Outdoor wind speed enhancement in residential precincts in tropical cities

Abstract

Wind speeds in urban areas are significantly reduced due to the blockage effects of urban structures. Lower wind speeds inhibit passive ventilation and reduce thermal comfort in tropical cities. This thesis uses both experimental and computational fluid dynamics (CFD) modeling to explore the potential of building porosity to increase wind speeds at the pedestrian level. The computational models are first validated with experiments to justify the exclusion of thermal effects, as the models over-predict the thermal effects on heated surfaces. Validated computational simulations show that void decks can increase pedestrian-level wind speeds by more than twofold in two-dimensional urban street canyons. In three-dimensional urban street canyons, void decks not only increase the wind speeds in the street canyons, but also along the streets. The effectiveness of void decks to increase wind speed is significantly influenced by the height of void decks but not the building height. Next, the heat wave in April 2016 in Singapore is simulated with the Weather Research and Forecasting model to identify two residential precincts with high temperatures for detailed case studies. Both selected precincts are simulated with CFD models to obtain the pedestrian-level wind fields. The effects of void decks in these two real urban areas are evaluated by comparing the wind field with void decks to that in the control case without void decks. The first precinct with smooth upwind areas shows significant wind speed enhancement up to 80% of the freestream wind speed (the wind speed above the roof level) with void decks. The second precinct with rough upwind areas shows wind speed enhancement up to 50% of the freestream wind. In conclusion, void decks are an effective architectural intervention to enhance pedestrian-level wind speeds, but the effectiveness is influenced by the upwind conditions.