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DNS OF TURBULENT CHANNEL FLOW AT VERY LOW REYNOLDS NUMBERS

Takahiro Tsukahara
Tokyo University of Science

Yohji Seki
Department of Mechanical Engineering, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba 278-8510, Japan

Hiroshi Kawamura
Department of Mechanical Engineering Faculty of Science and Technology Science University of Tokyo Noda-shi, Chiba 278 Japan

Daisuke Tochio
Department of HTTR Project, Oarai Research Establishment, Japan Atomic Energy Research Institute Oarai-machi, Higashiibaraki-gun, Ibaraki 311-1394, Japan

Abstract

Direct numerical simulation (DNS) of a fully developed turbulent channel flow for very low Reynods numbers has been executed with larger computational box-sizes than those of common DNS. The present Reynolds number is decreased down to Reτ = 64, where Reτ is based on the friction velocity and the channel half width δ. For Reτ = 80 with using the largest box of 51.2δ × 2δ × 22.5δ, the periodic weak-turbulence regions are observed. This type of locally disordered flow is similar to a turbulent puff observed in a transitional pipe flow. Various turbulence statistics such as turbulent intensities, vorticity fluctuations, Reynolds stresses are provided. Especially, their near-wall asymptotic behavior and budget terms of turbulence kinetic energy are obtained and discussed with respect to Reynolds number dependence and an influence of the comptational box-size. In addition, two-point correlation coefficients, visualized instantaneous flow fields and the pre-multiplied energy spectra are presented in order to examine turbulence structures.