Depletion of advection in turbulent scalar mixing

Abstract

In turbulent scalar mixing the mean square advection is strongly suppressed with respect to its Gaussian estimate. This effect is particularly important in the small scales and related to the scales in which diffusion plays a role. The link with the generation of passive scalar fronts is discussed and it is argued that scalar fronts are the consequence of the underlying suppression of nonlinearity observed in a wide class of flows for which the dynamics are governed by quadratic nonlinearities or pseudo-nonlinearities.