Impact of wedge-shaped roofs on airflow and pollutant dispersion inside urban street canyons

Abstract The objective of this study is to investigate numerically the effect of wedge-shaped roofs on wind flow and pollutant dispersion in a street canyon within an urban environment. A two-dimensional computational fluid dynamics (CFD) model for evaluating airflow and pollutant dispersion within an urban street canyon is firstly developed using the FLUENT code, and then validated against the wind tunnel experiment. It was found that the model performance is satisfactory. Having established this, the wind flow and pollutant dispersion in urban street canyons of sixteen different wedge-shaped roof combinations are simulated. The computed velocity fields and concentration contours indicate that the in-canyon vortex dynamics and pollutant distriburtion are strongly dependent on the wedge-shaped roof configurations: (1) the height of a wedge-shaped roof peak is a crucial parameter determining the in-canyon vortex structure when an upward wedge-shaped roof is placed on the upwind building of a canyon; (2) both the heights of upstream and downstream corners of the upwind building have a significant impact on the in-canyon vortical flow when a downward wedge-shaped roof is placed on the upwind building of a canyon, due to flow separation as wind passes through the roof peak; (3) the height of upstream corner of the downwind building is an important factor deciding the in-canyon flow pattern when a wedge-shaped roof is placed on the downwind building of a canyon; (4) the characteristics of pollutant dispersion vary for different wedge-shaped roof configurations, and pollution levels are much higher in the “step-down” canyons relative to the “even” and “step-up” ones.

[1]  Cb Christof Gromke,et al.  Dispersion of traffic exhausts in urban street canyons with tree plantings : experimental and numerical investigations , 2007 .

[2]  Helen ApSimon,et al.  A numerical study of atmospheric pollutant dispersion in different two-dimensional street canyon configurations , 2003 .

[3]  Michael Schatzmann,et al.  Study of line source characteristics for 2-D physical modelling of pollutant dispersion in street canyons , 1996 .

[4]  W. Hung,et al.  Validation of a two-dimensional pollutant dispersion model in an isolated street canyon , 2002 .

[5]  Sandrine Anquetin,et al.  Pollutant dispersion and thermal effects in urban street canyons , 1996 .

[6]  Stylianos Rafailidis,et al.  Influence of Building Areal Density and Roof Shape on the Wind Characteristics Above a Town , 1997 .

[7]  Goodarz Ahmadi,et al.  Airflow and pollutant transport in street canyons , 2006 .

[8]  J.-F. Sini,et al.  A Wind Tunnel Investigation of the Influence of Solar-Induced Wall-Heating on the Flow Regime within a Simulated Urban Street Canyon , 2002 .

[9]  Shaodong Xie,et al.  Spatial distribution of traffic-related pollutant concentrations in street canyons , 2003 .

[10]  Erich J. Plate,et al.  Wind-tunnel study of concentration fields in street canyons , 1999 .

[11]  Janet F. Barlow,et al.  Dispersion and transfer of passive scalars in and above street canyons—Large-eddy simulations , 2008 .

[12]  Kit Ming Lam,et al.  Recent progress in CFD modelling of wind field and pollutant transport in street canyons , 2006 .

[13]  Alison S. Tomlin,et al.  Flow field measurements in the proximity of an urban intersection in London, UK , 2005 .

[14]  Bodo Ruck,et al.  Influence of trees on the dispersion of pollutants in an urban street canyon - experimental investigation of the flow and concentration field , 2007 .

[15]  Riccardo Buccolieri,et al.  Dispersion study in a street canyon with tree planting by means of wind tunnel and numerical investigations – Evaluation of CFD data with experimental data , 2008 .

[16]  Zhen Huang,et al.  Impact of building configuration on air quality in street canyon , 2005 .

[17]  M. Santamouris,et al.  Experimental study of temperature and airflow distribution inside an urban street canyon during hot summer weather conditions. Part II: Airflow analysis , 2008 .

[18]  J. Santiago,et al.  SLP-2D: A new Lagrangian particle model to simulate pollutant dispersion in street canyons , 2008 .

[19]  Bodo Ruck,et al.  On the Impact of Trees on Dispersion Processes of Traffic Emissions in Street Canyons , 2009 .