Large-eddy simulation study on the effect of vehicle-induced turbulence and exhaust fumes on wind flow and pollutant dispersion in urban street canyons

城市化和公路运输的增加是造成城市环境中空气污染和相关健康影响的主要因素。在机动车密度高的地方，由于建筑物的存在，污染物的扩散减少。其直接后果是，空气污染水平往往超过国家空气质量限值。此外，交通引起的湍流被确定为污染物扩散的关键因素。然而，扩散模型表现出较差的性能条件下，交通引起的湍流被认为是一个主要的过程中的污染物的扩散。拟议的项目旨在更好地了解城市环境中污染物扩散所涉及的主要过程。 因此，拟议项目的主要目标是通过高分辨率的湍流分辨大涡模拟的车辆引起的湍流和废气对城市街道峡谷中的污染物的风流和运输的影响进行评估。新的方法，将明确移动车辆的复杂几何形状进行测试和验证，在第一步对现有的风洞数据。在第二步中，将对经典街道峡谷设置进行一套全面的模拟，以评估车辆引起的湍流对风流的影响以及对单个汽车排气中污染物释放的分散性的影响。模拟将侧重于理想化的设置，但包括峡谷内植被的影响，如路边树木和树篱，差热街道和建筑物墙壁，以及它们的综合影响，以评估车辆引起的影响的重要性。这套通用的模拟将由参数研究加以补充，例如考虑到平均风向和风速以及不同的交通密度和车队组成。最后，现有的参数化车辆引起的影响将审查在拟议的项目中创建的广泛的数据集和一个新的参数化，适合大涡模拟模型将在第一个案例研究进行测试。

Increased urbanization and road transport are major factors contributing to air pollution and associated health effects in urban environments. On local scale, where motor vehicle density is high, pollutant dispersion is reduced due the presence of buildings. As a direct consequence, air pollution levels often exceed national air quality limit values. Also, traffic-induced turbulence is identified to be a key factor for the dispersion of pollutants. However, dispersion models show poor performance under conditions, where traffic-induced turbulence is considered to be a major process for the dispersion of pollutants. The proposed project aims at acquiring a better knowledge about the principal processes involved when it comes to the dispersion of pollutants in urban environments. The main objective of the proposed project is thus the evaluation of the effect of vehicle-induced turbulence and exhaust fumes on the wind flow and transport of pollutants in urban street canyons by means of high-resolution turbulence-resolving large-eddy simulations. Novel methods to incorporate explicitly moving vehicles of complex geometry will be tested and validated in a first step against existing wind tunnel data. In a second step, a comprehensive set of simulations will be conducted for the classic street canyon setup to evaluate the effect of vehicle-induced turbulence on the wind flow and on the dispersion of pollutants releases from exhausts of the individual cars. The simulations will focus on idealized setups, but include the effects of in-canyon vegetation such as roadside trees and hedges, differentially-heated steets and building walls, as well their combined effect to evaluate the importants of vehicle-induced effects. This general set of simulations will be complemented by parameter studies where, e.g. the mean wind direction and speed as well as different traffic densities and fleet compositions are taking into account. Finally, existing parameterizations for vehicle-induced effects will be reviewed in the light of the extensive data set created in the proposed project and a new parameterization that is suited for large-eddy simulation models will be tested in a first case study.