Large eddy simulation of flow field and pollutant diffusion around buildings with different thermal stratifications

The main aim of the current article is to explore the influence of buildings on flow field structure in the surrounding area and analyze the dispersion of pollutants using the large eddy simulation (LES) model with varying Richardson numbers (Rib). The research findings indicate that the LES model effectively replicates the effect of buildings on flow field structures and pollutant dispersion, closely aligning with wind tunnel experiments (WTE) results. The impact of various Ribvalues on the flow field structure is not immediately evident within recirculation zone on building sheltered (x/H<1.0). However, the impact of thermal stratification becomes more pronounced farther downwind. In the Rib range of 0.22–0.47, significant changes occur in the vortex center position and length of the cavity region, with Rib=0.3 exhibiting a maximum cavity length of approximately 1.9 H, suggesting a potential critical Rib between 0.22 and 0.3. As Rib increases, the energy fluctuation in the high-frequency range rises, while low-frequency energy fluctuation remains comparatively smaller. Moreover, higher Rib values lead to increased pollutant concentration near the ground on building downwind side, making it more prone to pollutant accumulation at ground level.