報告書番号

T99073

タイトル（和文）

排ガスの濃度変動を対象とした大気拡散予測手法の開発（その５） -－風洞実験による瞬間高濃度特性の解明－-

タイトル（英文）

Atmospheric diffusion evaluation method for stack gas incorporating concentration fluctuation effects(5)-Characteristics of peak concentration measured in wind tunnel experiments-

概要 （図表や脚注は「報告書全文」に掲載しております）

平地，立方体建物，配管系建物を対象とした風洞実験より，プルームが濃度変動に与える影響を考慮し，確率分布関数および高濃度の特性を明らかにした。ゼロ濃度を除いた条件付き範囲の濃度変動強度は，ゼロ濃度を含む全領域の分布に比較して鉛直方向の変化が小さく1前後の値を示し，プルームの間欠性による影響はプルーム内の乱流混合による影響に比べ相対的に大きい。また，濃度変動強度と確率分布関数には密接な関係があり，濃度変動強度が等しい位置では，平地，建物周辺に拘わらず確率分布関数は同じ分布を示す。濃度の確率分布関数は，濃度変動強度が0.3～1.5のプルーム中心付近では対数正規分布，濃度変動強度が1.5以上のプルーム端では指数分布に近い分布形状を有し，そのためプルーム内における高濃度比は常に濃度変動強度の5倍程度の値を示す。このことより濃度の平均値および標準偏差より高濃度を簡便に予測できることが明らかとなった。

概要 （英文）

Measurements of concentration fluctuation were made in a plume from a point source in a simulated neutral atmospheric boundary layer. The concentration fluctuation intensity, defined as the ratio of concentration standard deviation to mean concentration, is smallest on the plume centerline and increases toward the edges of the plume. This variation in intensity is strongly affected by the intermittency factor, defined as the proportion of the time that shows non-zero concentration. Conditional statistics calculated from significantly non-zero concentrations vary only slightly in the plume. The cumulative probability distribution function (CDF) of concentration is one of the most useful of the concentration fluctuation statistics because it includes mean concentration, variance, and intermittency. There are three standard mathematical forms of CDF that are frequently applied to concentration fluctuation data: exponential distribution, lognormal distribution, and clipped normal distribution. The lognormal distribution is a reasonable fit for measurements in the regions where the concentration fluctuation intensity is between 0.3 and 1.5, and the exponential distribution a fit in the regions where the concentration fluctuation intensity is over 1.5. Therefore, the peak-to-mean concentration ratio in a plume is always about 5 times the concentration fluctuation intensity.

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