Document Type

Article

Publication Date

2-2009

Journal or Book Title

Journal of Fluid Mechanics

Volume

621

First Page

1

Last Page

21

DOI

10.1017/S0022112008004308

Abstract

Scalars with different molecular diffusivities can be transported at different rates in a strongly stratified, weakly turbulent flow. Rapid distortion theory (RDT) is used to examine the mechanisms responsible for differential diffusion of scalars in a sheared stratified flow. The theory, which applies when the flow is strongly stratified, predicts upgradient flux and its wavenumber dependence, which previous direct numerical simulations have shown to be important in differential diffusion. The net effect of shear on differential diffusion depends on the Grashof number, or the relative importance of buoyancy and viscous effects. RDT also allows the effects of the density ratio, Schmidt number, Lewis number, scalar activity and mean shear to be examined without the high computational cost of direct numerical simulation. RDT predicts that differential diffusion will increase with increasing density ratio, but only at low Grashof number. When the Lewis number is fixed, the Grashof number below which differential diffusion occurs decreases with increasing Schmidt number, and when one of the Schmidt numbers is fixed, differential diffusion decreases with increasing Lewis number. Also, differential transport of passive scalars increases when the Schmidt number of the scalar stratifying the flow increases.

Research Focus Area

Environmental/Water Resources Engineering

Comments

This article is from Journal of Fluid Mechanics 621 (2009): 1–21, doi:10.1017/S0022112008004308. Posted with permission.

Copyright Owner

Cambridge University Press

Language

en

File Format

application/pdf

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