Layer formation in horizontally forced stratified turbulence: Connecting exact coherent structures to linear instabilities

Dan Lucas*, Colm-cille P Caulfield, Richard Kerswell

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

12 Citations (Scopus)
270 Downloads (Pure)

Abstract

We consider turbulence in a stratified 'Kolmogorov' flow, driven by horizontal shear in the form of sinusoidal body forcing in the presence of an imposed background linear stable stratification in the third direction. This flow configuration allows the controlled investigation of the formation of coherent structures, which here organise the flow into horizontal layers by inclining the background shear as the strength of the stratification is increased. By numerically converging exact steady states from direct numerical simulations of chaotic flow, we show, for the first time, a robust connection between linear theory predicting instabilities from infinitesimal perturbations to the robust finite-amplitude nonlinear layered state observed in the turbulence. We investigate how the observed vertical length scales are related to the primary linear instabilities and compare to previously considered examples of shear instability leading to layer formation in other horizontally sheared flows.

Original languageEnglish
Pages (from-to)409-437
Number of pages29
JournalJournal of Fluid Mechanics
Volume832
Early online date26 Oct 2017
DOIs
Publication statusPublished - 10 Dec 2017

Keywords

  • bifurcation
  • instability
  • stratified turbulence

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