A review of simplified numerical approaches for fast urban airflow simulation

As the urban area under study continues to expand, the high computational cost of urban wind and thermal environments simulation is becoming a major challenge for researchers. Therefore, researchers have developed several fast and simplified numerical simulation methods in recent years. This review provides a systematic overview of three methods that have been relatively well developed and applied to outdoor airflow simulation, including the Porous Media Model (PMM), Fast Fluid Dynamics (FFD) and outdoor Multizone Model (MM). The computational principles, development history, turbulence models, simulation platforms and validation methods of the three approaches are analyzed and compared, and the computational cost, problems and future development directions are discussed. In addition, some promising fast simulation methods are summarized for future outdoor applications. Based on the analysis of previous studies, PMM is the simplifications of urban geometry, while MM sets the city model as a nodal equation without using a turbulence model, and FFD speeds up the simulation by simplifying the governing equations’ solving process. Based on the analysis of previous studies, using PMM and FFD can be more than 5 and 15 times faster than using traditional CFD methods, respectively, and the use of MM models is on average 5 times faster than using Ansys Fluent and 20 times faster than using ENVI-met in a same study. Overall, designers and academics will be able to use this review as a reference for ideas and methods to reduce computational costs when simulating urban-scale airflow in the future.