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

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Lucas, D 
Caulfield, CP 
Kerswell, RR 

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 stratifica- tion 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.

Description

Keywords

bifurcation, instability, stratified turbulence

Journal Title

Journal of Fluid Mechanics

Conference Name

Journal ISSN

0022-1120
1469-7645

Volume Title

832

Publisher

Cambridge University Press (CUP)
Sponsorship
Engineering and Physical Sciences Research Council (EP/K034529/1)