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SUMMARY:Stability in a plane channel flow with viscosity stratification - 
 Sameen\, A (ICTP)
DTSTART:20080912T094000Z
DTEND:20080912T100000Z
UID:TALK13383@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:We discuss the stability of a channel flow with viscosity stra
 tification. Three mechanisms of route to transition\, namely linear\, tran
 sient and secondary instability growths are investigated here. How does a 
 viscosity-stratification alter the stability behaviour of these mechanisms
  in a channel flow? A temperature dependent viscosity is used obtain the v
 iscosity gradients. It is concluded that all three routes to transition ha
 s different stability characteristics for any given kind of stratification
 . From linear stability results\, it has been accepted that heat diffusivi
 ty does not affect stability. However\, we show that realistic Prandtl num
 bers cause a transient growth of disturbances that is an order of magnitud
 e higher than at zero Prandtl number. Buoyancy\, even at fairly low levels
 \, gives rise to high levels of subcritical energy growth. Unusually for t
 ransient growth\, both of these are spanwise-independent and not in the fo
 rm of streamwise vortices. At moderate Grashof numbers\, exponential growt
 h dominates\, with distinct Rayleigh-Benard and Poiseuille modes for Grash
 of numbers upto $ im 25000$\, which merge thereafter. We conclude that a k
 nowledge of transition mechanism and type of stratification is necessary f
 or viscosity variation to be exploited as an effective flow control mechan
 ism.
LOCATION:Seminar Room 1\, Newton Institute
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