticed that the enstrophy production rate depends mainly on the alignment between the vorticity vector and the intermediate eigenvector in the inner layer, and the enstrophy production (destruction) mainly on the alignment between the vorticity vector and the extensive (compressive) eigenvector in the outer layer.