Numerical Simulation of Pollutant Dispersion in Idealized Urban Arrays across Different Thermal Conditions

This study utilizes the k-ε model to investigate the effects of complex urban structures on surrounding airflow and pollutant dispersion under different Richardson numbers (Rib). The wind tunnel experimental data used for model validation were obtained from an open-source dataset provided by the Architectural Institute of Japan (AIJ). The results demonstrate that numerical simulation effectively captures the effects of idealized urban arrays on airflow patterns and pollutant dispersion. The simulation results are consistent with those obtained from wind tunnel experiments (WTE) performed under similar conditions, thereby validating the numerical approach. The longitudinal velocity (u/uH) shows significant variation near the center of street canyons. Moreover, changes in u/uH are more pronounced on the leeward side (LS) of the building compared to the windward side (WS). When Rib exceeds 0.25, the stagnation point and vortex center on the WS of the buildings gradually move upward. Meanwhile, the vortex within the street canyons near the center of the block starts to dissipate. The length of the recirculation zone on the LS of the block decreases from x/H=15.0 to x/H=13.0, whereas the longitudinal influence range of the block expands from y/H=±9.0 to y/H=±12.0. The highest normalized turbulence kinetic energy (TKE/uH2) is observed at the WS corner of the building and diminishes as the Rib increases. Under stable stratification, increasing Rib suppresses vertical pollutant transport while enhancing horizontal spreading. Consequently, the height of high-concentration areas gradually decreases, causing pollutant accumulation within the neighborhoods and hindering pollutant dispersion.