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SUMMARY:On helical multiscale characterisation of homogeneous turbulence -
  Schneider\, K\, Jacobitz\, F\, Bos\, W (Aix-Marseille U\; U. San Diego\; 
 Ecole Centrale Lyon\; ENS\, Paris)
DTSTART:20120723T104500Z
DTEND:20120723T110500Z
UID:TALK39010@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:The helical properties of five prototypical homogeneous turbul
 ent flows are investigated: statistically steady forced isotropic turbulen
 ce\, decaying isotropic turbulence\, decaying rotating turbulence\, growin
 g sheared turbulence\, and growing rotating sheared turbulence with a rota
 tion ratio f/S = +0.5. The five turbulent flows were originally studied us
 ing direct numerical simulations. An orthogonal wavelet decomposition is u
 sed to study the scale-dependent properties of the cases. For comparison\,
  a solenoidal uncorrelated Gaussian random field is included in the analys
 is as a sixth case. It was found that flows with growing turbulent kinetic
  energy and turbulent motion at large scales show a maximum in the velocit
 y helicity probability distribution functions (PDFs) at zero\, correspondi
 ng to a trend to local two-dimensionalization of the flow with vorticity a
 nd velocity being perpendicular. Flows with decaying turbulent kinetic ene
 rgy and turbulent motion at small scales\, how ever\, show maxima of the v
 elocity helicity PDFs at plus and minus one\, indicating a preference for 
 helical motion with alignment or anti-alignment of vorticity and velocity.
  The PDFs of vorticity helicity always assume maxima at plus and minus for
  all flows. Joint PDFs of relative velocity helicity and relative vorticit
 y helicity show that the quantities tend to have the same sign for all flo
 ws including the random field\, indicating that vorticity helicity dissipa
 tes velocity helicity.\n
LOCATION:Seminar Room 1\, Newton Institute
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