On Geometrical Alignment Properties of Two-Dimensional Forced Turbulence

In the present work we investigate the physical mechanisms which underlie the formation and evolution of the enstrophy cascade in two-dimensional (2D) forced turbulence. Following the work [1], it is argued that analysis of vorticity gradient can capture important aspects of the enstrophy dynamics. An extensive discussion of the generation of strong vorticity jumps in 2D turbulence can be found in [2] (and references quoted therein). Intensity of the production of vorticity gradient depends on (i) its alignment with respect to the principal axes of strain and (ii) strain magnitude. It will be shown below that in the 2D forced turbulence vorticity gradient reveals a tendency towards alignment that results in its intensified amplification. This implies internal organization of the flow at small scales.