壁近傍乱流における壁近傍層の乱流特性

概要

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Model simulations to show autonomous property of near-wall layer below lower edge of logarithmic layer are conducted for a channel flow. A model to remove interaction between two layers top and below of a plane parallel to the wall, by assuming zero wall-normal velocity on it is employed for this purpose. It turned out that near-wall layer needs a definite minimum thickness to maintain turbulent regime if no interaction with upper layer is allowed and that the layer has universal turbulent structure if turbulent regime is allowed irrespective of any interaction with above layer. The universality holds for any wall condition such as to lower wall friction, with different structure depending on each wall condition. Simulations to trace time evolution of a small pair of quasi-streamwise vortices submerged in a laminar flow of mean turbulent velocity distribution were also conducted to see the basic structure of the universal near-wall turbulence. The energy budged of the grown-up structure which is composed of a couple of hairpin vortices and subsidiarily generated quasi-streamwise vortices is similar to that observed in natural turbulent channel flow.
2000-10-25