Research On The Distribution Of Air Pollutants In Various Situations In Typical Beijing Blocks Based On CFD

The problem of air pollution is highly concerned by all sectors of society,and urban air pollution has become one of the important issues affecting urban public health.Air pollutants in cities mainly come from energy,industry,housing,and transportation.With the acceleration of urbanization,energy and transportation emissions have increased sharply,and urban air pollution has become increasingly severe.Urban form refers to the spatial composition of urban entities,showing the spatial layout and appearance characteristics of the interior of the city.After pollutants are discharged into the atmosphere,the diffusion and distribution of pollutants will be affected by the urban form.Therefore,it is important to clarify the urban morphological parameters that have a significant impact on the diffusion of air pollutants and analyze the influence trend of each morphological parameter.At present,most researches on the correlation between urban form and air quality are based on the scale of urban functional areas,and the impact mechanism of urban form characteristics on the block scale on air pollution has not been accurately identified and understood.Therefore,this paper takes urban blocks as the research object,discusses the correlation between the morphological characteristics of different blocks and the distribution concentration of air pollutants,and discovers and identifies the urban morphological parameters that have a significant impact on the diffusion of air pollutants.The main research contents are as follows:（1）The study area is selected in Chaoyang District,Beijing,which are Shuanglong Nanli community represented by low-rise residential blocks,and the third phase of Zhouzhuang Jiayuan community represented by high-rise residential blocks,represented by public cluster buildings.Pingyuan Campus of Beijing University of Technology.Established a research method combining field monitoring,numerical simulation,and morphological analysis,built a block atmospheric environment monitoring system,and carried out the monitoring of pollutant mass concentrations and dynamic meteorological parameters during typical seasons.Based on ANSYS-Fluent software and C language,establish a CFD-block atmospheric environment model,perform numerical simulation on the three-dimensional spatial distribution of the block wind field and pollutants,and verify the accuracy of the simulation based on the on-site monitoring results.（2）Taking urban residential blocks as the research object,the relationship between residential block morphology and air quality（wind speed,CO,PM2.5 concentration）is discussed at the meso-scale.Through the field monitoring data and the CFD simulation results,the changes of the microclimate and the pollutant diffusion distribution in the neighborhood under different meteorological conditions are grasped.In this study,five key urban morphology parameters（building density,average building height,standard deviation of building height,average building volume,and degree of closure）were identified,which significantly changed the diffusion and distribution of atmospheric pollutants within a block.Through statistical analysis,the influence degree and action rule of each shape parameter on the atmospheric environment of the block are established.Based on this finding,the paper proposes urban morphology optimization strategies to alleviate air pollution in urban residential blocks,including reducing building enclosure,increasing building height difference and the number of independent buildings.（3）Taking urban public cluster buildings（university campuses）as the research object,this paper studies the evolution of urban morphology parameters of Pingyuanyuan Campus of Beijing University of Technology during the main development stages（2006,2008,2019）.Through CFD numerical simulation of typical weather days,the ventilation conditions and pollutant diffusion conditions in different stages of campus environment are analyzed,and the importance of morphological parameter changes in improving the ventilation conditions and pollutant dilution and diffusion in streets is explained.According to the statistical analysis results,in the evolution process of the eight morphological parameters,the six parameters,such as floor area,building density,floor area ratio,plane permeability,dispersion degree and shape coefficient,have a significant correlation trend with the "wind-pollutant" status of the block.Based on this relationship,three suggestions and principles for mitigating air pollution in the planning,design,reconstruction and extension of campus blocks are proposed,including the control of building volume and other basic parameters in the design stage,and the adjustment of building layout,permeability and geometric form in the reconstruction and extension process.