城市街道峡谷中湍流和扩散的联合PDF模拟
Joint PDF modelling of turbulent flow and dispersion in an urban street canyon
摘要：
采用新发展的粒子蒙特卡罗方法计算了城市街道峡谷中被动标量的湍流速度和浓度的联合概率密度函数。与矩闭包相比，PDF方法提供了包含所有高阶矩和相关性的基础场的完整的一点一次PDF。小规模混合的标量从一个集中的源释放在街道一级的模拟通过交换与条件均值（IECM）模型的相互作用，与微观混合时间尺度设计的几何复杂的设置。边界层沿无滑壁（建筑物侧面和顶部）是完全解决使用椭圆松弛技术，它捕获的高各向异性和不均匀性的雷諾应力张量在这些地区。本文还探讨了一种基于壁面函数的计算量较小的技术来表示边界层及其对解的影响。计算的统计数据与实验数据和大涡模拟进行了比较。目前的工作可以被认为是第一个例子的计算的完整的联合PDF的速度和运输被动标量在城市环境中。该方法被证明是成功的，在复杂的城市场景中的湍流和污染物浓度场提供高层次的统计信息。
英文摘要：
The joint probability density function (PDF) of turbulent velocity and concentration of a passive scalar in an urban street canyon is computed using a newly developed particle-in-cell Monte Carlo method. Compared to moment closures, the PDF methodology provides the full one-point one-time PDF of the underlying fields containing all higher moments and correlations. The small-scale mixing of the scalar released from a concentrated source at the street level is modelled by the interaction by exchange with the conditional mean (IECM) model, with a micro-mixing time scale designed for geometrically complex settings. The boundary layer along no-slip walls (building sides and tops) is fully resolved using an elliptic relaxation technique, which captures the high anisotropy and inhomogeneity of the Reynolds stress tensor in these regions. A less computationally intensive technique based on wall functions to represent boundary layers and its effect on the solution are also explored. The calculated statistics are compared to experimental data and large-eddy simulation. The present work can be considered as the first example of computation of the full joint PDF of velocity and a transported passive scalar in an urban setting. The methodology proves successful in providing high level statistical information on the turbulence and pollutant concentration fields in complex urban scenarios.
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