Influence of building neighbors on wind flow around a tall building

Abstract

This thesis focuses on how building neighbors influence wind flow around a tall building. The wake dynamics and flow structures around a tall building are first explored using Large Eddy Simulations (LES). Following this, wake topology, flow structures, and vortical structures are investigated when a small building is placed downstream and upstream of a tall building. The wake and flow structures formed from the building neighbors’ effects around the tall building were compared with the wake features and flow structures observed for the single tall building case. The study of the wake was first investigated when a building neighbor (small building) was present downstream of a tall building. The influence a small building has on wind flow around the tall building was investigated by examining how wake and flow structures change when a small building was introduced. A weaker downwash flow shown by the decrease in vorticity was observed as opposed to when the tall building was isolated. This is primarily due to the presence of the small building downstream which subsequently reduced the wake effects from the tall building. Pedestrians will therefore experience better comfort at the wake region as opposed to when the tall building was isolated. Different flow structures were observed. First, a reverse-c shaped type of vortex was formed at the near wake which develops into hairpin type of vortices at the far wake. When upwash, downwash, and shear layers interact, hairpin vortices form, creating an increase in wake instabilities. A horseshoe vortex forms in the wake, with its legs extending into the wake, interacting with the wake structure formed behind the buildings and having an immediate effect on wake dynamics. At the windward face of the small building, which lies in the aerodynamic wake of the tall building, the mean pressure coefficient decreased even more, reaching 𝐶𝑝 ̅̅̅ ≈ 0.07. The progressive decrease in mean pressure coefficient (82.5%) shows how the mean wind load reduces downstream due to the presence of the small building downstream. This further shows how aerodynamic wake effects decrease considerably more quickly. [...]