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SUMMARY:Kinetic theory representation for turbulence modeling and computat
 ion - Chen\, H (Exa Corporation)
DTSTART:20080929T103000Z
DTEND:20080929T110000Z
UID:TALK13832@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:One of the most common approximations in turbulence for the av
 eraged effect of small scales is by the so called eddy viscosity modeling.
  That is\, one approximates the Reynolds stress as a linear function of th
 e local rate of strain of the averaged flow field. The proportionality con
 stant is referred to as an eddy viscosity. This concept was first proposed
  over a century ago. It stems from an analogy for small eddy interactions 
 with collisions of molecules resulting in Newtonian fluid constitutive rel
 ations. This approximation has made enormous impact particularly in comput
 ational fluid dynamics for turbulent flows. Many theoretical works were al
 so developed since then\, with various successes\, in order to analyticall
 y derive such a functional relationship. However\, unlike molecular intera
 ctions in a fluid\, one of the apparent criticisms or difficulties in this
  analogy is the lack of scale separations between averaged fluid motions a
 nd fluctuating eddies. In this presentation\, the speaker will give a some
 what provocative argument in favor of such analogy\, provided that this co
 ncept be expanded in a generalized kinetic theory framework. In such an ex
 panded framework\, the analogy between eddy interactions and molecular col
 lisions has a broader physical validity\, while the eddy viscosity approxi
 mation is its consequence in the very long wave length limit. The kinetic 
 theory representation itself needs not depend on scale separations. Using 
 such an expanded analogy\, one can also draw similarities between turbulen
 t flow phenomena to that of non-Newtonian fluid flows in micro/nano scales
 . Nevertheless\, other than phenomenological argument\, as far as the spea
 ker is aware\, so far there have been little theoretical attempts to produ
 ce such a kinetic theory for turbulence on a concrete footing via first pr
 inciple\, if its physical soundness is acceptable.
LOCATION:Seminar Room 1\, Newton Institute
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