Vorticity gradient stretching in the direct enstrophy transfer process of two-dimensional turbulence

Abstract

In two-dimensional turbulence enstrophy is injected at the forcing scale and transferred down to the dissipative scale where viscosity dominates. On intermediate scales the forward enstrophy cascade is accompanied by a stretching of the vorticity gradient (VG) at the strain rate (SR), resulting in a preferential orthogonality between the VG and the stretching direction. In a coordinate system formed by the SR eigenvectors at a fixed time, we find that the VG statistically turns toward the direction perpendicular to the eigenvector corresponding to the stretching, as shown in the figure.