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SUMMARY:The existence of very-large scale motions or `superstructures' in 
 wall-bounded turbulent flows - Hutchins\, N (Melbourne)
DTSTART:20080911T130000Z
DTEND:20080911T132000Z
UID:TALK13373@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Recent experiments in the logarithmic and wake regions of wall
 -bounded turbulent flows have revealed the existence of very large-scale m
 otions (with instantaneous length-scales up to 20 boundary layer thickness
 es). This regime of very long meandering positive and negative streamwise 
 velocity fluctuations (and associated roll-modes) appear to be universal f
 eatures of all wall-bounded turbulent flows\, having been recently documen
 ted in turbulent boundary layers\, pipes\, channels and atmospheric surfac
 e layers. Importantly\, these structures appear to maintain a presence or 
 footprint in the near-wall region\, seeming to modulate or influence the n
 ear-wall cycle. As Reynolds number increases\, not only is there an increa
 se in scale-separation between these large-scale motions and the near-wall
  cycle\, but also an increase in the overall energy of these long meanderi
 ng features as compared to the viscous scales. This would seem to imply th
 at these features will play an increasingly dominant role in high Reynolds
  number wall-bounded turbulent flows.
LOCATION:Seminar Room 1\, Newton Institute
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