Wen, H; Malki-Epshtein, L; (2014) Modelling air flow and pollutant distribution inside street canyons with different roof shapes. In: Proceedings of the Building Simulation and Optimization Conference (BSO14). IBPSA-England and CIBSE: London, UK.

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Abstract

This study uses Computational Fluid Dynamics (CFD) modelling to test the effect of roof shape on airflow and air pollution in and around street canyons. Street canyons are established as a primary factor in poor roadside air quality as they inhibit ventilation of the streets, and the importance of urban street canyon design in maintaining good air quality should not be underestimated (Moussiopoulos, 2003). The streets are modelled in ANSYS FLUENT, choosing a typical scaled-down street configuration found in several experimental studies (Meroney et al., 1996, Wen et al., 2013). The entire flow domain is simplified into a two-dimensional domain with six buildings to represent five continuous street canyons. The aspect ratio is fixed as 1.25, in which we expect a large vortex to form in the center of the street canyon (Karra, 2012). The roof shapes of these six buildings are set to various structures that are typically found in London. Compared to the wellstudied simple case of symmetrical street canyons, where the buildings have continuous flat roofs and are modelled as simplified rectangular blocks, all other different roof shapes have resulted in different flow patterns and pollutant distributions within the street. These small-scale changes to roof pitch and size affect the shape of the vortex inside the canyon, and affect the overall ventilation of the street even under similar atmospheric flows. It is found that this can have a profound effect on the pollutant concentration field, with some cases leading to poor ventilation and reduced flushing of contaminants outwards of the street. The different roof shapes and geometries will be presented and their effect on pollution removal will be discussed.

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