CFD simulation of flow fields and pollutant dispersion around a cubic building considering the effect of plume buoyancies

Plume buoyancy is one of the most crucial driving forces of gas pollutant dispersion in weak wind regions such as the recirculation region. In this study, steady Reynolds-averaged Navier-Stokes (SRANS) simulation and large eddy simulation (LES) are conducted simultaneously to investigate the flow and concentration fields around a cubic building, in which the positive and negative buoyancies produced by the density difference between pollutants and the ambient air are considered at the same time. The performances of SRANS and LES are quantitatively evaluated by comparing the simulated results with the data from wind tunnel tests. In general, LES provides more accurate predictions for the time-averaged concentration fields, especially for the cases of neutral gas and heavy gas. Also, by studying the effect of different plume buoyant forces, the research finds that the increased vertical turbulent flux of light gas in the recirculation region behind the building enhances the dilution of pollutant. However, the heavy gas has an adverse effect. It is also found that the positive plume buoyancy raises the concentration fluctuation above the pollutant source considerably, while the negative plume buoyancy has a certain inhibitory effect on it. ∙ The effect of positive and negative plume buoyancy is investigated simultaneously. ∙The prediction accuracy of RANS and LES for buoyant gas dispersion is evaluated. ∙Negative buoyancy restrains the dilution of pollutants in wake region. ∙Positive buoyancy raises the concentration fluctuation behind the building.