Passive enhancement of air flow at pedestrian level in built environments

Abstract

A densely built environment has low wind speed at the pedestrian level due to flow obstruction induced by buildings. Urban street canyons, the outdoor spaces formed between buildings, often have much lower wind speed than the atmospheric wind above the roof level. In tropical regions, wind plays an important role to improve outdoor thermal comfort of urban inhabitants by increasing the convective heat transfer from body surfaces. This thesis explores four types of passive architectural interventions to boost pedestrian-level wind speed in urban street canyons, namely void decks (open ground level), the wind catcher, the reversed wind catcher, and step-up/ step-down canyons. The proposed interventions were first studied experimentally in a recirculating water channel, where an atmospheric flow across an array of two-dimensional canyons was simulated with reduced-scale models of buildings.

The velocity profiles in the third to sixth canyons were measured with Acoustic Doppler Velocimetry. Compared with the reference case, void decks enhance near-ground flows in all measured canyons by up to a factor of two, but the enhancement effect weakens in downstream canyons. The wind catcher enhances the flow in the target canyon by 2.5 times with no significant effect in other canyons. The reversed wind catcher and the step-up/ step-down canyons reduce flows in the downstream canyons. The experimental data was used to validate computational fluid dynamics (CFD) models. CFD simulation results agree well with the experimental results for all cases. The validated CFD models were then used to study the void decks and the wind catcher in three-dimensional canyons. Void decks double near-ground flows in all canyons. The wind catcher increases near-ground flow in the target canyon by only 50% due to leakage at the sides.

An improved wind catcher with sidewalls (to prevent leakage) triples near-ground flow in the target canyon. These findings prove the potential of void decks and the wind catchers as effective architectural interventions to enhance pedestrian-level wind speed and serve as a benchmark for future work to optimize the design of void decks and wind catchers.