Computational formulation for the evaluation of street canyon ventilation and pollutant removal performance
Computational formulation for the evaluation of street canyon ventilation and pollutant removal performance
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DOI：
10.1016/j.atmosenv.2008.09.045
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发表时间：
2008-12
影响因子：
5
通讯作者：
W. Cheng;Chun-Ho Liu;D. Leung
中科院分区：
文献类型：
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作者：
W. Cheng;Chun-Ho Liu;D. Leung
提出了一种基于空气交换率（ACH）、污染物交换率（PCH）、平均污染物浓度（Θ）和污染物滞留时间（τ）的街道峡谷通风和污染物去除性能的计算公式。使用计算流体动力学（CFD），新开发的配方适用于二维（2D）理想化的街道峡谷与不同的建筑物高度街道宽度（纵横比）。采用雷诺平均的Navier-Stokes（RANS）方程和重整化群（RNG）k− ε湍流模型。在考虑污染物守恒的情况下，比较了一阶迎风、二阶迎风和三阶单调上游中心守恒律格式（MUSCL）的精度.结果表明，一阶迎风方程由于其过度耗散的特性，对污染物输运的计算精度不够，而二阶迎风方程和三阶MUSCL方程的计算误差约为10%。ACH和PCH被分解为平均和湍流分量，其中屋顶层输送过程主要由湍流分量控制。垂直风速和污染物通量的空间分布也进行了研究，以探讨街道峡谷的通风和污染物去除机制。
A computational formulation using the concept of air exchange rate (ACH), pollutant exchange rate (PCH), average pollutant concentration (Θ) and pollutant retention time (τ) is proposed to evaluate the ventilation and pollutant removal performance of street canyons. Using computational fluid dynamics (CFD), the newly developed formulation is applied to two-dimensional (2D) idealized street canyons with different building-height-to-street-width (aspect) ratios. The Reynolds-averaged Navier-Stokes (RANS) equations equipped with the Renormalization Group (RNG) k−ɛ turbulence model is adopted. The accuracy of three numerical discretizations, including the 1st-order upwind, 2nd-order upwind and 3rd-order monotone upstream-centered schemes for conservation laws (MUSCL), are compared by considering the pollutant conservation. It is found that the 1st-order upwind is not accurate enough for the pollutant transport mainly due to its over dissipative nature while the 2nd-order upwind and 3rd-order MUSCL exhibit an error of 10%. The ACH and PCH are decomposed into the mean and turbulent components in which the roof-level transport processes are dominated by the turbulent component. The spatial distributions of the vertical wind velocity and pollutant flux are also investigated to examine the ventilation and pollutant removal mechanisms of street canyons.