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SUMMARY:Multi-scale state-space dynamics of near-wall turbulence - Yongyun
  Hwang (Imperial College London)
DTSTART:20220330T093000Z
DTEND:20220330T100000Z
UID:TALK171182@talks.cam.ac.uk
DESCRIPTION:Over the past decade\, there has been a significant amount of 
 evidence that coherent structures in wall-bounded shear flows emerge in th
 e form of a hierarchy (or a fractal)\, as was hypothesized by Townsend (i.
 e. attached eddy hypothesis) in 1950s. In this talk\, a numerical experime
 nt\, designed to simulate only two scale dynamics (i.e. large and small)\,
  will be introduced\, and I will present three newly discovered scale inte
 raction dynamics: 1) non-equilibrium energy cascade modulated by self-sust
 aining process\; 2) enhanced small-scale turbulence production driven by e
 nergy cascade of large scale\; 3) energy feeding from small to large scale
 . 28 invariant solutions are subsequently computed for this system\, and t
 hey are classified into 1) large scale state\; 2) small scale state\; 3) s
 cale interaction state. An exhaust examination with many physical relevant
  state-space visualisations revealed that none of the invariant solutions 
 appear near the chaotic turbulent state\, suggesting that the notion of th
 e state space from the dynamical systems theory may not be very useful for
  multi-scale turbulence. Instead\, each of the solutions is found to repre
 sent only part of the multi-scale processes. I will conclude this talk by 
 addressing how we tackle this challenge in the dynamical systems descripti
 on of turbulence.
LOCATION:Seminar Room 1\, Newton Institute
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