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Second moment modelling for the numerical simulation of passive scalar dispersion of air pollutants in urban environments

机译：二阶矩模型用于城市环境中空气污染物被动标量扩散的数值模拟

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摘要

Since the Industrial Revolution mankind has needed to deal with increasing air pollution problems as a result of manufacturing, mining, transportation, and power production. Air pollution concerns the interaction of gases and particles emitted into the atmosphere with the surrounding environment. This interaction can redirect pollutants toward sensitive areas, concentrate different species above acceptable levels, or even mitigate concentration levels by enhancing diffusion and dispersion. The present EU environmental legislation has been implemented to control these high pollutant concentrations and improve the air quality conditions in urban areas. The numerical simulation of dispersion has shown to be a useful tool for both the scientific description of pollution phenomena and for planning and decision making.The numerical simulation of pollution dispersion in urban environments by means of solution of the statistically steady Reynolds Averaged Navier Stokes (RANS) equations is known to be strongly dependent on turbulence models. If pollution dispersion is modelled, the turbulence models do not only have to be used for the Reynolds stresses, but also for the turbulent scalar fluxes. While the influence of several turbulence models for Reynolds stresses on pollution dispersion in urban environments has already been examined several times, the turbulent scalar fluxes are usually modelled by the simple gradient diffusion assumption. In the present work, the influence of more advanced models for the turbulent scalar fluxes on the dispersion of pollutants is examined. Two different wind tunnel experiments, a two-dimensional (2D) street canyon and a three-dimensional (3D) urban area model, were selected for the validation of the modelsu27 performance. In total, five anisotropic algebraic flux models and two second moment models were implemented in the commercial software FLUENT 6.3. All these models together with the simple gradient diffusion model (with different turbulent Schmidt numbers) are used and the results are compared with measurements using statistical performance measures to assess their predictive capability. All evaluated models showed good general agreement in comparison to the experiments. The anisotropic models provided better concentration predictions than the isotropic models in 2D simulations. However, these improvements were very small in 3D simulations and usually disappeared. In the end, modelling improvements based on the sensitivity analysis of model coefficients, numerical and experimental model limitations and other parameters and assumptions relevant for the simulation of passive scalar pollution dispersion are presented and discussed.
机译：自工业革命以来，人类需要应对制造，采矿，运输和电力生产带来的日益严重的空气污染问题。空气污染涉及排放到大气中的气体和颗粒与周围环境的相互作用。这种相互作用可以将污染物重定向到敏感区域，将不同的物种集中在可接受的水平以上，甚至通过增强扩散和扩散来减轻其浓度水平。现行的欧盟环境法规已经实施，以控制这些高污染物浓度并改善城市地区的空气质量状况。扩散的数值模拟已被证明是对污染现象的科学描述以及规划和决策的有用工具。通过统计稳定的雷诺兹平均Navier Stokes（RANS）的求解，对城市环境中的污染扩散进行数值模拟。 ）已知方程强烈依赖于湍流模型。如果对污染扩散进行建模，则不仅必须将湍流模型用于雷诺应力，而且还要将湍流用于标量通量。虽然已经多次研究了几种湍流模型对雷诺应力对城市环境中污染物扩散的影响，但通常采用简单的梯度扩散假设来建模湍流标量通量。在目前的工作中，研究了湍流标量通量的更高级模型对污染物扩散的影响。选择了两个不同的风洞实验，即二维（2D）街道峡谷和三维（3D）市区模型，以验证模型的性能。在商业软件FLUENT 6.3中总共实现了五个各向异性代数通量模型和两个第二矩模型。使用所有这些模型以及简单的梯度扩散模型（具有不同的Schmidt湍流数），并将结果与​​使用统计性能指标的测量结果进行比较，以评估其预测能力。与实验相比，所有评估的模型都显示出良好的总体一致性。在二维模拟中，各向异性模型比各向同性模型提供更好的浓度预测。但是，这些改进在3D模拟中很小，通常消失了。最后，提出并讨论了基于模型系数敏感性分析，数值和实验模型局限性以及与模拟无源标量污染扩散相关的其他参数和假设的建模改进。

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    Izarra Garcia Rafael;

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  • 年度 2011
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  • 正文语种 eng
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