Numerical study of flow pattern and pedestrian level wind comfort inside a uniform street canyon at different angles of attack

The air flow around an individual building is complex. Around two or more buildings, a recirculating flow can occur in the street canyon between them. Such urban flows can introduce high wind speeds at pedestrian level in the building wake or in the recirculating flow in the street canyon, causing discomfort or even injuries. In this paper, a fundamental study using the steady Reynolds-Averaged Navier-Stokes (RANS) approach of computational fluid dynamics (CFD) simulations has been carried out to study the effect of different flow angles of attack (AOA) on the flow pattern and pedestrian comfort inside a uniform street canyon. Analysis was performed at 0◦, 15◦, 30◦, 45◦, 60◦, 75◦ and 90◦ AOA using turbulent conditions. The Reynolds number involved in this study was 8.1 × 10⁶ based on the height of the building and free stream velocity. A street width to building height aspect ratio of S/H = 2 has been considered in this study because high spacing between buildings could be considered dangerous for pedestrian comfort. The aim of this study is to provide input into knowledge-based expert systems by providing mean wind speeds at the entire pedestrian level street width. This study reveals that at a given separated distance of buildings inside a street canyon pedestrian comfort is greater when flow approaches angles of 0◦, 15◦, 60◦ and 75◦ compared to other AOA. It also reveals that the flow structure inside a street canyon at a given aspect ratio is different to the single building case: entrainment of the surrounding fluid towards the axis of symmetry by the horseshoe vortex in the wake region of the buildings or inside the street canyon, loses symmetry.