Numerical Simulation Study Of The Wind Environment For Urban Roads Along River Based On Porous Medium Model

At present, researches on environmental problem resulted from urban traffic focus mainly on the countermeasures for pollution source control, traffic reduce, fuel renewal and exhaust treatment, etc., considering the whole city as objective. In 2002, Wang GuangTao, Minister of Ministry of Construction P.R.China pointed out that traffic capacity and environment capacity should be considered together. Researches on environment optimization and pollution control through adjusting building density, height and optimizing urban road construction is still at the stage of exploring. Analysis of the wind environment with numerical simulation has not been reported. This paper systematically simulated numerical the wind environment for urban roads along river based on Porous Medium Model and pointed out theory and methods of harmonizing criterion, harmonizing model and quantitative analysis related to sustainable plan of urban roads.The full paper was divided into five chapters. The main research contents are displayed as following:(l)Because of the great amount of calculation resulted from complexity of buildings besides urban roads, buildings and roads were parameterizedly treated as porous medium with momentum conflux under extended design conditions. Outer combination software was developed based on network division combined with logarithmic outline distribution of the wind speed of atmospheric boundary layers. The numerical simulation model for the wind environment for urban roads along river was set up.(2) Compared to the limitation of the previous researches only on pollution source control and fuel renewal. This paper analyzedsystematically and quantitatively the wind environment for urban roads along river, regarding the wind environment for urban roads along river and the other parameters, such as, construction of urban traffic, adjustment of city layout, airflow, radiological intensity, building groups and pollution sources etc. as a dynamic system.(3) Through repeated calculation with the above numerical simulation model, numerical simulation results of the wind environment for urban roads along river were abtracted, which reflect the different flow speed, flow direction, building height, building density, pollutant density and road arrangement, etc. in different plans; and a set of calculation method was established. Through figure and cartoon image, etc., the calculation results can directly show air temperature, wind speed and harmful gas distribution, etc. of urban roads along river in X city to customers and provide clear conclusion and scientific guide for nonprofessional personnel. Speed fields, temperature fields, dissipation rate distribution, turbulent energy distribution and concentration fields obtained from the simulation show:?Pollutant diffusion of urban roads along river was enhanced with the increase of traffic density.?Diffusion rate of the automobile exhaust near the ground under the high wind speed is obviously faster than that under the low wind speed.(DWhen the wind direction keeps same with the road direction (the main urban streets and the wind direct are parallel), the exhaust diffusion was enhanced, and the pollution concentration reduced, but pollutants accumulated down to the wind direction, leading to serious excess of the pollutant concentration beyond standards in some areas. When the wind direction and the street direction are vertical, the part pollutant diffusion is obviously improved and thepartly excess of the pollutant concentration beyond standards cannot easily be formed, but the influence on buildings along the street becomes greater. In addition, when the angle between the wind direction and the street direction presents between 0 and 90°, the pollutant concentrations on the road result from the effect of parallel wind and vertical wind together (but are not the simple superposition). So under the influence of complicated landform and buildings in cities, the automobile exhaust emission cannot be calculated by the projection principle.?Height of buildings influences pollutant diffusion remarkably. The variation tendency of pollutant concentration reduces with the increase of the height of buildings. With the building height of 6-10 m, the pollution concentration variation amounts to about 8%; when the building height varies from 10 m to 20 m, the pollution concentration changes more greatly, about 24%. Because high buildings in urban lead to extreme disadvantageous diffusion conditions for automobile exhaust, the pollutant emission by urban roads must be strictly controlled. When the concentration of harmful pollutants exceeds the air environment standards, the traffic density will be limited, which maybe forms the "soft bottleneck" of the environment pollution. The planning and management of urban traffic is very important, and should be further investigated.(D Building density influences the pollution diffusion obviously. The pollutant concentration increases with the increase of the building density. With the height of 6 m, the maximum pollutant concentration increases by 10.6% with the increase of building density from 40% to 60%, and by 26.6% with the increase of building density from 20% to 60%. With the other heights the situation is similar.?Analysis on diffusion of different pollutants shows that the pollutant concentration in every position presents linear change with variation of the pollution source intensity. The pollutant concentration was analyzed with the different road width. With widening of roads, the pollutant concentration increase with the same pollution source intensity; and the pollutant concentration decrease with the same total pollution amount.The simulation results accord with the general physical law, showing this numerical method is correct.(4) Comparison between results of the flow field tested in wind tunnel and numerical simulation results shows that results of speed field and dissipation rate field accord well with each other; but there is relatively large difference in turbulent energy field, which does not influence the whole numerical simulation results significantly. The correctness of the physical model of the wind environment for urban roads along river was further proved.The numerical simulation of the wind environment for urban roads along river based on porous media model can provide the design base for controlling the building height and density, etc., the feasible guarantee for overall arrangement of building and roads, the basis for developing one set of the software package for analyzing the wind environment for urban roads along river. Hopefully, the understanding of the wind environment change for urban roads along river will be enhanced. The research will contribute to the sustainable development of the economy and society.