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ABSTRACT: A study was carried out by using the numerical simulation method to obtain the total concentration of a specific objective street canyon for different layouts with the different aspect ratio of Hd/Hu (windward-building-height-to-leeward-building-height) under a specific street width. It is shown that the concentration distributions and the total concentration values are strongly dependent on the number and rotating direction of vortices within and out of the street canyon due to the variation of geometric configurations of the street canyon. The preliminary study for the limited street canyon configuration shows that there may exist a critical aspect height ratio to make the total concentration of the specific street canyon be small. Generally the strong step-down canyon is a good layout relative to the other types. [Copyright &y& Elsevier]

Abstract: The objective of this study is to provide a simulation of emissions from vehicle exhausts in a street canyon within an urban environment. Standard, RNG and Chen–Kim – turbulence models are compared with the wind tunnel measured data for optimization of turbulence model. In the first approach, the investigation is made into the effect of the different roof shapes and ambient building structures. The results indicate that the in-canyon vortex dynamics (e.g. vortex orientation) and the characteristics of pollutant dispersion are dependent on the roof shapes and ambient building structures strongly. A second set of calculations for a three-dimensional simulation of the street canyon setup was performed to investigate the influence of building geometry on pollutant dispersion. The validation of the numerical model was evaluated using an extensive experimental database obtained from the atmospheric boundary layer wind tunnel at the Meteorological Institute of Hamburg University, Germany (Studie on different roof geometries in a simplified urban environment, 1995). The studies give evidence that roof shapes, the ambient building configurations and building geometries are important factors determining the flow patterns and pollutant dispersion in street canyon. [Copyright &y& Elsevier]