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CATEGORIES:Isaac Newton Institute Seminar Series
SUMMARY:Statistics of two-point velocity difference in hig
h-resolution direct numerical simulations of turbu
lence in a periodic box - Ishihara\, T (Nagoya)
DTSTART;TZID=Europe/London:20080930T143000
DTEND;TZID=Europe/London:20080930T150000
UID:TALK13842AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/13842
DESCRIPTION:Statistics of two-point velocity difference are st
udied by analyzing the data from high-resolution d
irect numerical simulations (DNS) of turbulence in
a periodic box\, with up to $4096^3$ grid points.
The DNS consist of two series of runs\; one is wi
th $k_{max}ta im 1$ (Series 1) and the other is w
ith $k_{max}ta im 2$ (Series 2)\, where $k_{max}$
is the maximum wavenumber and $ta$ the Kolmogoro
v length scale. The maximum\, time-averaged\, Tayl
or-microscale Reynolds number $R_lambda$ in Series
1 is about 1145\, and it is about 680 in Series 2
. Particular attention is paid to the possible Rey
nolds number ($Re$) and $r$ dependence of the stat
istics\, where $r$ is the distance between two poi
nts. The statistics include the probability distri
bution functions (PDFs) of velocity differences an
d the longitudinal and transversal structure funct
ions. DNS data suggest that the PDFs of the longit
udinal velocity difference at different values of
Re but the same values of $r/L$\, where $L$ is the
integral length scale\, overlap well with each ot
her when r is in the inertial subrange and when us
ing the same method of forcing at large scales. Th
e similar is also the case for the transversal vel
ocity difference. The tails of the PDFs of normali
zed velocity differences ($X$'s) are well approxim
ated by such a function as $xp(-A|X|^a)$\, where
$a$ and $A$ depend on $r$\, and where $a$ becomes
$pprox 1$ in the inertial subrange. Analysis show
s that the scaling exponents of the $n$th-order lo
ngitudinal and transversal structure functions are
not sensitive to $Re$ but sensitive to the large-
scale anisotropy and non-stationarity\, and sugges
ts that nevertheless their difference is a decreas
ing function of $Re$.
LOCATION:Seminar Room 1\, Newton Institute
CONTACT:Mustapha Amrani
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