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Effects of channel geometry on buoyancy-driven mixing

Hallez, Yannick and Magnaudet, Jacques Effects of channel geometry on buoyancy-driven mixing. (2008) Physics of Fluids, vol. 20 (n° 5). pp. 1-9. ISSN 1070-6631

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Official URL: http://dx.doi.org/10.1063/1.2918379

Abstract

The evolution of the concentration and flow fields resulting from the gravitational mixing of two interpenetrating miscible fluids placed in a tilted tube or channel is studied by using direct numerical simulation. Three-dimensional (3D) geometries, including a cylindrical tube and a square channel, are considered as well as a purely two-dimensional (2D) channel. Striking differences between the 2D and 3D geometries are observed during the long-time evolution of the flow. We show that these differences are due to those existing between the 2D and 3D dynamics of the vorticity field. More precisely, in two dimensions, the strong coherence and long persistence of vortices enable them to periodically cut the channels of pure fluid that feed the front. In contrast, in 3D geometries, the weaker coherence of the vortical motions makes the segregational effect due to the transverse component of buoyancy strong enough to preserve a fluid channel near the front of each current. This results in three different regimes for the front velocity (depending on the tilt angle), which is in agreement with the results of a recent experimental investigation. The evolution of the front topology and the relation between the front velocity and the concentration jump across the front are investigated in planar and cylindrical geometries and highlight the differences between 2D and 3D mixing dynamics.

Item Type:Article
Additional Information:Thanks to American Institute of Physics editor. The definitive version is available at http://pof.aip.org/ The original PDF of the article can be found at Physics of Fluids website : http://pof.aip.org/resource/1/phfle6/v20/i5/p053306_s1
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT
Université de Toulouse > Université Paul Sabatier-Toulouse III - UPS
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Deposited By: Yannick Hallez

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