Effects of envelope features on building surface temperature and ventilation performance in 2D street canyons

The focus of previous research on urban ventilation has primarily been on flat-facade buildings. However, envelope features can affect the surface temperature and ventilation performance. We conducted an outdoor scaled experiment to investigate the impact of different envelope features on the thermal and wind environment in street canyons. The envelope features effectively reduce the surface temperature, with the impact order being as follows: overhangs > wing walls > balconies. The dimensionless parameter B is used to assess the impacts of momentum and buoyancy on urban ventilation. In a wide canyon, when B < B_c (the critical value of different envelope feature cases), the momentum dominates urban airflow. The B_c values of the flat-façade, balcony, overhang, and wing wall were 0.335, 1.084, 1.320, and 1.529, respectively, while the normalized horizontal velocities (U_0.25H/U_2H) of the flat-façade, balcony, overhang, and wing wall street canyons remained relatively constant (i.e., 0.66, 0.54, 0.62, and 0.57, respectively). When B > B_c, under the combined influence of momentum and buoyancy, U_0.25H/U_2H increases nonlinearly with B. Moreover, street canyons with envelope features exhibit a smaller B_c value than flat-facade canyons. These findings provide valuable insights into the effects of envelope features on thermal environments and urban ventilation.