| With the development of urbanization,the scale of the city has gradually increased,environmental problems have become increasingly serious,the emissions of automobile exhaust and the smog caused by industrial production.City street valley,as the basic unit of urban life,its internal environmental quality directly affects the health of residents.In order to improve the living environment of urban residents,this topic studies the characteristics of wind fields and the diffusion of pollutants in urban street valleys.Based on(CFD)technology,using three-dimensional,steady,NS equation,k-εtwo-equation turbulence model,starting from the action mechanism of flow field around the flow,using the Fluent software,select 100010020 city street valley as the research object,analyze the street wind field The parameters of wind speed,whirl,wind direction and other parameters change,and study the relationship between urban block planning control parameters and street wind environment.Through on-site testing of a block in Bengbu City,the calculation model is optimized,and the influence of street planning parameters(aspect ratio,height to low ratio,branch distribution,roof form,etc.)on the wind environment in the valley is found,and the best design is found.The analysis of the flow field characteristics is obtained:(1)The wind direction affects the street wind field: When the wind direction is perpendicular to the city street valley,the wind speed at the corner of the street valley entrance and the street valley exit is larger,but the wind speed in the street valley is small.The ventilation is poor;parallel to the urban street valley,the air flow in the street valley is a typical channel flow,the wind speed is large,the canyon effect will be formed,and the ventilation is good.(2)As the aspect ratio α is gradually reduced,the eddy area in the urban street valley is reduced,the wind speed is increased,which is conducive to the diffusion of pollutants,and the wind environment in the valley is relatively good when the aspect ratio is 0.3<α <0.7.(3)With the gradual decrease of the height-to-low ratio β,the range of the vortex area in the valley is gradually reduced,and the wind environment inside the valley is good in fluidity and the ventilation quality is better.(4)Adding branch roads is beneficial to improve the wind environment inside the valley.With the increase of the number of branches,the high and low wind areas of the leeward surface of the street are separated,and the vortex area is reduced.The windenvironment in the street valley will be improved;Large,the wind direction in the upper and lower reaches of the street valley is consistent,and the direction of the vortex is clockwise,which is conducive to the spread of pollutants in the street valley.(5)The roof type affects the street wind field: the airflow in the “convex” roof street valley is larger than the “concave” roof,and there is a clockwise vortex in the valley,which has a large wind speed,which is conducive to the spread of pollutants;“Left Triangle” The flow velocity of the wind field in the roof street valley has increased,and the direction is upward,while the flow velocity in the windward face is large,which is conducive to the transmission and diffusion of pollutants. |
