Using CFD Software To Simulate Wind Environment And Air Pollution Dispersion In Residential Districts

Traffic emissions have been the main source of air pollutants in China as the number of vehicles is growing rapidly. A residential district consists of apartment buildings and schools. It is very close to people’s lives, especially the young and the elderly, so the air quality of a residential district is very important to people’s health. Since residential district is usually far away from industrial districts, traffic pollution is the main influencing factor of its air quality.For micro-scale air quality forecasting, field measurements as the classical way has its limitation. A method of air quality simulation that combines GIS, CFD and WRF is introduced in this paper so as to be an alternative.The wind environment and the concentration distribution of traffic pollutants of a typical residential district in Lujiazui are simulated with the CFD model. The3D model of objectives is built in AutoCAD from GIS data. Effects of simulation conditions or properties’changes are investigated, such as domain size, reproduction range of buildings, mesh resolution, wind profile index, turbulence model and differencing scheme. The way to combine CFD and the WRF model is also tested, that is to nest CFD’s grid in WRF’s and to set WRF’s results as CFD’s boundary condition. Transient simulation is used for representing time varying changes.As a conclusion, domain size effects the result to some degree. Generally, a small domain leads to a low wind speed. Reproduction range of buildings effects the result to a great extent. If the reproduction range is deduced, wind speed will increase. The reproduction of the buildings outside the target district is important as well as that inside. Buildings in a range of200-300m outside the target district should be reproduced. A mesh that is larger than5m*5m in resolution cannot feet building’s shape correctly, but a mesh that is too fine may lead to a long computing time and needs higher computer specifications. A proper mesh resolution should be set from hardware specifications and the demand for precision. There is a little difference between the PHOENICS’s and a related technical guideline’s recommended settings about wind profile index, but the difference in result is so small that is negligible. The QUICK differencing scheme can improve the result efficiently with a little increase in computing time compared to the default Hybrid scheme.