界面密度对城市街道自然通风和污染扩散影响的数值模拟

Computational Fluid Dynamics Simulation of the Influence of Street Interface Density on Natural Ventilation and Pollutants Diffusion in Urban Streets

在完全过渡到绿色交通之前,由高密度建设和车辆尾气排放直接引起的城市街道空气污染问题是城市大气污染治理的一个重要议题。针对城市街道设计管控中界面密度这一重要形态参数,构建典型城市街道空气流动和污染扩散的三维数值模型,利用计算流体力学模拟方法研究界面密度对城市街道自然通风和空气质量的影响,并评估不同界面密度下城市街道自然通风性能和污染扩散能力。研究表明,街道任意一侧界面密度降低,整体上均有利于城市街道自然通风性能和污染扩散能力的提升,而相比街道下游,上游界面密度降低对街道通风环境和空气质量的改善效果更为显著;建筑布局形式对不同界面密度下城市街道整体空气流动和污染扩散的影响具有临界效应,该临界的上游界面密度约为0.8;相比对称式布局,采用错列式布局更有利于提升街道自然通风性能和污染扩散能力,从而促进街道空间空气流通和环境品质改善。

Objectives Prior to the advent of low-carbon travel,the air pollution arising from vehicle exhaust emissions within the urban canopy layer has remained a significant challenge in the governance of urban atmospheric environments.Methods This paper presents a series of three-dimensional physical models representing typical urban streets,with varying street interface density(SID).The models employ the computational fluid dynamics(CFD)simulations to assess the impact of SID on airflow patterns and pollutant dispersion.Metrics such as air exchange rate,purging flow rate,average residence time,and pollutant concentration in pedestrian areas are utilized to evaluate the natural ventilation performance and pollutant diffusion capacity across urban streets with different SIDs.Results The findings illustrate that the CFD simulation approach is an effective means of elucidating the intricate details of airflow and pollutant dispersion within urban street spaces.A reduction in SID on both sides of urban streets has been demonstrated to enhance natural ventilation and air quality.Notably,a decrease in the upstream SID has a more pronounced effect on improving air quality compared to that of the downstream.The arrangement of buildings adjacent to urban streets significantly impacts the overall ventilation performance and pollutant dispersion capacity under different SIDs,with a critical upstream SID value of approximately 0.8.Conclusions The proposed CFD simulation method can facilitate a comprehensive understanding of airflow and pollutant dispersal mechanisms,thereby enabling more scientific planning and design control of urban street spaces.Furthermore,it helps to provide proactive strategies for residents residing near urban streets to cope with traffic-related air pollution risks.