Advectional enhancement of eddy diffusivity under parametric disorder

TL;DR

This paper investigates how parametric disorder and weak advection can significantly enhance eddy diffusivity in a fluid layer, combining numerical and analytical methods to reveal the underlying mechanisms.

Contribution

It introduces a combined numerical and analytical study of advection's role in delocalizing convective currents and boosting effective diffusivity in disordered fluid systems.

Findings

Weak advection causes drastic increase in effective diffusivity.

Parametric disorder leads to localized convective currents affecting scalar transport.

Analytical models confirm numerical observations of diffusivity enhancement.

Abstract

Frozen parametric disorder can lead to appearance of sets of localized convective currents in an otherwise stable (quiescent) fluid layer heated from below. These currents significantly influence the transport of an admixture (or any other passive scalar) along the layer. When the molecular diffusivity of the admixture is small in comparison to the thermal one, which is quite typical in nature, disorder can enhance the effective (eddy) diffusivity by several orders of magnitude in comparison to the molecular diffusivity. In this paper we study the effect of an imposed longitudinal advection on delocalization of convective currents, both numerically and analytically; and report subsequent drastic boost of the effective diffusivity for weak advection.