Abstract In this study, to simulate the pollution treatment as a separated phase a 3D incompressible turbulence model under isothermal conditions was considered. The hybrid RANS-LES method with a sub-grid scale(SGS) technique within the framework of two-phase flow was used to study pollution distribution in urban street canyons. An area source of pollutant with a constant concentration, located in the ground of the street canyon, was used to simulate vehicular emissions. The near-wall regions were simulated using the RANS(k-e) turbulence model and the rest of the domain was simulated with the LES model. To measure the effect of building height on pollutant dispersion, the parameter AR(Aspect Ratio) was calculated. Also to determine the effect of street width, a new parameter SWV(Street Width Value) was introduced. Governing equations were discretized using the well-known finite volume method on a staggered grid. To increase the accuracy, the second-order Van Leer Method(VLM) was applied and the Volume of Fluid(VOF) method was employed for the description of the interfaces. The Iterative line-by-line TDMA solution procedure and the Strongly Implicit Procedure(SIP) was used for the Pressure Correction Equation. A fine comparison of the results revealed that by increasing SWV, the number of vertical vortices in the canyon streets generally decreased and the vortices grew larger. In addition, increasing AR caused a rise in the pollution volume fraction in the first canyon street. The current numerical results indicate that the AR and SWV influence the flow field and volume fraction of phases inside an isolated street canyon, significantly.

中文翻译：

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使用混合 RANS-LES 方法和两相模型模拟城市街道峡谷中的污染物扩散

摘要 在这项研究中，为了将污染处理模拟为分离相，考虑了等温条件下的 3D 不可压缩湍流模型。在两相流框架内采用亚网格尺度(SGS)技术的混合RANS-LES方法研究了城市街道峡谷的污染分布。位于街道峡谷地面的具有恒定浓度的区域污染物源用于模拟车辆排放。近壁区域使用 RANS(ke) 湍流模型进行模拟，域的其余部分使用 LES 模型进行模拟。为了衡量建筑物高度对污染物扩散的影响，计算了参数 AR（纵横比）。同样为了确定街道宽度的影响，引入了一个新参数 SWV（街道宽度值）。在交错网格上使用众所周知的有限体积方法对控制方程进行离散化。为提高精度，采用二阶范里尔法（VLM）和流体体积法（VOF）描述界面。迭代逐行 TDMA 求解程序和强隐式程序 (SIP) 用于压力校正方程。结果的精细比较表明，随着SWV的增加，峡谷街道垂直涡流的数量普遍减少，涡流变大。此外，增加AR导致第一条峡谷街道的污染体积分数增加。目前的数值结果表明，AR 和 SWV 显着影响了孤立街道峡谷内相的流场和体积分数。