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SUMMARY:Intermittency and scaling of passive scalar convected by isotropic
  steady turbulence under the uniform mean scalar gradient - Gotoh\, T (Nag
 oya Institute of Technology)
DTSTART:20081002T103000Z
DTEND:20081002T110000Z
UID:TALK13862@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION: It has been more convincing that passive scalar in turbulence
  is more intermittent than the turbulent velocity field itself\, implying 
 that the small scales of the passive scalar are more affected by the large
  scale conditions. In order to get more precise knowledge about the scalin
 g behavior of the passive scalar for various Reynolds (Peclet) numbers and
  large scale conditions\, we have performed very high resolution direct nu
 merical simulations (DNSs) of the passive scalar turbulence with or withou
 t uniform mean scalar gradient up to $2048^3$ grid points and $R_lambdapp
 rox 600$\, and analysed the various statistical functions. Turbulent veloc
 ity field was statistically in a steady and isotropic state by Gaussian ra
 ndom force applied at large scales. Fundamental statistics such as the spe
 ctra of the kinentic energy\, pressure\, scalar variance\, scalar-velocity
  flux were examined\, especially in their scaling behavior.\n\nIt is found
  that although curves of the kinetic energy and scalar spectra are well co
 llapsed onto a single curve when the Kolmogorov variables are used\, while
  the others are not as well as the former\, suggesting need of more elabor
 ated scaling. The scaling of the velocity structure functions is consisten
 t with the existing data of experiments and DNSs\, while the scaling of th
 e passive scalar is not convincing and difficult to reach definite conclus
 ion. When the isotropic random injection for the passive scalar is applied
  at large scales (Case R)\, each curve of the local scaling exponent at a 
 given order has one local minimum and maximum point\, unlike the velocity 
 case\, and plateau is not wide enough to precisely determine the scaling e
 xponents. On the other hand\, when the uniform mean scalar gradient is app
 lied (Case G)\, the curves of the local scaling exponents of the isotropic
  sector are found to have well developed plateau\, and their plateau level
 s are smaller than those of Case R\, meaning stronger intermittency for th
 e Case of G. Crossover of the velocity and scalar structure functions is a
 lso examined. The crossover of the transverse velocity structure functions
  is found to be very similar to that of the passive scalar. We seek the re
 ason for the above differences and similarities. 
LOCATION:Seminar Room 1\, Newton Institute
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