低レイノルズ数におけるｄ形粗面乱流境界層の組織構造（ＶＩＴＡ法による解析と統計量）

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  • The coherent structure of a turbulent boundary layer over a d-type rough surface at a low Reynolds number. (Analysis with the VITA technique and statistical charcteristics)
  • テイ レイノルズスウ ニ オケル dガタ ソメン ランリュウ キョウカイソウ

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Conditional averages of longitudinal, normal velocity and of their products have been obtained in a turbulent boundary layer over a d-type rough surface at a momentum thickness Reynolds number of Rθ&elDot;800. Averaged properties, like probability density distribution, higher order moments etc. are also provided in order to yield information related to coherent structures. It is shown that the ensemble averaged patterns reflect the well known ejection and sweep events, even in the present low Reynolds number flow. Those ejections and sweeps both made strong, intermittent contributions to the Reynolds stress and turbulence production. Near the wall, the ejection phase plays a predominant role. The normalized averaged bursting frequency is larger for the present rough wall flow than for the smooth wall flow at almost the same Reynolds number. It is inferred from the increase of both the width of intermittent region and the entrainment rate that the width of highly irregular interface between turbulent and non-turbulent flow increases with a decreasing Reynolds number.

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