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(流体工学,流体機械)

抄録

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.