CFD Simulations of Pedestrian Wind Comfort in an Urban Area Considering Trees' Drag Effects

This study investigated the effects of trees on the pedestrian wind comfort in the Pukyong National University (PKNU) campus. For this, we implemented the tree's drag parameterization scheme to a computational fluid dynamics (CFD) model and validated the simulated results against a field measurement and previous simulation data. In field measurements, wind speeds were weaker at the top and bottom rather than at the middle-levels in the vicinity of the trees. The wind speeds and turbulent kinetic energy (TKE) were affected at five-fold the distance of the tree height in the downwind region. The CFD model similarly reproduced the wind speeds and TKEs in the downwind region of the trees. For better reproduction of the measurement results, we additionally conducted sensitivity simulations with the varying vertical leaf area density (LAD) of trees. We applied the CFD model to investigating the trees' effects on pedestrian wind comfort in the PKNU campus in a view of wind comfort criteria based on the Beaufort wind-force scale (BWS). We performed the numerical simulations for the 16 inflow directions to investigate the comprehensive distribution of pedestrian wind comfort. Comprehensively, poor wind comforts (BWSs ≥ 4) for the 'sitting long' activity were widely occurred in the narrow spaces between buildings, around the high-rise buildings, and in the wide road and unobstructed area. The main reasons were the increase in wind speed resulted from the convergence and descent of airflows. In the tree cases, the wind speeds inside the PKNU campus were overall reduced due to the trees' drag. Resultantly, the BWSs decreased by one to three levels, improving the wind comfort inside the PKNU campus.