Abstract
Computational fluid dynamics (CFD) is currently used in the environmental field to simulate flow and dispersion of pollutants around buildings. However, the closure assumptions of the turbulence usually employed in CFD codes are not always physically based and adequate for all the flow regimes relating to practical applications. The starting point of this work is the performance assessment of the V2F (i.e.,v2¯ − f) model implemented in Ansys Fluent for simulating the flow field in an idealized array of two-dimensional canyons. The V2F model has been used in the past to predict low-speed and wall-bounded flows, but it has never been used to simulate airflows in urban street canyons. The numerical results are validated against experimental data collected in the water channel and compared with other turbulence models incorporated in Ansys Fluent (i.e., variations of bothk-εandk-ωmodels and the Reynolds stress model). The results show that the V2F model provides the best prediction of the flow field for two flow regimes commonly found in urban canopies. The V2F model is also employed to quantify the air-exchange rate (ACH) for a series of two-dimensional building arrangements, such as step-up and step-down configurations, having different aspect ratios and relative heights of the buildings. The results show a clear dependence of the ACH on the latter two parameters and highlight the role played by the turbulence in the exchange of air mass, particularly important for the step-down configurations, when the ventilation associated with the mean flow is generally poor.
Highlights
Review ArticleComputational fluid dynamics (CFD) Analysis of Urban Canopy Flows Employing the v2 − f (V2F) Model: Impact of Different Aspect Ratios and Relative Heights
Computational fluid dynamics (CFD) is currently used in the environmental field to simulate flow and dispersion of pollutants around buildings
Much effort has been done in recent years to analyze urban canopy flows by means of CFD, often using Reynolds-averaged Navier– Stokes (RANS) simulations of two-dimensional (2D) arrays of buildings. e interest of the scientific community for such a simplified building arrangement is justified by the fact that the 2D array can be considered as an archetype for more complex geometries [10,11,12,13]
Summary
CFD Analysis of Urban Canopy Flows Employing the V2F Model: Impact of Different Aspect Ratios and Relative Heights. Allegrini et al [17] carried out 2D steady RANS simulations with different near-wall treatments in order to validate numerical results for buoyant flows in urban street canyons by comparison with wind-tunnel measurements. Uncertainties still exist regarding the capability of CFD codes in simulating velocity and turbulence fields in different flow regimes For this reason, a comparison between numerical results obtained through Ansys Fluent v.14.5 [23] and experimental data taken in the water channel has been carried out in this work. E V2F model is employed to analyze the air-exchange rate (ACH) for a series of two-dimensional building arrangements, such as step-up and step-down configurations, having different aspect ratios and relative heights of the buildings, a design quite underexplored in the literature. The Water-Channel Experiments e numerical simulations have been validated with a series of experiments conducted in the close-loop water channel located at the Laboratory of Hydraulics of the
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