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SUMMARY:Grid Turbulence: How Important are Initial Conditions? - Philippe 
 Lavoie\, Flow Control Group\, Imperial College London
DTSTART:20080501T131500Z
DTEND:20080501T150000Z
UID:TALK11620@talks.cam.ac.uk
CONTACT:8442
DESCRIPTION:The importance of initial conditions in turbulent flows is a c
 ontentious issue\, which could have important ramifications relative to ou
 r understanding of turbulence and its modelling. This is particularly true
  for the idealised case of homogeneous isotropic turbulence (HIT). An impo
 rtant theoretical result for HIT is that the turbulence decays following a
  power-law\, with some support for the universality of the power-law expon
 ent. However\, recent theoretical\, numerical and experimental studies hav
 e argued against such a universality. The present study attempts to addres
 s these issues and resolve a number of ambiguities found in the literature
  for decaying grid turbulence and its relation to the ideal case of decayi
 ng HIT. Extensive measurements of the turbulence decay downstream of vario
 us grids were undertaken with and without a secondary contraction to inves
 tigate systematically the effect of initial conditions for this flow. It w
 ill be shown that the turbulence only decays following a self-similar mann
 er approximately. It is demonstrated that grid turbulence decays following
  a non-universal power-law. However\, we argue that the decay would be uni
 versal should the turbulence be truly homogeneous and isotropic\, although
  a dependence on R-lambda is expected. This dependence should disappear as
 ymptotically as the Reynolds number goes to infinity.
LOCATION:Lecture Room 6\, Engineering Department
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