Large eddy simulation of thermal effect on flow field around a building model with a scale ratio of 1:1:2

Urban overheating caused by urban heat island (UHI) effect has a negative impact on energy consumption, human health and urban air quality. This interaction between the approaching and the buoyancy-driven flows significantly alters the flow patterns around the building, consequently impacting the ventilation and dispersion of pollutants in urban areas. This paper utilized large eddy simulations to investigate the effects of buoyancy flow on the flow field around an isolated cubic building with heated surfaces. Wind tunnel experiments were also conducted to validate the simulation results. Under low wind speed conditions, the study utilized Richardson numbers ( Ri) to quantify the relative contribution of forced convection and buoyancy flow. The Ri ranged from 0 to 4.00, indicating a transition in the flow field from being predominantly influenced by forced convection to being predominantly influenced by mixed convection. The windward, leeward, and all walls of the building were heated individually and compared with an isothermal building. The velocity, temperature and turbulent kinetic energy field were analysed. Significant changes in the flow field characteristics were observed under low Reynolds numbers and high surface temperatures. The thermal effects on the flow patterns led to variations in the length of the reattachment and recirculation zone.