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SUMMARY:CVS filtering to study turbulent mixing - Farge\, M (LMD-CNRS-IPSL
 )
DTSTART:20080930T143000Z
DTEND:20080930T150000Z
UID:TALK13844@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Coherent Vortex Simulation (CVS) is based on the wavelet filte
 red Navier-Stokes equations\, where at each instant the turbulent flow is 
 split into two orthogonal contributions: the coherent flow made of vortice
 s which is kept\, and the incoherent flow made of the background fluctuati
 ons which is discarded. The CVS filter is based on an orthogonal wavelet d
 ecomposition of the vorticity field where only the wavelet coefficients wh
 ose modulus is larger than a given threshold are kept. The value of the th
 reshold depends only on the total enstrophy and on the numerical resolutio
 n used to represent the flow.\n\nThe CVS filter has already been applied t
 o 2D [Farge\, Schneider and Kevlahan in Phys. Fluids 11(8) 1999] and 3D [F
 arge\, Pellegrino and Schneider in Phys. Rev. Lett. 87(55) 2001\, Farge et
  al. in Phys. Fluids 15(10) 2003\, Okamoto et al. in Phys. Fluids 19 2007]
  turbulent flows\, where it has been shown that only few wavelet coefficie
 nts (from 0.7% for 256^2 up to 2.6% for 2046^3 resolution) are sufficient 
 to represent the coherent flow which preserves the vorticity and velocity 
 PDFs\, the energy spectrum and the nonlinear transfers all along the inert
 ial range.\n\nWe will analyze the time evolution of a decaying homogeneous
  isotropic turbulent flow\, by applying the CVS filter at each time step o
 f a Direct Numerical Simulation (DNS). We will compare the Eulerian and La
 grangian mixing properties of the total\, coherent and incoherent flows by
  studying how they advect a passive tracer and many particles during sever
 al eddy turn-over times. We will quantify the mixing properties of coheren
 t and incoherent flows and show that efficient mixing is due to the transp
 ort by vortices\, while the incoherent contribution is much weaker and onl
 y diffusive.\n\nRelated Links\n    * http://wavelets.ens.fr - Web
LOCATION:Seminar Room 1\, Newton Institute
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