AM05-14-001 2粒子拡散と乱流構造に関する数値的研究(乱流熱物質移動および反応流1,一般講演)

概要

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The purpose of this study is to elucidate the relation between a growth of two-particle distance and the fine-scale structures of turbulence by the three-dimensional direct numerical simulation. It is shown that the Lagrangian bursts of particle-pair occur in the straining stagnation region, where Δ<0 (here, Δ=(Q/3)^3+(R/2)^2 with Q and R being the 2nd and 3rd invariance of the velocity gradient tensor). The volume fraction of the straining stagnation region is about 60% for the present turbulence of Re_λ=120. The scaling law of <(Δl)^2)〜Τ^γ (Δl and Τ are the increment of separation distance and the diffusion time, respectively) has been also investigated. It is found that the relation γ=6/D_s is useful, where D_s is the power exponent of n_s≈C_sL^<-3>(L/η)^<D_s> (L and η are the integral length scale and Kolmogorov microscale, respectively; n_s is the number density of straining stagnation points; C_s is a dimensionless number). Further, it is shown that the trajectories of particle-pairs in the (Q, R) space are useful to recognize the fine-scale structure bearing the Lagrangian burst of particle-pair.
日本流体力学会の論文
2005-09-05