Cities near mountainous terrain, such as Hong Kong, frequently encounter topography-induced twist wind. Twist wind profile (TWP) refers to the vertical variation of wind direction, distinguishing it from conventional wind profile (CWP), and exerting a significant influence on pedestrian wind and thermal comfort. The arcade design has been extensively employed in urban areas due to its capacity for enhancing pedestrian comfort; however, a comprehensive understanding of its performance under realistic solar radiation and the twist wind effect remains elusive. The paper aims to investigate the impact of twist winds on arcade design and analyze wind and thermal comfort by varying parameters such as elevation ratios, arcade width ratios, canyon width, street length and depth ratios (L/D), and asymmetric building heights under CWP and TWP. The steady Reynold-averaged Navier-Stokes model with standard k-ε models with discrete ordinate (DO) radiation were applied. The results demonstrate that the weakened downwash flow caused by the twist wind within the street canyon was insufficient to counteract the buoyancy-driven flow generated by solar radiation. This condition facilitated the escape of heated air from the lower levels of the street canyon, especially in step-down configurations, resulting in a physiological equivalent temperature (PET) value that was on average 1–2 ℃ lower under TWP compared to CWP. Increasing the arcade width may negatively impact thermal comfort under TWP. The cooling effect of twist winds was more pronounced in shorter street canyons, with the PET increasing by 2 ℃ under CWP and by 4 ℃ under TWP as the L/D increased from 1 to 10. The wind velocity in the downstream area decreased fivefold under TWP, whereas it remained relatively stable as the L/D increased from 1 to 10 under CWP.

Pedestrian level wind environment is affected by stagnated airflow in high-density cities. This study provides an understanding of the effects of building height and porosity size on pedestrian level wind comfort. The computational fluid dynamics (CFD) technique is utilized to reproduce wind flow around buildings at pedestrian level, and new wind comfort criteria for a low wind environment are adopted to evaluate wind comfort. More specifically, the Steady Reynolds Averaged Navier–Stokes (RANS) renormalization group (RNG) k–ε turbulence model is employed in this study, and the accuracy of the simulation results are assured by validation against the wind tunnel test data. The influence of different building heights and porosity sizes on wind comfort around an isolated building and a group of buildings are subsequently examined. It is shown that an increase building height could improve wind comfort inside the site boundary for both the isolated building and group of buildings. Furthermore, the wind comfort benefits increased when porosity is on the first floor compared to when it is on the second floor. Moreover, larger porosity size generally results in better wind comfort than smaller porosity size. From a practical view point, this study provides information for city planners and architects to use in the improvement of pedestrian level wind comfort, without losing land use efficacy.