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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:On describing mean flow dynamics in wall turbulenc
 e - Klewicki\, J (New Hampshire)
DTSTART;TZID=Europe/London:20080911T165000
DTEND;TZID=Europe/London:20080911T171000
UID:TALK13384AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/13384
DESCRIPTION:The study of wall-flow dynamics and their scaling 
 behaviors with increasing Reynolds number warrants
  considerable attention. Attempts to date\, howeve
 r\, have primarily focused on questions relating t
 o what scaling behaviors occur\, rather than the d
 ynamical reasons why they occur. Given these consi
 derations\, the present talk is organized in three
  parts. In the first part it is shown that the pre
 dominant methodology for discerning the dominant m
 echanisms associated with the mean flow dynamics i
 s problematic\, and can lead to erroneous conclusi
 ons. In the second part we examine the Millikan-Iz
 akson (inner/outer/overlap) arguments that underpi
 n the widely accepted derivation for a logarithmic
  mean profile. Existing rigorous results from the 
 theory of functions are outlined. They reveal that
  the Millikan-Izakson arguments constitute somethi
 ng very close to a tautology and embody little phy
 sics specific to turbulent wall-flows. The first t
 wo parts establish the context for the third. The 
 presentation concludes with a physical interpretat
 ion of the mathematical conditions necessary for a
  logarithmic (or nearly logarithmic) mean profile.
  The basis for this interpretation is the analysis
  of Fife et al.\, (2005 JFM 532}\, 165) which reve
 als that the mean differential statement of Newton
 s second law rigorously admits a hierarchy of phys
 ical layers each having their own characteristic l
 ength. These analyses show that the condition for 
 exact logarithmic dependence exists when the norma
 lized equations of motion (normalized using the lo
 cal characteristic length) attain a self-similar s
 tructure\, and physically indicate that the leadin
 g coefficient in the logarithmic law (von Karman c
 onstant) will only be truly constant when an exact
  self-similar structure in the gradient of the tur
 bulent force is attained across a range of layers 
 of the hierarchy. These results are discussed rela
 tive to the physics of boundary layer Reynolds num
 ber dependence and recent data indicating that the
  von Karman constant varies for vary ing mean mome
 ntum balance.
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:Mustapha Amrani
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