2D PIV Measurements of Street Canyon Flow for Buildings with Varying Angles and Separation Distances

The study of the flow within a street canyon has myriads of practical applications and requires an understanding of the physical flow mechanisms that govern the air / pollutant transport. While previous street canyon measurements have focused on two dimensional canyons or parallel three dimensional street canyons, many real world cities have buildings aligned at different angles to the approaching boundary layer. For this work, experiments were performed in a 7.9 m long boundary layer wind tunnel facility with a working cross section of 0.61 m × 0.91 m and at a free stream velocity of ~ 7 m / s. The turbulent boundary layer was generated using Lego's having a roughness height of ~ 2mm, while the buildings were simulated using 32mm cubes. 2D PIV was used for the experiment to acquire velocity statistics along various planes.

The observations indicate that having the upwind building at an angle to the incoming boundary layer (with the downwind building remaining normal) significantly modifies the flow field typically associated with a traditional two dimensional street canyon. As the angle of the upwind building is increased from 0 to 45 degrees, the momentum flux down into the canyon is significantly enhanced near the downwind building. It is also observed that increasing the angle of the upwind building modifies the flow in the wake, with the vortex core markedly shifting towards the downwind building as the angle of the upwind building increases from 0 to 45 degrees. Such mean wind observations along with turbulence observations made by varying the distances and angles of the buildings are presented in the paper.