Study On Urban Wind Environment And Pollutant Diffusion Based On LES Model

With the rapid development of urbanization process,the density of urban buildings is increasing,the layout of buildings is complex,showing the characteristics of tall and dense,which makes the underlying surface of the city become more rough,leading to the reduction of urban wind speed,the difficulty of pollutant diffusion,or the "Canyon effect" between tall buildings.The problems caused by urban wind environment,such as air pollution,urban heat island effect,canyon effect,are more and more prominent.Therefore,it is of great theoretical and practical significance to study the urban wind environment.In this thesis,through CFD numerical simulation,wind tunnel test and other methods,the pollution diffusion of urban wind environment is studied systematically.First of all,a three-dimensional finite element model is established for staggered joint buildings.The wind environment characteristics of staggered joint buildings are determined by wind tunnel test.The inflow wind profile and turbulence profile are fitted by the test data,and the secondary development is taken as the entry boundary condition of numerical simulation.In order to ensure the accuracy of the numerical simulation,the mesh of the numerical simulation model is analyzed,and finally the flow field characteristics and distribution patterns of staggered building groups are obtained.Secondly,by adding pollution sources in the building complex area and considering the common conditions of various pollution sources in the city,the thesis analyzes various influencing factors of pollutant diffusion,including:changes in the release height of pollution sources,changes in the release distance of pollution sources,temperature change of building surface,the change of turbulent kinetic energy at the entrance,the influence of different gas groups on pollutant diffusion.Finally,according to the physical model of the actual urban area(baoshuwan area of Xiamen City),all buildings in the area within two kilometers are modeled,and the overall wind environment and pollutant diffusion distribution in the area are studied by using the large eddy simulation.Combined with the research results of typhoon moranti,the causes of severe damage of typhoon moranti in baoshuwan area are studied.The results show that when the wind tunnel test is used as the boundary condition of the numerical simulation entrance,the velocity of the numerical wind field in the atmospheric boundary layer environment decreases gradually due to the occlusion effect of the front row buildings,only considering the velocity wind profile as the inflow condition,the result deviation is large.If the turbulence profile and the velocity wind profile are considered at the same time,the maximum deviation of the measurement point velocity is only 8%.The influence of concentration gradient on pollutant diffusion is far less than that of turbulence.The change of pollutant release height in front of the wind mainly affects pollutant diffusion by changing the flow field and turbulence state;The farther away the pollutant discharge outlet is from the building complex,the more obvious it is affected by the turbulence,the more fully developed the wake,and the greater the impact of the pollutant will be;The higher the temperature is,the greater the accumulation degree of pollutants on the building surface is;When the pollutant is located in front of the building,the larger the Schmitt number,the lower the diffusion efficiency of the pollutant,the less the probability of entering the building complex,and the lower the accumulation degree;The higher the relative molecular weight of the gas,the lower the efficiency of the turbulent transport process,which is easy to cause the accumulation of pollutants,and the longer the time required for pollutants to be purified by the wind environment.The main reason for the damage of glass curtain wall in baoshuwan area is the excessive pressure difference around the building caused by typhoon,and the accumulation degree of pollutants in this area is relatively serious under the positive west wind direction angle...