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REVIEW ARTICLES: Geophysical Flows

Entrainment and Mixing in Stratified Flows

[+] Author and Article Information
Robert E. Breidenthal

Department of Aeronautics and Astronautics, University of Washington, Seattle WA 98195

Appl. Mech. Rev 47(6S), S108-S112 (Jun 01, 1994) doi:10.1115/1.3124383 History: Online April 29, 2009

Abstract

Entrainment, mixing, and their dependence on each other are discussed in a variety of stratified flows. In general, entrainment rates decline or are constant as the stratification is increased. The precise dependence of entrainment rate on Richardson number seems to have a variety of possible relationships. Recently, a new model has been proposed in an attempt to describe them in a unified pattern. This model introduces a new parameter, the persistence, to explain the observations. It also distinguishes between cases when the vorticity impinges on the interface from when the vorticity is already there. Surprisingly, mixing seems to be have no effect on stratified entrainment for many of these regimes. However, under some conditions the molecular mixing plays a central role in the flow. This is clear in the limit of large Richardson number, where molecular diffusion controls the rate at which mass or heat crosses a stratified interface. An even more dramatic case, similar to combustion, is mixing-induced buoyancy reversal. There even the global motions are controlled by molecular-scale mixing.

Copyright © 1994 by American Society of Mechanical Engineers
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