Pedestrian-level wind speed enhancement in urban street canyons with void decks

Low wind speeds can inhibit passive ventilation and reduce thermal comfort in tropical cities. We use both experimental and numerical approaches to investigate pedestrian-level wind speed enhancement with void decks (empty spaces at the ground floors) in urban street canyons. Water channel experiments show that void decks allow wind to pass through them, thereby enhancing pedestrian-level wind speeds up to twofold. Computational fluid dynamics models validated with the experiments were used to conduct two parametric studies. The first study varied the void deck height and showed that the wind enhancement effects increase with taller void decks, as expected. The second study varied the canyon aspect ratio and showed that variations in the canyon aspect ratio had less influence on wind enhancement compared to the variations in the void deck height. This is because a void deck induces a secondary vortex, which counter-rotates with the vortex driven by the freestream. Increasing the canyon aspect ratio stretches the vortices vertically but does not alter the (normalized) flow fields. Our findings reveal the potential of void decks to channel wind into street canyons, including narrow (high height-to-width aspect ratio) canyons, which suffer from poor ventilation. The enhanced wind speeds are beneficial for pollutant dispersion and outdoor thermal comfort in tropical cities.