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SUMMARY:The ecology of transitional turbulence - Nigel Goldenfeld\, Physic
 s\, University of Illinois
DTSTART:20141105T133000Z
DTEND:20141105T143000Z
UID:TALK56068@talks.cam.ac.uk
CONTACT:Aurelia Honerkamp-Smith
DESCRIPTION:How do fluids become turbulent as their flow velocity is incre
 ased? In\nrecent years\, careful experiments in pipes and Taylor-Couette s
 ystems\nhave revealed that the lifetime of transient turbulent regions in 
 a\nfluid appears to diverge with flow velocity just before the onset of\nt
 urbulence\, faster than any power law or exponential function. I show\nhow
  this superexponential scaling of the turbulent lifetime in pipe flow\nis 
 related to extreme value statistics\, which I show is a manifestation\nof 
 a mapping between transitional turbulence and the statistical\nmechanics m
 odel of directed percolation. This mapping itself arises from\na further s
 urprising and remarkable connection: laminar and turbulent\nregions in a f
 luid behave as a predator-prey ecosystem. Such ecosystems\nare governed by
  individual fluctuations in the population and being\nnaturally quantized\
 , are solvable by path integral techniques from field\ntheory. I explain t
 he evidence for this mapping\, and propose how a\nunified picture of the t
 ransition to turbulence emerges in systems\nranging from turbulent convect
 ion to magnetohydrodynamics.
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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