Unsteady-state CFD simulations on the impacts of urban geometry on outdoor thermal comfort within idealized building arrays

Abstract

This study investigated outdoor thermal comfort within 5 × 5 idealized building arrays on five consecutive days by conducting unsteady computational fluid dynamic (CFD) simulations. The dynamic interacting effects of building height topology, building distance and building layout on airflow patterns, spatial distributions and spatially averaged outdoor thermal environment were evaluated by UTCI (Universal Thermal Comfort Index). CitySim Pro was used to simulate the transient solar-induced temperatures on the walls of buildings and grounds inside building arrays, which were then set as thermal boundary conditions in CFD simulations. The results showed that the influence of transient wind conditions on airflow patterns and urban thermal comfort was significant so steady simulations or unsteady simulations of one typical day might not provide a complete overview of the wind-thermal environment. The results also showed that presenting the results by average UTCI or spatial distribution could lead to different conclusions on the impacts of urban geometry on urban thermal comfort, especially the impact of building distance. Increasing the building height always provided positive effects on urban thermal comfort. The spatial distributions of UTCI in three-dimensional building arrays with equal aspect ratio diverse significantly, which was not observed in the pattern of average UTCI.