Influence Of Spatial Layout Of Urban Street Valley On Pollutant Diffusion

With the rapid development of China's economy and the improvement of people's quality of life,some people have become more concentrate on personal health,which cause more attention to air quality issues.However,with the rapid development of urbanization in China,more farmer pouring into the city,As a result,a lot of high-rise appear in the city,more and more cars go at express speed in the streets and lanes,of course motor vehicles constantly emit exhaust gases.However,the geometric shape of buildings formed by high-rise buildings-the influence of street valley on air circulation,which leads to the aggravation of urban pollutant emission,but it can't be well expanded Scattered,thus silting up in the corner of a city,which cause trouble to local residents' life and health.The research on the flow field and pollutant diffusion law in urban street valley has certain guiding significance for urban plan.Firstly,it introduce spatial layout of the research object,the flow field in the street valley and the theory of pollutant convection and diffusion.There are many factors that affect the convection and diffusion process of pollutants(CO)in the street valley.Here are the main factors: building layout(room skirt,distance between upstream block building and leeward side building,distance between buildings in both sides and Street Valley),the speed of wind,the angle of wind direction,temperature,radiation of solar,pollutant emission source intensity,etc.This paper use the computational fluid dynamics(CFD)method to establish the flow model of air and pollutants in urban street valley.The research mainly goes through next three aspects:(1)This paper compare the diffusion effect of pollutant molecules in the street valley which has room skirt with that in the traditional street valley,then it consider that by changing the height of room skirt.When the wind direction forms a certain Angle with the street valley,such as 45° and 90°,the pollutants in the street are silted in the leeward side.Compared with the conventional street valley,the street valley with room skirt has a better pollutant diffusion effect.With the decrease of the height of the house skirt,the pollutant molecular concentration become lower in the street valley,and the pollutants are silted in the leeward side and the exits on both sides.When the wind direction is parallel to the axis of the street valley,the variation of the skirt height has little influence on the diffusion of pollutants in the street valley.(2)This paper study the influence of wind direction on pollutant dispersion in street valley.When the Angle becomes smaller,which is formed by wind direction forms and the axis of the street valley,the deposition of pollutants becomes less in the street valley and the more conducive to the diffusion of pollutants.At the same time,9 cases with different room skirt heights were compared under the conditions of 0°,45° and 90°.I conclude that when the Angle becomes smaller,the variation that range of pollutant diffusion in street valley caused by skirt height becomes smaller.(3)On the basis of room skirt street valley,buildings are added in the upper and both sides of the street valley respectively.Adjusting the distance between buildings and the street valley,this paper analyzed the change degree of pollutant diffusion effect in the street valley under different circumstances,so as to find out the optimal distance range.For the upstream buildings,it is suggested that the reference distance D should within the range of 35-40 m,which minimizes the impact on pollutant diffusion in the downstream valley and conforms to the maximized use of floor space.As for the distance between buildings on the same side of the street valley,the distance between buildings on one side of the street valley is about 40 m,which is more appropriate and conducive to the diffusion of pollutants in the street valley.