The response of a continuously stratified fluid to an oscillating flow past an obstacle

TitleThe response of a continuously stratified fluid to an oscillating flow past an obstacle
Publication TypeJournal Article
Year of Publication2013
AuthorsWinters KB, Armi L.
JournalJournal of Fluid Mechanics
Volume727
Pagination83-118
Date Published2013/07
Type of ArticleArticle
ISBN Number0022-1120
Accession NumberWOS:000321576600007
Keywordsconversion; diffusion; hydraulic control; internal waves; internal-tide generation; model; ocean; ridge; supercritical topography; topographic effects; waves
Abstract

An oscillating continuously stratified flow past an isolated obstacle is investigated using scaling arguments and two-dimensional non-hydrostatic numerical experiments. A new dynamic scaling is introduced that incorporates the blocking of fluid with insufficient energy to overcome the background stratification and crest the obstacle. This clarifies the distinction between linear and nonlinear flow regimes near the crest of the obstacle. The flow is decomposed into propagating and non-propagating components. In the linear limit, the non-propagating component is related to the unstratified potential flow past the obstacle and the radiating component exhibits narrow wave beams that are tangent to the obstacle at critical points. When the flow is nonlinear, the near crest flow oscillates between states that include asymmetric, crest-controlled flows. Thin, fast, supercritical layers plunge in the lee, separate from the obstacle and undergo shear instability in the fluid interior. These flow features are localized to the neighbourhood of the crest where the flow transitions from subcriticality to supercriticality and are non-propagating. The nonlinear excitation of energetic non-propagating components reduces the efficiency of topographic radiation in comparison with linear dynamics.

DOI10.1017/jfm.2013.247
Short TitleJ. Fluid Mech.
Integrated Research Themes: 
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