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Evolution and mixing of asymmetric Holmboe instabilities

Published online by Cambridge University Press:  14 June 2007

J. R. CARPENTER ,
G. A. LAWRENCE  and
W. D. SMYTH
J. R. CARPENTER
Affiliation:
Department of Civil Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
G. A. LAWRENCE
Affiliation:
Department of Civil Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
W. D. SMYTH
Affiliation:
College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA
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Abstract

When a stably stratified density interface is embedded in a region of strong velocity shear, hydrodynamic instabilities result. Here we generalize the stratified shear layer to allow an offset between the centre of the shear layer and the density interface. By including this asymmetry, and keeping the density interface thin with respect to the shear layer, the asymmetric Holmboe (AH) instability emerges. This study examines the evolution and mixing behaviour of AH instabilities, and compares the results to the well-known Kelvin–Helmholtz (KH) and Holmboe instabilities. This is done by performing a series of direct numerical simulations (DNS). The simulation results show that there are two different mixing mechanisms present. The first is a feature of KH instabilities and leads to the mixing and production of intermediate density fluid. The second mixing mechanism is found in AH and Holmboe instabilities and consists of regions of mixing and turbulence production that are located on one or both sides of the density interface. Since the Holmboe-type instabilities do not generate a large-scale overturning of the central isopycnal, the density interface is able to retain its identity throughout the mixing event. The amount of mixing that takes place is found to be strongly dependent on the degree of asymmetry in the flow.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 582 , 10 July 2007 , pp. 103 - 132
Copyright
Copyright © Cambridge University Press 2007

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