Title: Numerical simulations of street canyon ventilation and pollutant dispersion

Authors: Chi-To Ng; Chun-Ho Liu

Addresses: Department of Mechanical Engineering, 7/F Haking Wong Building, The University of Hong Kong, Pokfulam Road, Hong Kong, China ' Department of Mechanical Engineering, 7/F Haking Wong Building, The University of Hong Kong, Pokfulam Road, Hong Kong, China

Abstract: The relationship among air exchange rate (ACH), pollutant exchange rate (PCH) and friction factor (f) is proposed in this study to evaluate the performance of ventilation and pollution removal of hypothetical urban areas. Urban areas were simplified to arrays of idealised, repeated two-dimensional (2D) street canyons of different building-height-to-street-width (aspect) ratios (ARs) and building shapes were examined with the use of computational fluid dynamics (CFD). The Reynolds-averaged Navier-Stokes (RANS) equations with the Renormalization Group (RNG) k-ε turbulence model were adopted for the CFD. It was found that the turbulent component of ACH contributes more than 60% to the ventilation performance and is linearly proportional to the square root of friction factor (ACH'' ∝ f1/2) for the building shapes tested in this study. Unlike the well-defined relationship between ACH and f, the relationship of pollutant transport (or heat transfer) against f has not yet been formulated because of the different behaviour between building shapes, aspect ratios and locations of pollutant sources.

Keywords: air quality; air pollution; computational fluid dynamics; CFD; city ventilation; pollutant transport; turbulence modelling; numerical simulation; street canyon ventilation; atmospheric dispersion modelling; air exchange rate; pollutant exchange rate; friction factor.

DOI: 10.1504/IJEP.2014.065921

International Journal of Environment and Pollution, 2014 Vol.55 No.1/2/3/4, pp.167 - 173

Available online: 29 Nov 2014 *

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