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Salt finger fluxes in a laminar shear flow

Published online by Cambridge University Press:  28 June 2010

ALEXANDRE M. FERNANDES  and
R. KRISHNAMURTI
ALEXANDRE M. FERNANDES*
Affiliation:
Department of Oceanography and Geophysical Fluid Dynamics Institute, Florida State University, Tallahassee, FL 32306, USA Departamento de Oceanografia Física, Universidade do Estado do Rio de Janeiro, R. São Francisco Xavier, 524, Sala 4017E, Rio de Janeiro, RJ 20550-900, Brazil
R. KRISHNAMURTI
Affiliation:
Department of Oceanography and Geophysical Fluid Dynamics Institute, Florida State University, Tallahassee, FL 32306, USA
*
†Email address for correspondence: alexmf@gfdi.fsu.edu
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Abstract

Subtropical ocean waters are susceptible to the occurrence of salt finger instability. The effect of salt fingers in modifying water mass properties may depend upon the ubiquitous presence of oceanic shear produced by internal wave motion. We present an experimental study of the buoyancy fluxes produced by sugar–salt fingers in the presence of a laminar shear flow. As is commonly done in the laboratory, sugar (the slower diffuser) was used as a proxy for salt, and salt (the faster diffuser compared to sugar) was used as a proxy for cold. Sugar–salt fingers, initially aligned vertically, were observed to tilt when a shear flow was imposed. A consistent decrease in the salt fluxes was measured as the Reynolds number (Re) was increased by increasing the shear velocity magnitude. Through regression analysis, the salt fluxes were found to depend upon the Reynolds number as Re−0.025, Re−0.1 and Re−0.34, for density ratio values (Rρ) equal to 1.2, 1.54 and 2.1 respectively. The salt fluxes produced by the sheared fingers were also found to decrease by one order of magnitude when Rρ increased from 1.2 to 2.1. A computation of the salt Nusselt number revealed that the finger fluxes approach molecular flux values when Rρ = 2.1 and Re ≃ 140.

JFM classification

Low-Reynolds-number flows: Low-Reynolds-number flows Flow Control: Mixing enhancement
Type
Papers
Information
Journal of Fluid Mechanics , Volume 658 , 10 September 2010 , pp. 148 - 165
Copyright
Copyright © Cambridge University Press 2010

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