The Study Of Pollutant Dispersion In Street Canyon Based On The Computational Fluid Dynamics And PIV

With the speeding up of urbanization and industrialization in our country, the number of motor vehicle grows rapidly in cities in recent years and pollutants motor vehicle emits have become the main source of air pollution in cities. To save the land resources in the process of urbanization, high-rise building has become a major choice of city construction and the increasing of the high-rise building can form a lot of street canyons, whose impact on the urban environment is becoming severer and severer so that a large number of harmful gas the motor vehicle emits accumulates in the street canyon and is not easy to spread out, making the residents exposure to high concentrations of pollutants motor vehicle emits in their daily travel. At the same time the pollutants will have a serious effect on indoor air quality of frontage buildings, which seriously endangers the physical and mental health of urban residents. As a result the research on diffusion law of pollutants motor vehicle emits and the building indoor and outdoor air quality has very important practical significance. Based on the atmospheric environment, traffic planning, fluid mechanics, numerical analysis and urban planning, architectural design and other discipline knowledge, the article uses numerical simulation method to study diffusion regularity and distribution of motor vehicle emissions in the urban street canyon, which provides scientific basis for rational distribution of the city’s streets and planning and construction of city street and is very important to improve the life quality of urban citizens, realize the sustainable development of cities and transportationThe research object of this article is three parallel street canyons, it is three parallel roads of Jinan city accordingly in practice. They are the east liberation road, he ping road and the east culture road respectively. Gas velocity distribution characteristic and the pollutant concentration distribution characteristics are researched under four different wind speed when the condition is that flow is in vertical direction of the length of the street. And five different wind direction, the isolated type street canyon gas flow field characteristics of pollution source intensity was also simulated change and building height on both sides different influence on gas diffusion, according to the flow field characteristics summed up the street canyon pollutant diffusion.This article uses the method of combining the numerical simulation and wind tunnel experiments and pollutant diffusion law and concentration distribution characteristics in the street canyon are comprehensively summed up.The influence factors of pollutant diffusion in the street canyon are comprehensively analyzed, including intensity of pollution sources and its distance to the structure, wind speed, wind direction, wind speed and wind direction synergy, the type of the street canyon, solar radiation, the pedestrian corridors, and other factors. The mathematical model of pollutant transport in urban street canyon is established, including control of fluid flow continuity equation, momentum equation, k-ξ equation and pollutant diffusion equation. Gas flow field and pollutants concentration distribution are simulated by the method of numerical simulation and compared with wind tunnel experimental results, the accuracy of numerical simulation is verified.Through the analysis of numerical simulation results of pollutant diffusion rule in the street canyon, when coming flow is perpendicular to the street and no matter there are obstacles in the streets or not, there is a clockwise vortex in the street canyon which brings pollutants to the leeward side. As a result, pollutant concentration on the leeward side is always higher than the windward. The nearer to the downwind, the higher pollutant concentration on the leeward side is, the same as pollutant concentration on the windward side. As wind speed increases, pollutants concentration on the leeward side and on the windward side decreases, but pollutant concentration on the leeward side is always higher than the windward side. At the same time, the impact which the wind direction, pollution sources strong, relative height on both sides of the building have on contaminant distribution in the street canyon is also simulated.The test bench of flow field measurement in the street canyon is established. Particle image velocimetry (PIV) technique was applied to wind tunnel experiment to measure the flow field in the street canyon. How several parameters of PIV system influence the measurement of the flow field is analyzed. When coming flow is perpendicular to the street, two-dimensional flow field in the street canyon is tested fully and the numerous experimental data is obtained.In this paper, the research provides theoretical basis for motor vehicle emission pollutants in urban street canyon area control, the control of traffic flow, the rational distribution of urban streets and city planning and construction of the street and monitoring, prevention and evaluation of atmospheric pollution.