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Holmboe wave fields in simulation and experiment

Published online by Cambridge University Press:  07 April 2010

J. R. CARPENTER ,
E. W. TEDFORD ,
M. RAHMANI  and
G. A. LAWRENCE
J. R. CARPENTER*
Affiliation:
Department of Civil Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
E. W. TEDFORD
Affiliation:
Department of Civil Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
M. RAHMANI
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
*
†Present address: EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Seestrasse 79, Kastanienbaum, Switzerland. Email address for correspondence: jeffcarp@gmail.com
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Abstract

The basic wave field resulting from Holmboe's instability is studied both numerically and experimentally. Comparisons between the direct numerical simulations (DNS) and laboratory experiments result in Holmboe waves that are similar in their appearance and phase speed. However, different boundary conditions result in mean flows that display gradual variations either temporally (in the simulations) or spatially (in the experiments). These differences are found to affect the evolution of the dominant wavenumber and amplitude of the wave field. The simulations exhibit a nonlinear ‘wave coarsening’ effect, whereby the energy is shifted to lower wavenumbers in discrete merging events. This process is typically found to result from either ejections of mixed fluid away from the density interface or vortex pairing. In the experiments, energy is transferred to lower wavenumbers by the ‘stretching’ of the wave field by a gradually varying mean velocity. This stretching results in a reduction of wave amplitude compared with the DNS.

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Papers
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Journal of Fluid Mechanics , Volume 648 , 10 April 2010 , pp. 205 - 223
Copyright
Copyright © Cambridge University Press 2010

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