时变来流下城市街谷内空气流动与污染物扩散数值模拟

Air ventilation and pollutant/energy dispersion in urban street canyons could be promoted by reasonable urban planning and building layout design, which will finally improve the atmospheric environment in urban areas. Revealing the influencing mechanism of building layout on air flow and pollutant/energy dispersion characteristics in non-uniform street canyons under time series incoming wind conditions is the necessary theoretical preparation to implement rational urban planning and building layout design. Based on the large eddy simulation and an universal sub-grid eddy viscosity model, a numerical model will be established for the micro-scale environment simulation. Air flow and pollutant dispersion in non-uniform street canyons under time series in coming wind conditions will be investigated, to reveal the influencing mechanisms of building layout design such as building heights, relative position and area occupation ratio on air flow and pollutant dispersion in urban street canyons. The involved techniques such as the implementation methods of time series boundary conditions, constructing the non-uniform urban street canyon model, and the evaluation methods on intermittent air flow and pollutant dispersion in urban street canyons will be investigated. Theoretical basis and technical support for urban planning and building layout design will be provided to improve the air quality in urban street canyons. The current project has theoretical significance and application value for urban atmospheric environment modeling and urban planning and design.

通过合理的城市规划和建筑布局设计，可以促进城市街谷内通风和污染/热物质扩散，改善城市街谷内大气环境。揭示实时变化的来流条件下非均匀街谷内空气流动与污染/热物质扩散规律及建筑布局影响机制，是进行合理的城市规划和建筑布局设计必须的理论准备。本项目以城市街谷微尺度环境为研究对象，结合物理建模和数值模拟方法，构建非均匀街谷模型，研究时变来流边界条件的实施方法，基于大涡模拟通用亚格子模式建立时变来流下非均匀街谷微尺度环境数值模拟系统；研究时变来流下非均匀街谷内空气流动与污染物扩散规律及评价方法，揭示街谷两侧建筑高度、相对位置、高低建筑物占地比例等因素对城市街谷内空气流动及污染物扩散的影响机制,为通过合理的城市规划和建筑布局设计改善城市大气环境提供理论依据和技术支持。本项目研究成果对城市规划设计和城市大气环境模拟有重要理论意义和应用价值。

本项目以城市街谷微环境为研究对象，结合物理建模和数值模拟方法，构建非均匀街谷模型，研究时变来流边界条件的实施方法，基于湍流的大涡模拟方法建立时变来流及非均匀街谷模型下微尺度大气环境数值模拟方法；研究时变来流条件及街谷非均匀性对街谷内空气流动与污染物扩散的影响规律及评价方法。. 本项目研究得到以下主要结论及成果：. （1）基于建筑屋顶观测的高频率风场数据，利用滑移平均、分段平均等方法分析数据显示，城市边界层实际风场的变化类型有渐变式和台阶式，以渐变式为主；取30s或1min周期进行分段平均所得风速序列折线与滑移平均结果非常接近，对街谷内外空气交换效率的计算结果相差不大；当取3min为平均周期得到风速序列值时，其折线只能大概反映真实来流的变化情况，对街谷内外空气交换效率的计算结果与1min为平均周期时相比，减小20%-30%；综合考虑，以3分钟左右为周期进行分段平均较为合理，而变化过程可采用渐变式。. （2）形成了一套对邻近建筑具体刻画、对远邻区域以多孔介质模型描述的非均匀街谷模型构建方法；建筑非均匀布局与变化的来流条件都能引起街谷内外空气的宏观对流，大大促进街谷内污染物向外扩散。. （3）对街谷内空气流动及污染物扩散效率的评价可以通过行人高度平均污染物浓度与分布、建筑顶部截面空气交换律及污染物交换律等统计结果为参考。. 本项目研究成果有望在城市微环境模拟中得到推广应用，为更好的进行科学合理的城市规划设计提供参考。