The evaluation of buoyancy effect on urban ventilation, especially on low wind conditions, is important for the extreme urban heat islands to improve urban climate resilience. To provide suggestions for reliable climate simulation study in the future and support the development of city-scale outdoor ventilation models, this study conducted a critical literature review on buoyancy effects on outdoor natural ventilation. First, on the neighborhood scale, this study summarized computational fluid dynamics (CFD) simulations on urban ventilation with buoyancy effects to provide suggestions on improving simulation accuracy. Suggestions on the computational mesh, turbulence models, and wall functions, as well as the realistic wall surface temperature models coupling, are provided. Furthermore, the newly emerged non-isothermal wind tunnel measurements are summarized to support future validation studies. We highlight the importance of using Large-Eddy Simulation model under weak wind and intense wind-buoyancy interaction scenarios. The Building Energy Model (BEM) is recommended to calculate the surface temperature and couple it into CFD models. Secondly, on the urban scale, in order to support the parameterization of buoyancy effect on air exchange velocity, correlations between air exchange velocity and non-dimensional parameters are explored based on existing simulation results. A linear correlation is found between the street canyon buoyancy parameter and air exchange velocity improvement. This review suggests that the current database of air exchange velocity is sparse and limited at a narrow range of buoyancy intensity and urban densities, and thus emphasizes the need for future studies on strong buoyancy and weak wind conditions.
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