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SUMMARY:Turbulence-mean-flow interactions: lessons from local 2D turbulenc
 e - Anna Frishman\, Technion
DTSTART:20230303T160000Z
DTEND:20230303T170000Z
UID:TALK195037@talks.cam.ac.uk
CONTACT:Prof. Jerome Neufeld
DESCRIPTION:How turbulence shapes a mean flow\, and how it is altered by t
 he mean flow in return\, is a central problem in fluid mechanics. It is sh
 ared by a wide range of systems\, from pipe flow to planetary scale winds 
 and currents. Mean-flow-turbulence interactions take a special character i
 n large-scale geophysical and astrophysical flows. Often constrained by ro
 tation or stratification\, the resulting flows are effectively two-dimensi
 onal. The mean flow can then spontaneously emerge in a process of self-org
 anization\, starting from small-scale fluctuations. The underlying mechani
 sm is that of an inverse transfer of energy --- from small to large scales
 \, leading to the accumulation of energy at large scales and the establish
 ment of a system-size mean flow. A prominent example are the jets on Jupit
 er\, which are powered by small scale turbulence and have remained remarka
 bly unchanged for decades.\n\nIn this talk\, I will discuss analytical and
  numerical results for turbulence-mean-flow-interactions in idealized two-
 dimensional systems. One of the difficulties in treating turbulence-mean-f
 low interactions is the non-local nature of incompressible fluid dynamics.
  I will focus on a model where this difficulty is eliminated\, considering
  a rapidly rotating shallow layer of fluid in the limit where surface pert
 urbations become localized. This is the so-called large-scale quasi-geostr
 ophic (LQG) equation. I will show how low-order turbulent statistics are d
 etermined in this model\, and how\, depending on symmetries\, they either 
 shape the mean flow or are passively set by it. This emergent picture is c
 onsistent with previous results in two-dimensional incompressible Navier-S
 tokes\, where the dynamics is non-local\, pointing at its universality. On
  the other hand\, I will also describe the dramatic influence of the local
  dynamics in LQG: the formation of regions with depleted fluxes towards sm
 all scales and a vanishing small-scale dissipation. Finally\, I will comme
 nt on possible connections to mean-flow-turbulence interactions in three-d
 imensional flows\, emphasizing commonalities and differences.\n\nwebinar: 
 https://cassyni.com/events/Se4XRUaPhS4Pv7H9TTnptm?cb=functi
LOCATION:Webinar
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