Prediction of the upper tail of concentration distributions of a continuous point source release in urban environments

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• 作者：G. C. Efthimiou ; S. Andronopoulos ; I. Tolias…
• 关键词：Concentration distribution ; CFD–RANS ; Wind tunnel ; Hazard assessment
• 刊名：Environmental Fluid Mechanics
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：16
• 期：5
• 页码：899-921
• 全文大小：2,578 KB
• 刊物类别：Earth and Environmental Science
• 刊物主题：Environment
  Environmental Physics
  Mechanics
  Hydrogeology
  Meteorology and Climatology
  Oceanography
  
• 出版者：Springer Netherlands
• ISSN：1573-1510
• 卷排序：16

文摘

The peak values observed in a measured concentration time series of a dispersing gaseous pollutant released continuously from a point source in urban environments, and the hazard level associated with them, demonstrate the necessity of predicting the upper tail of concentration distributions. For the prediction of concentration distributions statistical models are preferably employed which provide information about the probability of occurrence. In this paper a concentration database pertaining to a field experiment is used for the selection of the statistical distribution. The inverses of the gamma cumulative distribution function (cdf) for 75th–99th percentiles of concentration are found to be more consistent with the experimental data than those of the log-normal distribution. The experimental values have been derived from measured high frequency time series by sorting first the concentrations and then finding the concentration which corresponds to each probability. Then the concentration mean and variance that are predicted with Computational Fluid Dynamics-Reynolds Averaged Navier–Stokes (RANS) methodology are used to construct the gamma distribution. The proposed model (“RANS-gamma”) is included in the framework of a computational code (ADREA-HF) suitable for simulating the dispersion of airborne pollutants over complex geometries. The methodology is validated by comparing the inverses of the model cdfs with the observed ones from two wind tunnel experiments. The evaluation is performed in the form of validation metrics such as the fractional bias, the normalized mean square error and the factor-of-two percentage. From the above comparisons it is concluded that the overall model performance for the present cases is satisfactory.