Air pollutant transport risk regions in U-shaped lightwells: Fast identification method on critical Richardson number

In high-rise buildings, U-shaped lightwells for natural ventilation may cause the cross-household transmission of air pollutants. In this study, a fast identification method based on the critical Richardson number (Ri) for the transport risk region (TRR) is proposed, with the coupling effects of wind and buoyant pressure considered. By correlating the concentration field of pollutant dispersion with the velocity field, a critical velocity ratio criterion (local velocity/reference velocity) for TRR generation was first established. Subsequently, using a combination of computational fluid dynamics and the proper orthogonal decomposition method, 208 wind–buoyancy coupled scenarios were simulated, revealing the Ri range of 0.31–11.82 for TRR generation. In the simulation results, all TRRs are located between the 22nd and 27th floors (the total number of stories is 32). The centre of the TRR shifts downward as Ri increases. The vertical span of the TRR first increases and then decreases with rising Ri, reaching a maximum span of approximately six stories at Ri = 5.15. The proper orthogonal decomposition method reduces computation time by 90% while maintaining accuracy (average deviation <10%).