Simulation of gaseous pollutant dispersion around an isolated building using the k-ω SST (shear stress transport) turbulence model

The dispersion of gaseous pollutant around buildings is complex due to complex turbulence features such as flow detachment and zones of high shear. Computational fluid dynamics (CFD) models are one of the most promising tools to describe the pollutant distribution in the near field of buildings. Reynolds-averaged Navier-Stokes (RANS) models are the most commonly used CFD techniques to address turbulence transport of the pollutant. This research work studies the use of k - omega SST closure model for the gas dispersion around a building by fully resolving the viscous sublayer for the first time. The performance of standard k - epsilon model is also included for comparison, along with results of an extensively validated Gaussian dispersion model, the U. S. Environmental Protection Agency (EPA) AERMOD (American Meteorological Society/U. S. Environmental Protection Agency Regulatory Model). This study's CFD models apply the standard k - epsilon and the k - omega SST turbulence models to obtain wind flow field. A passive concentration transport equation is then calculated based on the resolved flow field to simulate the distribution of pollutant concentrations. The resultant simulation of both wind flow and concentration fields are validated rigorously by extensive data using multiple validation metrics. The wind flow field can be acceptably modeled by the k - epsilon model. However, the k - epsilon model fails to simulate the gas dispersion. The k - omega SST model outperforms k - omega in both flow and dispersion simulations, with higher hit rates for dimensionless velocity components and higher " factor of 2" of observations (FAC2) for normalized concentration. All these validation metrics of k - omega SST model pass the quality assurance criteria recommended by The Association of German Engineers (Verein Deutscher Ingenieure, VDI) guideline. Furthermore, these metrics are better than or the same as those in the literature. Comparison between the performances of k - omega. SST and AERMOD shows that the CFD simulation is superior to Gaussian-type model for pollutant dispersion in the near wake of obstacles. AERMOD can perform as a screening tool for near-field gas dispersion due to its expeditious calculation and the ability to handle complicated cases. The utilization of k - omega. SST to simulate gaseous pollutant dispersion around an isolated building is appropriate and is expected to be suitable for complex urban environment.