Evaluating the effects of envelope features on the pollutant distribution and ventilation performance by CFD simulations and scaled outdoor experiments

Previous studies on the effects of envelope features on ventilation performance have neglected the buoyancy effect or simplified it as a uniform surface heating effect. However, envelope features can create a shading effect that changes the temperature distribution and enhances the buoyancy effect, thus resulting in inaccurate findings. We conducted computational fluid dynamics (CFD) simulations based on scaled outdoor experiments to investigate the effects of different envelope features (balconies, overhangs, and wing walls) on pollutant dispersion and ventilation performance. The buoyancy effect created a new local vortex and changed the wind flow pattern at the base of the flat-facade and wing wall street canyons. The age of the air at the base of the flat-facade, balcony, overhang, and wing wall street canyons increased by 30.23 %, 20.45 %, 21.74 %, and 30.95 %, respectively. Moreover, when investigating the effects of envelope features on ventilation performance while ignoring the buoyancy effect, there was a high error rate in the ventilation performance, and the rates were as follows: wing wall (24.03 %) > flat-facade (23.20 %) > overhang (18.56 %) > balcony (14.05 %). This study provides a suitable methodology for investigating the effects of different envelope features on pollutant dispersion and ventilation performance in two-dimensional street canyons.