Pedestrian-level Air Flow and Ventilation around Adjacent Buildings in Step-up Configuration

Abstract

The outdoor air ventilation impact of a taller building at a downwind location in a layout of two adjacent buildings in different step-up configurations is presented in this paper. The criteria for ventilation assessment adopted are dimensionless parameters called velocity ratio (VR) and air ventilation rate (AER), and the parameters examined are the separation distance (WV) between the buildings and the ratio of height of downwind building to that of upwind building, herein referred to as building height ratio (HR). A three-dimensional (3-D) numerical simulation employing the Computational Fluid Dynamics (CFD) technique based on Reynolds-Averaged Navier-Stokes (RANS) equation and Realizable k-ε turbulence model was used to study the turbulent flow field around various full-scale size configurations of the adjacent buildings. Results show that while VR generally increases with height ratio, it increases with separation distance until a certain maximum distance which depends on the height ratio. AER on the other hand generally increases with height ratio, but decreases with separation distance. The results indicate that greater air motion is induced at the pedestrian level as the height of the downwind building increases, and greater rate of air flow is exchanged between the buildings cavity and the surroundings. Based on the VR results obtained for the building configurations examined, a separation distance of between 18 m and 30 m is proposed for configurations 2.0 ≤HR≤ 3.0, and between 18 m and 24 m for configurations HR = 1.0 and 1.5, to maximally invigorate the pedestrian-level air flow.