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SUMMARY:Structure and scaling of extremely large velocity gradients in hyd
 rodynamic turbulence. - Alain Pumir (ENS - Lyon\, Max Planck Institute for
  Dynamics and Self Organisation)
DTSTART:20220531T150000Z
DTEND:20220531T160000Z
UID:TALK174776@talks.cam.ac.uk
DESCRIPTION:Fully turbulent flows are characterized by intermittent format
 ion of very localized and intense velocity gradients\, which can be orders
  of magnitude larger than their typical value. With the help of direct num
 erical simulations of the Navier&ndash\;Stokes equations at very high reso
 lution\, we characterize such extreme events over a broad range of turbule
 nce intensities. The results suggest a power-law dependence of the propert
 ies of the extreme events as a function of the Taylor-based Reynolds numbe
 r. This can be quantitatively interpreted with the help of the properties 
 of the rate of strain conditioned on the vorticity\, leading to a very goo
 d description of numerical results up to the highest Taylor Reynolds numbe
 r studied (1\,300).&nbsp\;\n&nbsp\;The nonlocal relation between strain an
 d vorticity appears as a major difficulty to provide a quantitative descri
 ption of the flow properties. To investigate this non-locality\, we decomp
 ose the strain-rate tensor into nonlocal and a local contributions\, obtai
 ned by performing the Biot-Savart integral over a sphere of radius R. Our 
 numerical results reveal that the local strain\, surprisingly\, counteract
 s the amplification of very intense vortices. This uncovered self-attenuat
 ion mechanism potentially provides a direction in establishing the regular
 ity of the Navier-Stokes equations.
LOCATION:Seminar Room 1\, Newton Institute
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