フラクタル格子により生成されるマルチスケール誘起乱流の構造とスカラー拡散機構: 第2報，DNSによる一様等方性と間欠性に及ぼす格子パラメータの影響の検討

摘要

自己相似的な形状を有する乱流格子によって生成rnされた乱流（フラクタル格子乱流）の性質が風洞実験rnにより調べられ，その特徴として，高いRe_λ（＝rnu_(rms)λ/v）を有すること，主流方向に対する乱流特性rn長の不変性および散逸定数の特異性が主に挙げられrnている．%Turbulence characteristics in the spatially developing fractal-generated turbulence are investigated by means of the direct numerical simulation (DNS). The square type fractal grids are numerically constructed using the immersed boundary method. The effects of solidity σ and thickness ratio t_r, which are ones of the most important grid parameters for fractal grids, are investigated in detail. The results show that the increase of σ leads to the improvement of the uniformity and isotropy of flow fields. The integral length scale in the decaying region of the fractal-generated turbulence remains monotone increase at high σ and t_r, whereas it is approximately constant at low σ and t_r. The derivative skewness and flatness in the streamwise direction are different from those in the transverse direction for all σ and t_r investigated. These results will be useful for designing fractal grids for practical applications.