CFD validation study with large-eddy simulation for the dissipation of surface heat in urban canyons

Urban heat island (UHI) effects have garnered significant attention as anthropogenic factors alter local surface temperatures and air convection within urban areas. The outdoor thermal environment in urban canyons is notably influenced by surface heating, including heat dissipation from air conditioning units during operation, which has not yet been thoroughly studied. This study employs experimental data from wind tunnel tests to validate the Large-Eddy Simulation (LES) method in assessing the aerodynamic and thermal effects within urban canyons. The study first conducted LES validation for a street canyon with an aspect ratio of one, where the incoming wind direction was perpendicular to the canyon's long axis. To validate the aerodynamic and thermal effects under non-isothermal conditions, the results from LES simulations, including airflow patterns and temperature distributions, were compared with wind tunnel measurements. The agreement between the two datasets demonstrated that the LES model effectively captures the heat transfer processes within the canyon environment. Additionally, a grid sensitivity study was conducted to evaluate the influence of grid resolution. By comparing velocity and temperature distributions at different positions along seven vertical lines within the street canyon, the optimal grid resolution was determined for subsequent studies on the thermal environment of a typical neighbourhood in Hong Kong.