Numerical Simulation On PM2.5Dispersion In Street Canyons

With the rapid development of society and the improvement of people’s quality of life, more and more people pay close attention to the quality of the air. And, vehicle emissions of pollutants in the city has become the main source of air pollution in some major cities. Where the harm of PM2.5to human health is the most. Due to city planning and land issue,coupled with more and more people flock to the city,Brought into a piece of tall buildings.the microclimate different from the atmospheric boundary layer is formed in the middle of the tall buildings. This will also affect the transmission and diffusion of pollutants. It also forced us to study the law of convection and diffusion of PM2.5.the object of this paper is a certain street canyon in Jinan, it also describes the geometry of object, flow field characteristics and pollutants convection-diffusion characteristics in street canyon and basic theory. PM2.5convective diffusion process in the streets is relatively complex and affected by many factors, mainly include:climatic conditions, wind speed, wind direction, air temperature, blocks geographical factors and sources of pollution intensity.This article employs the combination of numerical simulation and wind tunnel experiments, First of all,according to the distribution of the selected street canyon roads and buildings, establish the physical model of the appropriate size,using Gambit software to mesh, select the reasonable boundary conditions,combined with Jinan urban atmospheric boundary layer wind profile curves,define the initial speed. Select k-epsilon model and the discrete phase model, iterative simulation by Fluent software, and finally get the street canyons PM2.5convection diffusion law.Obtained from the numerical simulation of PM2.5convection-diffusion distribution pattern can be seen:(1) the same wind direction,the greater the wind speed the more intense convection-diffusion of pollutants;(2) with the same wind speed,the tetragonal always flow, pollutants accumulate in down wind in the streets of the along wind, and in north-south streets, leeward surface contaminants easily gathered.Tilt to the wind direction,spread of the local pollutants significantly strengthened, it is not easy to cause that local pollutant concentration is too high.Through the wind tunnel experiment to the flow of pollutants convection diffusion law of in north-south streets. And wind tunnel experimental results and numerical calculation results were compared and found consistent results between the two, which proves the correctness of this paper, the mathematical model and the value calculated.The content of this study for the city street planning and construction, building height and density control, vehicle exhaust emission control and traffic control to provide a scientific basis.