Numerical study of airflow pattern and pollutant dispersion in isolated buildings with various windward re-entry bays

Re-entry bays, commonly used in high-density urban environments, increase the likelihood of cross-contamination and cluster transmission among building occupants. However, systematic studies on the interaction between bays space dimensions and building height in influencing pollutant dispersion remain lacking, hindering evidence-based design optimization. This study employs computational fluid dynamics (CFD) simulations to explore the impact of various re-entry bay configurations on airflow patterns and pollutant distribution. The façade stagnation point compactly indicates regime shifts that co-govern transport with height (H) and aspect ratio (D/W). Deeper bays split a single vortex into inner–outer vortices and enlarge low-velocity zones at lower elevations. Practically, overly deep bays should be avoided–keep D/W < 2 for low-rise, < 3 for mid-rise, and < 6 for high-rise buildings. Convective flux dominates pollutant dispersion within the bays, whereas turbulent flux plays a secondary role. Elevating the emission source strengthens upward transport and dilution. Personal intake fraction (P_IF) peaks at the source but decreases strongly with increasing H and height of source (low-rise > mid-rise > high-rise), with upper-façade exposure in high-rise cases reduced by 3–4 orders of magnitude relative to mid-rise when the emission source is at low elevation. Positioning exhausts higher (e.g., above 0.8H) minimizes accumulation and health risks. These findings offer empirical insights for optimizing architectural designs, serving as a strategic tool for sustainable urban development.