Distributions of gust and peak factors at a pedestrian level in a simplified urban canopy obtained by particle image velocimetry

Abstract

The complex velocity fields within an urban canopy affect the occurrence of rare weak and strong wind-speed phenomena at the pedestrian level. Although particle image velocimetry (PIV) is widely used to determine velocity components, it has not been applied to pedestrian spaces for rare wind events, owing to the surrounding buildings. Therefore, in this study, two velocity components within a simplified urban canopy layer were measured using time-resolved PIV by inserting a laser optics system into a focal block. We determined the turbulent statistics, probability densities, gust factor (GF), and peak factor (PF) at the pedestrian level within the canopy layer. The probability density functions of the velocity components at positions with a lower mean wind speed tend to be negatively skewed, whereas those at positions with a higher mean wind speed tend to become closer to the Gaussian distribution. The GF values are small in the regions where a larger velocity is observed. However, the PF shows less distribution than the GF, regardless of the measurement position. Owing to the importance of strong gusts, the PF could be a more useful index for evaluating strong winds speed within the urban canopy layer.