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On convection and mixing driven bysedimentation

Published online by Cambridge University Press:  26 April 2006

Silvana S. S. Cardoso  and
Andrew W. Woods
Silvana S. S. Cardoso
Affiliation:
Institute of Theoretical Geophysics, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge CB3 9EW, UK
Andrew W. Woods
Affiliation:
Institute of Theoretical Geophysics, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Silver Street, Cambridge CB3 9EW, UK
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Abstract

The sedimentation of small particles from a suspension and theconcomitant release of light interstitial fluid may constitute abuoyancy source for the development of convective motions. When thedense suspension is emplaced beneath a stratified fluid anintermediate convecting layer between the sedimenting front and thedensity gradient above gradually grows in depth by erosion of theoverlying stratified fluid. Novel laboratory experiments involvingsedimentation below a two-layer stratified region show thatturbulent mixing and entrainment across the top density interface issignificant for a broad range of the Richardson number. A simpletheoretical model predicting the rate of erosion of thestratification above the convecting layer agrees well with theseexperiments. The model is then extended to include the case of anoverlying continuous density gradient and compared successfully withboth new experimental data and the original data of Kerr (1991).Owing to the effects of dispersion of grain sizes, small particlesin the convecting fluid may lower the efficiency of the interfacialmixing by the turbulent eddies.

Our model calculations suggest that turbulent mixing and entrainmentdriven by sedimentation may be significant in the atmospheric andoceanic contexts, in both of which stratification is weak. Suchmixing may also occur in molten magma chambers following thesedimentation of suspended crystals, and in this case it maysuppress large-scale overturning events.

Information

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 285 , 25 February 1995 , pp. 165 - 180
Copyright
© 1995 Cambridge University Press

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