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Wednesday, June 04, 2008
10:00 AM - 11:00 AM
CNLS Conference Room (TA-3, Bldg 1690)

Seminar

Intermittency, accuracy, and modeling of homogeneous and passive scalar turbulence

Toshiyuki Gotoh
Department of Scientific and Engineering Simulation, Graduate School of Engineering, Nagoya Institute of Technology, Japan

Statistical properties of the velocity and passive scalars in homogeneous turbulence are studied using very high resolution DNS. In particular, scaling properties of low and moderate order moments of the velocity and scalar increments in the inertial range are examined from the viewpoint of numerical accuracy, Reynolds number dependence, and universality. It is found that the scaling exponents of moments of the longitudinal and transverse velocity increments and scalar increments approach their asymptotic values at different rates as the order of the moment or the Reynolds number is increased.

Differences can also be detected in the numerical accuracy to which these moments can be computed. By changing the spatial resolution up to 20483 grid points while maintaining a constant Reynolds number R ≈ 180 or 420 and constant Schmidt number Sc = 1, we have examined the effects of the spatial resolution on the derivative fields, spectrum, low to moderate order scaling exponents, and probability density functions. It is found that the spectra and scaling exponents of the structure functions up to the eighth order in the range of scales greater than 10 are insensitive to variations in Kmax , even when Kmax ≃ 1.

Degradation of the statistics arises from modifications of the flow dynamics due to the wavenumber cutoff, which is within the dissipation range. By using high resolution DNS data, the effects of the subgrid scales on the grid scales are examined, and Langevin type modeling of the subgrid degrees of freedom is explored using statistical projection operators.

Host: Daniel Livescu, CCS-2