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

Abstract

Cities suffer from low wind speeds due to the blockage effects of urban structures. Low wind speeds inhibit a city's ability to self-ventilate and reduce thermal comfort in tropical cities. Building porosity has been shown to be an effective architectural feature to channel winds into the pedestrian level. However, previous studies have focused on building porosity in single buildings or two-dimensional urban street canyons. We extended the investigations of building porosity to three-dimensional urban street canyons with computational fluid dynamics simulations. Validated numerical models were used to conduct parametric studies on void decks (empty spaces at the ground floors). By allowing winds to flow through them, void decks can enhance pedestrian-level wind speeds by more than twofold compared to the reference case without void decks. The wind enhancement effect is the strongest at the first canyon and decreases downstream. The effectiveness of a void deck is greatly improved by increasing the void deck height. The average wind speed in the first canyon increases from 13 percent to 59 percent (of the freestream wind speed) by increasing the void deck height from 2 m to 6 m. On the other hand, the building height and canyon (height-to-width) aspect ratio have a much smaller influence on void-deck effectiveness. Non-uniform building height in an array of buildings also has a minor influence on the effectiveness. Therefore, void decks are equally effective to enhance pedestrian-level wind speeds in urban areas with tall buildings and buildings with non-uniform height. Keywords: Void ground floor; Building porosity; CFD simulation; Wind field modification; Non-uniform building height