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Eighth International Symposium on Turbulence and Shear Flow Phenomena
August, 28-30, 2013, Poitiers, Futuroscope, France

DOI: 10.1615/TSFP8

DNS OF A TRANSITIONALLY ROUGH CHANNEL FLOW WITH A 3-D ROUGHNESS

pages 1-6
DOI: 10.1615/TSFP8.1840
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Краткое описание

A DNS study is performed to investigate turbulence in a steady-state channel flow at transitionally rough region (ks+ = 8 − 41) with a smooth top surface and a roughened bottom surface made of close-packed pyramids at several Reynolds numbers. Simulations in a channel with all smooth walls are also conducted to facilitate direct comparison. The skin friction factor results show an inflection point at ks+ ~ 15. Reynolds stress and normal vorticity show a similarity in the logarithmic region. In the outer layer, however, it appears that small- and large-scales structures exhibit different sensitivities to the existence of roughness. While the dissipation and vorticity, which are representing the small-scale structures, collapse to the corresponding smooth-wall values, Reynolds stress quantities containing great contributions of the large-scale structures do not exhibit this behaviour for δ/kt = 20 cases. The rough-case with δ/kt = 40, however, represents greater tendency to the similarity. Flow field patterns in the roughness sublayer demonstrate a significant dependence on Reynolds number. Also, at y/k = 0.4 above the crest, the flow structure of the case Reτ = 670, ks+ = 41 is very similar to that of Reτ = 3520, δ/kt = 54.4, ks+ = 95 in the experimental fully-rough results Hong et al. (2011).

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