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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:On helical multiscale characterisation of homogene
ous turbulence - Schneider\, K\, Jacobitz\, F\, Bo
s\, W (Aix-Marseille U\; U. San Diego\; Ecole Cent
rale Lyon\; ENS\, Paris)
DTSTART;TZID=Europe/London:20120723T114500
DTEND;TZID=Europe/London:20120723T120500
UID:TALK39010AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/39010
DESCRIPTION:The helical properties of five prototypical homoge
neous turbulent flows are investigated: statistica
lly steady forced isotropic turbulence\, decaying
isotropic turbulence\, decaying rotating turbulenc
e\, growing sheared turbulence\, and growing rotat
ing sheared turbulence with a rotation ratio f/S =
+0.5. The five turbulent flows were originally st
udied using direct numerical simulations. An ortho
gonal wavelet decomposition is used to study the s
cale-dependent properties of the cases. For compar
ison\, a solenoidal uncorrelated Gaussian random f
ield is included in the analysis as a sixth case.
It was found that flows with growing turbulent kin
etic energy and turbulent motion at large scales s
how a maximum in the velocity helicity probability
distribution functions (PDFs) at zero\, correspon
ding to a trend to local two-dimensionalization of
the flow with vorticity and velocity being perpen
dicular. Flows with decaying turbulent kinetic ene
rgy and turbulent motion at small scales\, how eve
r\, show maxima of the velocity helicity PDFs at p
lus and minus one\, indicating a preference for he
lical motion with alignment or anti-alignment of v
orticity and velocity. The PDFs of vorticity helic
ity always assume maxima at plus and minus for all
flows. Joint PDFs of relative velocity helicity a
nd relative vorticity helicity show that the quant
ities tend to have the same sign for all flows inc
luding the random field\, indicating that vorticit
y helicity dissipates velocity helicity.\n
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:Mustapha Amrani
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