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Instability and cross-boundary-layer transport by shoaling internal waves over realistic slopes

Published online by Cambridge University Press:  22 May 2020

Chengzhu Xu Open the ORCID record for Chengzhu Xu [Opens in a new window]  and
Marek Stastna
Chengzhu Xu*
Affiliation:
Department of Civil Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada
Marek Stastna
Affiliation:
Department of Applied Mathematics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
*
†Email address for correspondence: chengzhu.xu@ucalgary.ca
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Abstract

Internal solitary and solitary-like waves (ISW) play an important role in mixing and sediment resuspension in naturally occurring stratified fluids, primarily through various instabilities and wave-breaking mechanisms. When shoaling into shallow waters, waves of depression may either fission into a packet of waves of elevation over mild slopes or break over steep slopes. The fissioning process is generally considered a less efficient transport and resuspension mechanism, compared to wave breaking, since very little turbulent mixing or energy dissipation occurs during this process. In the present work, however, we found that this is not always the case, at least in the particular context of ISW boundary-layer interaction. Using high-resolution numerical simulations performed in a domain representing a tilted laboratory tank, we found that boundary-layer instability in the form of a separation bubble consistently occurs during the fissioning process. The separation bubble is generated beneath the wave of elevation that emerges from the fissioning process, and is vitally influenced by currents induced by the leading wave of depression. As the waves shoal further, the growth and breakdown of the separation bubble leads to significant cross-boundary-layer transport. The results suggest that the fissioning process, which occurs over a considerable geographical region in the ocean, can be as efficient as wave breaking when it comes to cross-boundary-layer transport.

JFM classification

Geophysical and Geological Flows: Internal waves Boundary Layers: Boundary layer separation Geophysical and Geological Flows: Sediment transport
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 895 , 25 July 2020 , R6
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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