On geometrical alignment properties of two-dimensional forced turbulence

In the present paper we study some geometrical properties of the small scales in 2D numerical turbulence. We analyze the alignment of the vorticity gradient with respect to the eigenvectors of the rate of strain tensor, a phenomenon related to the dynamics of the enstrophy cascade. Numerical simulations with different resolutions and dissipation models are used to show non-trivial dependence of the alignment on both the magnitude of the vorticity gradient and the Reynolds number. These findings are shown to be dynamical in origin and imply organization of the small scales in the flow. (C) 1999 Elsevier Science B.V. All rights reserved.