0227 点源熱拡散における乱流拡散係数のレイノルズ数依存性について(OS2-6 乱流の計測・解析・制御,オーガナイズドセッション)

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Homogeneous quasi-isotropic turbulence fields ranged R_λ=26.1〜406 were generated in a laboratory wind tunnel, covering from small-scale grid turbulence to large-scale turbulence suitable to simulate such as the atmospheric-diffusion fields. Temperature and two velocity components were simultaneously measured behind a thermal plume continuously ejected from a thin pipe of 5.4mm in diameter. The diffusion field developed from short-time diffusion to long time diffusion as it flow downstream. The dependence of turbulent diffusion coefficient K on R_λ was estimated The diffusion coefficient grew larger from K=4.9 to 602cm^2/s as R_λ increased from 26.1 to 406. The growth rate of K, changed as the turbulent Reynolds number exceeded R_λ≒200. The fact corresponds to the shift from the short-time diffusion to the long-time one.
2009-11-06