A numerical experiment on the characteristics of flow and pollutant dispersion using a CFD model coupled with the WRF model

The study, concerning to the effects of highly developed residential buildings on wind flow and pollutant dispersion, is examined in a built-up area of Seoul, South Korea. In predicting realistic flows in an urban area, it is very important to reflect variations of a mesoscale weather field. For this, a mesoscale numerical weather prediction model, the Weather Research and Forecasting (WRF) model is employed and coupled with a computational fluid dynamics (CFD) model. The CFD model is based on a Reynolds-averaged Navier-Stokes equations model with the renormalization group (RNG) k-e turbulence model. Initial input data sets are produced by the WRF model which can simulate mesoscale weather well to supply CFD model input values. Numerical simulations using a CFD model are carried out after proper interpolation of data sets produced by the WRF model in time and space. All the simulations are performed via a one-way nesting method. The WRF model is simulated for 30 hours starting from 18 UTC 6 August 2009 using NCEP final analysis data as initial and boundary conditions. During the period, a high-pressure system was dominant, clear condition, is maintained, and synoptic winds are weak. Four nested computational domains are considered, and grid sizes of the innermost domain are 500 m. The coupled CFD-WRF model is integrated for 24 hours. Sea level pressures are well represented during the simulation period by WRF model compared with the analysis charts. The results pointed out the importance of the usage to coupled CFD-WRF model in predicting the wind speed and direction in urban areas. The CFD-WRF model predicted them well than that by the WRF model alone. It is because the CFD-WRF model considered adjacent buildings and more realistic topographies. The results also showed that tall buildings in the urban area affected the flow and pollutant dispersion much in the domain. The pollutant concentration inside the area bounded by the tall buildings is low due to the partial increase in the wind speed, that is, the channeling effect even though the area is near from the pollutant sources.