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SUMMARY:Statistics of two-point velocity difference in high-resolution dir
 ect numerical simulations of turbulence in a periodic box - Ishihara\, T (
 Nagoya)
DTSTART:20080930T133000Z
DTEND:20080930T140000Z
UID:TALK13842@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Statistics of two-point velocity difference are studied by ana
 lyzing the data from high-resolution direct numerical simulations (DNS) of
  turbulence in a periodic box\, with up to $4096^3$ grid points. The DNS c
 onsist of two series of runs\; one is with $k_{max}ta im 1$ (Series 1) an
 d the other is with $k_{max}ta im 2$ (Series 2)\, where $k_{max}$ is the 
 maximum wavenumber and $ta$ the Kolmogorov length scale. The maximum\, ti
 me-averaged\, Taylor-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 Reynolds number ($Re$) and $r$ dependence of the statisti
 cs\, where $r$ is the distance between two points. The statistics include 
 the probability distribution functions (PDFs) of velocity differences and 
 the longitudinal and transversal structure functions. DNS data suggest tha
 t the PDFs of the longitudinal 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 other when r is in the inertial subrange and when 
 using the same method of forcing at large scales. The similar is also the 
 case for the transversal velocity difference. The tails of the PDFs of nor
 malized velocity differences ($X$'s) are well approximated by such a funct
 ion as $xp(-A|X|^a)$\, where $a$ and $A$ depend on $r$\, and where $a$ be
 comes $pprox 1$ in the inertial subrange. Analysis shows that the scaling
  exponents of the $n$th-order longitudinal and transversal structure funct
 ions are not sensitive to $Re$ but sensitive to the large-scale anisotropy
  and non-stationarity\, and suggests that nevertheless their difference is
  a decreasing function of $Re$.
LOCATION:Seminar Room 1\, Newton Institute
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