Evaluation of rare velocity at a pedestrian level due to turbulence in a neutrally stable shear flow over simplified urban arrays

• Published in: Journal of wind engineering and industrial aerodynamics Vol. 171; pp. 137 - 147
• Main Authors: Ikegaya, N., Ikeda, Y., Hagishima, A., Tanimoto, J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2017
• Subjects: Large-eddy simulation; Pedestrian level; Percentile wind speed; Probability density function; Simplified urban canopy; Percentile wind speed; Probability density function; Pedestrian level; Large-eddy simulation; Simplified urban canopy
• ISSN: 0167-6105; 1872-8197
• DOI: 10.1016/j.jweia.2017.10.002

The geometric dependency of the wind environment at a pedestrian level is an important issue that influences human comfort and safety in urban outdoor spaces. As such, this paper proposes to investigate the statistical features of wind speeds at the pedestrian level by calculating wind speed probability density functions based on flow field data from large-eddy simulations of simplified urban arrays, aiming to clarify the effects of urban geometry on rare velocity events such as strong gusts or extremely weak air flow. Though strong wind events occur infrequently, a positive correlation was demonstrated between percentile and mean wind speeds, indicating that the risk of gusty events increases with the increase of mean wind speeds. Conversely, the frequency of weak wind events shows an inverse correlation with mean wind speeds, showing that better ventilated urban arrays will retain higher wind speeds. Furthermore, these percentiles and occurrence frequencies are clearly expressed by the frontal area indices of urban block arrays. These results imply a trade-off between the following two objectives for urban area wind environments characterized by the urban geometry: enhancing air ventilation in urban areas and preventing strong wind gust events at a pedestrian level. • •Probability density functions of wind speed are compared for simplified arrays.• •Percentile wind speeds are proportional to the mean wind speed.• •Weak wind speed occurrences decrease with increases in the mean wind speed.• •Geometric dependency of the wind environment is revealed.