CFD analysis of building separations in street canyons

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CFD analysis of building separations in street canyons

 

Author: Yeung, Chi-ho
Title: CFD analysis of building separations in street canyons
Degree: M.Eng.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Pollutants -- Analysis
Computational fluid dynamics
Department: Dept. of Building Services Engineering
Pages: viii, 96 leaves : ill. ; 31 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2356388
URI: http://theses.lib.polyu.edu.hk/handle/200/5806
Abstract: This thesis is devoted to the study of flow and pollutant dispersion characteristics in a three-dimensional urban street canyon for various building separations. The building separation to the building frontal width ratio (S/FW) and the locations of building separations were investigated using a FLUENT code computational fluid dynamics (CFD) model. Flow and dispersion of gaseous pollutants were modeled using the standard k-ε turbulence model, which was solved numerically based on the Reynolds- average Navier-Strokes (RANS) equations. The concentration fields in the urban canyons with building height to street width ratios (aspect ratio) of 1, 2 and 5 were examined together with three S/FW ratios of 10%, 20% and 30%. The locations of the building separations either on upwind building or downwind building were further investigated in CFD model. Vehicle emissions were simulated as a single line source along the street. The numerical model has been validated with the results obtain from a wind tunnel model. The results obtained indicate that the building separations are not effective in pollutant dispersion in all the examined street canyon configurations, The wind flow is affected by the aspect ratios. In a street canyon having an aspect ratio of 1, increasing separations from 10% to 20% gives 80% average pollutant reduction in reference points at 2m above the ground. In a street canyon having an aspect ratio of 2, average pollutant in reference points at 2m above the ground has a gradual reduction for increasing building separations. In a street canyon having high aspect ratios, thick stationary layers of pollutant were formed at the bottom parts of the street where the wind availability does not create enough dispersion effects. These simulation results provide valuable insights in assessment, planning and implementation of building separations to create a sustainable environment in side urban street canyons.

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