A new method for isolating turbulent states in transitional stratified plane Couette flow

John Taylor, Enrico Deusebio, Colm Caulfield , Richard R Kerswell

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Abstract

We present a new adaptive control strategy to isolate and stabilize turbulent states in transitional, stably stratified plane Couette flow in which the gravitational acceleration (non-dimensionalized as the bulk Richardson number (Formula presented.)) is adjusted in time to maintain the turbulent kinetic energy (TKE) of the flow. We demonstrate that applying this method at various stages of decaying stratified turbulence halts the decay process and allows a succession of intermediate turbulent states of decreasing energy to be isolated and stabilized. Once the energy of the initial flow becomes small enough, we identify a single minimal turbulent spot, and lower-energy states decay to laminar flow. Interestingly, the turbulent states which emerge from this process have very similar time-averaged (Formula presented.), but TKE levels different by an order of magnitude. The more energetic states consist of several turbulent spots, each qualitatively similar to the minimal turbulent spot. This suggests that the minimal turbulent spot may well be the lowest-energy turbulent state which forms a basic building block of stratified plane Couette flow. The fact that a minimal spot of turbulence can be stabilized, so that it neither decays nor grows, opens up exciting opportunities for further study of spatiotemporally intermittent stratified turbulence.
Original languageEnglish
Article numberR1
Number of pages13
JournalJournal of Fluid Mechanics
Volume808
Early online date26 Oct 2016
DOIs
Publication statusPublished - Dec 2016

Keywords

  • stratified flows
  • stratified turbulence
  • transition to turbulence

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