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The turbulent transition of a supercritical downslope flow: sensitivity to downstream conditions

Published online by Cambridge University Press:  08 March 2016

Kraig B. Winters
Kraig B. Winters*
Affiliation:
Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
*
†Email address for correspondence: kraig@coast.ucsd.edu
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Abstract

Blocked, continuously stratified, crest-controlled flows have hydraulically supercritical downslope flow in the lee of a ridge-like obstacle. The downslope flow separates from the obstacle and, depending on conditions further downstream, transitions to a subcritical state. A controlled, stratified overflow and its transition to a subcritical state are investigated here in a set of three-dimensional numerical experiments in which the height of a second, downstream ridge is varied. The downslope flow is associated with an isopycnal and streamline bifurcation, which acts to form a nearly-uniform-density isolating layer and a sharp pycnocline that separates deeper blocked and stratified fluid between the ridges from the flow above. The height of the downstream obstacle is communicated upstream via gravity waves that propagate along the density interface and set the separation depth of the downslope flow. The penetration depth of the downslope flow, its susceptibility to shear instabilities, and the amount of energy dissipated in the turbulent outflow all increase as the height of a downstream ridge, which effectively sets the downstream boundary conditions, is reduced.

JFM classification

Geophysical and Geological Flows: Hydraulic control Geophysical and Geological Flows: Stratified flows Geophysical and Geological Flows: Topographic effects
Type
Papers
Information
Journal of Fluid Mechanics , Volume 792 , 10 April 2016 , pp. 997 - 1012
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Copyright
© 2016 Cambridge University Press 

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Winters supplementary movie

Animation of the isopycnals at $x=0$ for the case $\Delta=0.84$ shown in figure 3. The contour increment is uniform and the inflowing isopycnals are colored.

Download Winters supplementary movie(Video)
Video 50.8 MB

Winters supplementary movie

Animation of the isopycnals at $x=0$ for the case $\Delta=0.84$ shown in figure 3. The contour increment is uniform and the inflowing isopycnals are colored.

Download Winters supplementary movie(Video)
Video 15 MB

Winters supplementary movie

Animation of the normalized speed $v/U_{\rm max}$ at $x=0$ for the case $\Delta=0.84$ shown in figure 3.

Download Winters supplementary movie(Video)
Video 8.5 MB

Winters supplementary movie

Animation of the normalized speed $v/U_{\rm max}$ at $x=0$ for the case $\Delta=0.84$ shown in figure 3.

Download Winters supplementary movie(Video)
Video 3.4 MB