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‘Stable’ density stratification as a catalyst for instability

Published online by Cambridge University Press:  19 April 2006

D. J. Acheson
D. J. Acheson*
Affiliation:
Jesus College, Oxford
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Abstract

A physical explanation is suggested for how the instability of certain fluid systems may be provoked by the addition of a ‘bottom-heavy’ density gradient. It is shown that in all the recent examples of this behaviour the stratification shifts the oscillation frequency at the marginal state towards the diffusion rate associated with the driving mechanism for the instability, and this allows a more effective release of the available energy. When the driving mechanism is an adverse temperature gradient, for example, the frequency shift induced by a bottom-heavy solute distribution can increase the temperature change that a vertically-displaced fluid parcel acquires during each halfcycle, thereby enhancing the thermal buoyancy forces which drive the instability.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 96 , Issue 4 , 27 February 1980 , pp. 723 - 733
Copyright
Copyright © 1980 Cambridge University Press

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