Local and Nonlocal Dispersive Turbulence
Abstract
We consider the evolution of a family of 2D dispersive turbulence models. The members of this family involve the nonlinear advection of a dynamically active scalar field, the locality of the streamfunction-scalar relation is denoted by α, with smaller α implying increased locality. The dispersive nature arises via a linear term whose strength is characterized by a parameter ε. Setting 0 < ε 1, we investigate the interplay of advection and dispersion for differing degrees of locality. Specifically, we study the forward (inverse) transfer of enstrophy (energy) under large-scale (small-scale) random forcing. Straightforward arguments suggest that for small α the scalar field should consist of progressively larger eddies, while for large α the scalar field is expected to have a filamentary structure resulting from a stretch and fold mechanism. Confirming this, we proceed to forced/dissipative dispersive numerical experiments under weakly non-local to local conditions. For ε 1, there is quantitative agreement between non-dispersive estimates and observed slopes in the inverse energy transfer regime. On the other hand, forward enstrophy transfer regime always yields slopes that are significantly steeper than the corresponding non-dispersive estimate. Additional simulations show the scaling in the inverse regime to be sensitive to the strength of the dispersive term : specifically, as ε decreases, the inertial-range shortens and we also observe that the slope of the power-law decreases. On the other hand, for the same range of ε values, the forward regime scaling is fairly universal.