Phenomenology of two-dimensional stably stratified turbulence under large-scale forcing

Abhishek Kumar, Mahendra K. Verma, Jai Sukhatme

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Abstract

In this paper, we characterise the scaling of energy spectra, and the interscale transfer of energy and enstrophy, for strongly, moderately and weakly stably stratified two-dimensional (2D) turbulence, restricted in a vertical plane, under large-scale random forcing. In the strongly stratified case, a large-scale vertically sheared horizontal flow (VSHF) coexists with small scale turbulence. The VSHF consists of internal gravity waves and the turbulent flow has a kinetic energy (KE) spectrum that follows an approximate k −3 scaling with zero KE flux and a robust positive enstrophy flux. The spectrum of the turbulent potential energy (PE) also approximately follows a k −3 power-law and its flux is directed to small scales. For moderate stratification, there is no VSHF and the KE of the turbulent flow exhibits Bolgiano–Obukhov scaling that transitions from a shallow k −11/5 form at large scales, to a steeper approximate k −3 scaling at small scales. The entire range of scales shows a strong forward enstrophy flux, and interestingly, large (small) scales show an inverse (forward) KE flux. The PE flux in this regime is directed to small scales, and the PE spectrum is characterised by an approximate k −1.64 scaling. Finally, for weak stratification, KE is transferred upscale and its spectrum closely follows a k −2.5 scaling, while PE exhibits a forward transfer and its spectrum shows an approximate k −1.6 power-law. For all stratification strengths, the total energy always flows from large to small scales and almost all the spectral indicies are well explained by accounting for the scale-dependent nature of the corresponding flux.
Original languageEnglish
Pages (from-to)219-239
Number of pages21
JournalJournal of Turbulence
Volume18
Issue number3
Early online date10 Jan 2017
DOIs
Publication statusPublished - 4 Mar 2017
Externally publishedYes

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Bibliographical note

This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Turbulence on 10/01/2017, available online: http://www.tandfonline.com/10.1080/14685248.2016.1271123

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Keywords

  • Direct numerical simulation
  • stratified turbulence

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