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The Effect of Urban Geometries and Roof Shapes on Airflow and Pollutant Dispersion: A CFD Investigation

Wen, H; (2017) The Effect of Urban Geometries and Roof Shapes on Airflow and Pollutant Dispersion: A CFD Investigation. Doctoral thesis , UCL (University College London). Green open access

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Abstract

Street canyons, where long narrow streets are bordered by a continuous row of buildings on both sides, are a typical urban geometry which leads to problems of high pollution and heat accumulation. With the trend of modernization and urbanization, it is inevitable to have more street canyons and those will become deeper. This compels scholars to research detailed building designs and urban planning, in order to mitigate the problems of street canyons. This thesis uses Computational Fluid Dynamics (CFD) to study the impacts of several urban geometries on ventilation and pollutant removal, including pitched roofs, surrounding tall buildings, heterogeneous buildings and T-junctions. Before carrying out the study, benchmarking is performed to determine optimal CFD settings and to guarantee model accuracy. The impacts of pitched roofs are studied separately through a parametric approach. In general, the pitched roofs produce similar flow patterns compared to the flat roofs, but they reduce velocity and turbulence and increase pollutant concentration in the street. Moreover, it should be noted that high pitch rise and pitched roof(s) on the leeward building are two designs that are likely to cause even higher pollutant concentrations in the street and at pedestrian level. The area around Gloucester Place, London, is selected to be modelled in detail, in order to investigate the impacts of other typical urban geometries on airflow and pollutant dispersion. It is found that the downstream tall building and the T-junction between the windward buildings have profound impacts. The tall building produces along-street flow that does not normally form in consecutive homogenous street canyons, leading to significant improvement in ventilation and pollutant removal. This finding implies the great potential of isolated tall buildings to improve local air quality. The T-junction weakens the ventilation around it by breaking vortex flow. For this reason, the position of T-junctions should be carefully designed to avoid any unexpected pollution hot-spots.

Type: Thesis (Doctoral)
Title: The Effect of Urban Geometries and Roof Shapes on Airflow and Pollutant Dispersion: A CFD Investigation
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Keywords: CFD, street canyon, airflow, pollutant dispersion, pitched roofs, tall building, T-junction
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Civil, Environ and Geomatic Eng
URI: https://discovery.ucl.ac.uk/id/eprint/1547519
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