Modeling of Air Pollutant Dispersion in Street Canyons in Cross-Wind

Abstract

A study of vehicle exhaust dispersion within different street canyons models in an urban ventilated by cross-wind is conducted at this work to investigate how pollution dispersion is affected by wind speed, building height to width ratios, street and building geometries, and canyon street number. For all cases, cars exhaust was represented by a line source emitting CO2 and pollution dispersion was studied in two and three dimensions, airflow and the street canyons were assumed thermally isolated. The FLUENT Computational Fluid Dynamics (CFD) software package has been used with a standard k-e, RNG k-e and sstk-ω turbulence models to simulate different street canyon models. For all models, theresults show a vortex appearance within the street canyon, with updrafts near the upwind buildings and down-draft near the downwind buildings. In the transverse vertical plane at mid-canyon show that the pollutant concentrations has higher concentrations at the leeward face than that at the windward faces, and has higher concentrations above downwindbuildings than that above upwind buildings, Longitudinal distributions of pollutant concentrations at leeward and windward faces show decreasing of the concentration with increasing building height. For multi-street models, the pollutant concentrations increase for higher order street in wind direction. The pollutant concentration results were compared withMeroney et al. [9] experiments. Also a series of flow visualization and static pressure coefficient measurements were performed in the smoke tunnel and wind tunnel to compared with the numerical study.