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The dynamics of confined extensional flows

Published online by Cambridge University Press:  31 August 2016

Samuel S. Pegler
Samuel S. Pegler*
Affiliation:
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
*
†Email address for correspondence: [email protected]
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Abstract

I present a theoretical and experimental study of floating viscous fluid films introduced into a channel of finite length, motivated by the flow of glacial ice shelves. The dynamics are characterized by a mixture of viscous extensional stresses, transverse shear stresses and a driving buoyancy force. A theory based on a width-integrated model is developed and investigated using analytical, asymptotic and numerical methods. With fluid introduced at a constant rate, the flow is found to approach a steady state with two possible asymptotic forms depending on the length of the channel. For channel lengths less than half the width, the flow is similar to a purely extensional one-dimensional flow, characterized by concave surface profiles and being insensitive to the position of the channel exit (or calving front). Greater lengths result in a more complex asymptotic structure in which the flow adjusts over a short distance towards a prevailing flow of universal dimensionless form. In complete contrast to the extensional regime, the prevailing flow is controlled by the position of the channel exit. Data from a new laboratory experiment involving particle velocimetry of a floating fluid film compares well with the predicted along-channel velocity. Motivated by glaciological application, the analysis is generalized to power-law rheologies and the results used to classify the flow regimes of a selection of ice shelves. The prediction for the frontal speed is in good agreement with geophysical data, indicating that the universal profile predicted by the theory is common in nature.

JFM classification

Waves/Free-surface Flows: Channel flow Geophysical and Geological Flows: Ice sheets Interfacial Flows (free surface): Thin films
Type
Papers
Information
Journal of Fluid Mechanics , Volume 804 , 10 October 2016 , pp. 24 - 57
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Copyright
© 2016 Cambridge University Press 

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Pegler supplementary movie

This movie illustrates the initial stages of a laboratory experiment in which glucose syrup (dyed red and seeded with particles of polyvinyl carbonate) is introduced along the surface of a dense salt solution (clear). It is sped up by a factor of 25. The movie illustrates the development of an `under-thick' input, for which the flow thickens in the vicinity of the input.

Download Pegler supplementary movie(Video)
Video 2.3 MB