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

TitleThe turbulent transition of a supercritical downslope flow: sensitivity to downstream conditions
Publication TypeJournal Article
Year of Publication2016
AuthorsWinters KB
JournalJournal of Fluid Mechanics
Volume792
Pagination997-1012
Date Published2016/04
Type of ArticleArticle
ISBN Number0022-1120
Accession NumberWOS:000379218400007
Keywordshydraulic control; stratified flows; topographic effects
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.

DOI10.1017/jfm.2016.113
Short TitleJ. Fluid Mech.
Student Publication: 
No
Research Topics: