Development of a computational fluid dynamics model for pollutant dispersion in complex terrain

Abstract

This research investigated the issues of vehicular-emitted pollution in Kandy City, a valley-like environment experiencing severe air pollution problems due to a higher traffic volume, topographical aspect, and prevailing weather conditions. The COPERT emission model was used to calculate the total emission rates of 𝑁𝑂 , 𝐶𝑂, and 𝑃𝑀 in major road segments of the city. An OpenFOAM-based CFD model was developed to predict dispersion characteristics over the complex terrain, considering physical phenomena such as surface roughness, wind shear, Coriolis’s effect, surface heat flux, buoyancy effect, and turbulence. The developed model was validated against experimental results to investigate its sensitivity and efficiency, and it was found to show good agreement. 2 The developed CFD model was then applied to simulate the dispersion of vehiculargenerated air pollutants in Kandy City, considering the region’s two main wind patterns NE and SW, topography, and emission rates of major road segments. The model’s concentration and dispersion pattern of pollutants were found to vary with urban topography and wind pattern, with higher concentrations of pollutants observed in areas with high traffic volume and severe traffic congestion, such as the central business district and areas close to bus stands. The model was also used to investigate pollution dispersion patterns in 27 locations at the pedestrian level, with good agreement found between the model’s predicted concentrations of 𝑁𝑂 and experimental results. Overall, this study highlights the significance of considering topography and me- 2 teorological conditions when evaluating pollution dispersion mechanisms in urban environments. The developed CFD model can be used as a promising tool for predicting pollutant transport and wind flow in the built environment, aiding in proper urban planning to reduce pollution accumulation in significant locations. This research can contribute towards effective policies and interventions to mitigate the impacts of vehicular-generated air pollution in valley cities.