A simplified numerical method for modelling the wind flow and ventilation at urban-scale street network

Abstract

Street networks serve as the main open corridors for wind flow within urban areas, so understanding their ventilation performance and capacity of removing pollutants helps improve urban air quality. However, conventional modelling methods using an exact building model (EBM) are hard-pressed to simulate urban-scale areas, due to their extremely high computing load. To reduce time and cost of numerical simulations, and accurately predict the flow field and ventilation within the street network, a simplified modelling approach (i.e., EBM&PMM) is proposed, in which only the first row of buildings flanking the street is modelled by EBM and the rest of the urban buildings are modelled by a porous media model (PMM). The performance of EBM&PMM is evaluated by three common modelling approaches, i.e., EBM, PMM, and sealed concrete model (SCM) in which the building complexes with gaps are treated as an enclosed entity. A typical crossing street network flanked by four communities (building arrays) is used for this study. The age of air (τP) and ventilation flux (Q) obtained from the four modelling methods are compared. The results show that EBM&PMM predicts τP and Q well, and the flow pattern by this model agrees well with EBM. PMM significantly underestimates τP but exaggerates Q in street networks, and it fails to give the detailed flow patterns. SCM over-predicts τP, and Q between the community and street is zero. Furthermore, the first row of buildings facing the street plays a decisive role in flow pattern and ventilation effectiveness of the street network.