Flow splitting in numerical simulations of oceanic dense-water outflows

Gustavo M. Marques, Mathew G. Wells, Laurie Padman, Tamay M Ozgokmen

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5  m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B0=Q0N3/g′2 (where Q0 is the volume flux of the dense water flow per unit width, N is the ambient stratification and g′ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B0 ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B0 ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B0 ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr < 1). This transition is associated with an internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

Original languageEnglish (US)
Pages (from-to)66-84
Number of pages19
JournalOcean Modelling
Volume113
DOIs
StatePublished - May 1 2017

Fingerprint

dense water
Gravitation
outflow
Transition flow
Computer simulation
simulation
Water
Hydraulic jump
Froude number
gravity
Experiments
Prandtl number
Buoyancy
stratification
Lakes
Boussinesq equation
Fluxes
gravity flow
buoyancy
water flow

Keywords

  • Gravity currents
  • Intermediate and bottom water formation
  • Internal hydraulic jump
  • Overflows

ASJC Scopus subject areas

  • Oceanography
  • Computer Science (miscellaneous)
  • Geotechnical Engineering and Engineering Geology
  • Atmospheric Science

Cite this

Flow splitting in numerical simulations of oceanic dense-water outflows. / Marques, Gustavo M.; Wells, Mathew G.; Padman, Laurie; Ozgokmen, Tamay M.

In: Ocean Modelling, Vol. 113, 01.05.2017, p. 66-84.

Research output: Contribution to journalArticle

Marques, Gustavo M. ; Wells, Mathew G. ; Padman, Laurie ; Ozgokmen, Tamay M. / Flow splitting in numerical simulations of oceanic dense-water outflows. In: Ocean Modelling. 2017 ; Vol. 113. pp. 66-84.
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