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Interaction between an inclined gravity current and a pycnocline in a two-layer stratification

Published online by Cambridge University Press:  21 January 2020

Yukinobu Tanimoto Open the ORCID record for Yukinobu Tanimoto [Opens in a new window] ,
Nicholas T. Ouellette Open the ORCID record for Nicholas T. Ouellette [Opens in a new window]  and
Jeffrey R. Koseff Open the ORCID record for Jeffrey R. Koseff [Opens in a new window]
Yukinobu Tanimoto*
Affiliation:
The Bob and Norma Street Environmental Fluid Mechanics Laboratory, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA94305-4020, USA
Nicholas T. Ouellette
Affiliation:
The Bob and Norma Street Environmental Fluid Mechanics Laboratory, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA94305-4020, USA
Jeffrey R. Koseff
Affiliation:
The Bob and Norma Street Environmental Fluid Mechanics Laboratory, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA94305-4020, USA
*
†Email address for correspondence: [email protected]
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Abstract

A series of laboratory experiments were conducted to investigate the characteristics of a dense gravity current flowing down an inclined slope into a quiescent two-layer stratification. The presence of the pycnocline causes the gravity current to split and intrude into the ambient at two distinct levels of neutral buoyancy, as opposed to the classical description of gravity currents in stratified media as being either a pure underflow or interflow. The splitting behaviour is observed to be dependent on the Richardson number ($Ri_{\unicode[STIX]{x1D70C}}$) of the gravity current, formulated as the ratio of the excess density and the ambient stratification. For low $Ri_{\unicode[STIX]{x1D70C}}$, underflow is more dominant, while at higher $Ri_{\unicode[STIX]{x1D70C}}$ interflow is more dominant. As $Ri_{\unicode[STIX]{x1D70C}}$ increases, however, we find that the splitting behaviour eventually becomes independent of $Ri_{\unicode[STIX]{x1D70C}}$. Additionally, we have also identified two different types of waves that form on the pycnocline in response to the intrusion of the gravity current. An underflow-dominated regime causes a pycnocline displacement where the speed of the wave crest is locked to the gravity current, whereas an interflow-dominated regime launches an internal wave that moves much faster than the gravity current head or interfacial intrusion.

JFM classification

Geophysical and Geological Flows: Gravity currents Geophysical and Geological Flows: Internal waves
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 887 , 25 March 2020 , A8
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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