Orateur
Description
Joint work with Julie Meunier.
The Kraichnan-Leith-Batchelor inverse energy cascade is a hallmark of 2D
turbulence. Based on such phenomenology, the effective diffusivity of a 2D
turbulent flow is dimensionally controlled by the energy flux and the
large-scale friction coefficient only. Surprisingly, however, we show that
such scaling predictions are invalidated by numerical solutions of the 2D
Navier-Stokes equation forced at small wavenumber and damped by weak linear
or quadratic drag. We derive alternate scaling-laws for the effective
diffusivity based on the emergence of intense, isolated vortices causing
spatially inhomogeneous frictional dissipation localized within the small
vortex cores. The predictions quantitatively match DNS data. This study
points to a universal large-scale organization of 2D turbulent flows in
physical space, bridging standard 2D Navier-Stokes turbulence with
large-scale geophysical turbulence.