Numerical Simulation Of Micro-environ-ment In Urban Resident Sub-district

With the development of China's economy, accelerating the urbanization process, improved people's environmental protection consciousness and healthy and comfortable concept, micro-environment problems of urban resident sub-districts have attracted more and more attention. Micro-environment within the resident sub-districts includes the wind environment, pollution environment, thermal environment, light environment and acoustic environment, ect. In this paper, numerical simulation of micro-environmental flow,pollutant dispersion,thermal environment in a real resident sub-districts of Hangzhou was carried out, made a series of important conclusions, providing definite reference for housing planning and design, avoiding the aggregation of outdoor pollutants and improving the outdoor thermal environment.Firstly, RANS (Reynolds-Averaged Navier-stokes) simulation of summer typical wind environment in the resident sub-district was carried out. The results show that a large and tall building in the upstream region of the resident sub-district is adverse to the ventilation in summer. Although a large open region near the ground is beneficial to the wind environment, making the flow more fluently, it can influences evidently on the surrounding flows. Moreover, the distribution of streamwise velocity behind the upwind building follows a Gaussian-like distribution, whereas it deviates from the normal distribution in the downstream region.Secondly, author used the LES (Large Eddy Simulation) to simulate the process of dispersion of automobile exhaust in the resident sub-district. The results show that a large and tall building in the upstream neighboring region of the pollution source is disadvantageous to the streamwise dispersion of automobile exhaust, causing pollutants gather a great in the leeward side of large and tall building, but it can accelerates the spread of pollutants along the height direction. Complex distribution of buildings in the resident sub-district determines the complexity of the dispersion of pollutants. Spatial distribution of buildings near the pollution source obvious influences on the dispersion of pollutants. Unreasonable Spatial distribution of buildings can lead to pollutants gather a great around the buildings that close to the pollution source, resulting in wicked pollution environment. Furthermore, maximum root mean square (RMS) concentration of pollutants is not always appear in a position that is most close to the pollution source, which may occurs in the downstream neighboring region of the pollution source.Finally, RANS (Reynolds-Averaged Navier-stokes) simulation of outdoor thermal environment in the resident sub-district was carried out. In the calculation process, the author have performed coupled simulation of convection (convection heat transfer between air and building surfaces or the ground), radiation including solar radiation, radiation heat transfer between building surfaces or between the ground and building surfaces and conduction only considering one-dimensional building wall heat conduction and neglecting heat conduction in the ground to evaluate the outdoor thermal environment. The results show that solar radiation including solar altitude and the value of the solar radiation and spatial distribution of buildings in the resident sub-districts, which can influence on the building shading,radiation heat transfer between building surfaces and micro-environmental flow in the resident sub-districts, are the most important factors in the outdoor thermal environment of the resident sub-district. Relative to the ground covered interlocking blocks, the ground covered grass makes the decrease of outdoor air temperature (other condition are the same). Pave the grass in the upstream of windward building is the best measure to cooling. Large areas of grass can make the air temperature fluctuations gentler.