CFD Simulation On Wind Environment And Pollutant Distribution In Typical City Street Canyon

With the intensification of global urbanization,the city center is full of tall buildings,the degree of industrialization is getting higher and higher,the road traffic is becoming more and more crowded,and the number of motor vehicles is growing rapidly.Motor vehicle exhaust has become a major contributor to atmospheric pollutants.As an important factor of urban microclimate,urban wind environment has a direct impact on the diffusion of atmospheric pollutants.Therefore,it is of great practical significance to understand the characteristics of urban wind environment,study the diffusion and distribution of atmospheric pollutants in urban space and people's healthy life.This article takes the urban street canyons as the research object,starting from the street canyons geometric features and building envelope feature,Divide street canyons into short street canyons(L /W <4)and long street canyons(L /W> 8),Eight models in the short street canyons by changing the aspect ratio(L/W = 2,4)and aspect ratio(H /W = 1,2)and the different aspect ratio in the long street canyon(H /W = 1,2 3)and 12 models of different envelope feature(balcony,horizontal overhang and vertical wing wall).Computational fluid dynamics(CFD)experiments were used to explore the characteristics of the flow field and the distribution of pollutants in the facade envelope feature of typical urban street canyons and long street canyons with different aspect ratios.The main research work and results are as follows: In this paper,we draw grids,select reasonable turbulence models and boundary conditions,fluent simulation,and data analysis on 8 models of short street canyon and 12 models of long street canyon,and discuss the characteristics of street canyon flow field and pollutant distribution.It is found that in the short street canyons(L /W <4),the pollutants in the parallel street canyons are symmetrically distributed.When the height-to-width ratio(H /W)of the street canyon is small,the pollutant concentration decreases from the center to both sides;When the height-to-width ratio(H /W)of the street canyon is large,the pollutant concentration increases from the center to both sides;U-type street canyons are more likely to accumulate pollutants;In the parallel street canyons,when the aspect ratio is(H /W = 2,L /W = 4),in the U-type street canyons,the aspect ratio is(H /W = 1,2;L /W = 2),The concentration of pollutants on the windward wall will be greater than that on the leeward wall.In the Long street canyons(H /W > 8),in most cases,the concentration of pollutants on the leeward wall surface of the street canyon is greater than on the windward wall surface;The envelope feature can obviously affect the distribution of pollutants on the two walls of the street canyons;When the street canyons are wide(H /W = 1),the balcony and overhang can reduce the concentration of pollutants above 2 floors,but at this situation,the pollutants will be concentrated at the lowest position of the leeward wall;When the street canyons are narrow(H /W = 2,3),adding the balcony,overhangr,and wing wall will instead promote the ability of pollutants to climb to the higher wall of the street canyon.