Shaping buildings to promote street ventilation: A large-eddy simulation study

Proper ventilation of urban streets is important for safeguarding the health and comfort of urban inhabitants. To compare the influence of different street canyon building geometries on urban ventilation, large-eddy simulations (LES) have been performed under neutral stability conditions. Five different street canyon building geometries have been tested: the i) flat roof, ii) pitched roof, iii) round roof, iv) terraced building and v) building with balconies. The geometries were configured as seven building arrays, with six street canyons in between them aligned in the span-wise direction. The Air Exchange Rate (ACH) between the street canyons and the free atmosphere has been computed for the different cases. The results show that the ACH is very sensitive to the building geometry; therefore, it appears reasonable to suggest that buildings can be shaped to promote urban ventilation. The paper also proposes an alternative ACH estimation method based on the folded-normal distribution that is shown to produce very good estimates of the LES-computed ACH. The new method uses vertical mean velocity and turbulence statistics that can be obtained from less intensive Computational Fluid Dynamic (CFD) models. A simplified two-reservoir Pollutant Concentration (PC) estimation methodology based on the ACH results is also proposed.