A wind tunnel study of organised and turbulent air motions in urban street canyons

High concentrations of car-exhaust gases in urban street canyons are typically associated with low wind velocities or situations when the wind blows perpendicular to the canyon axis. The latter flow configuration has been studied in a wind tunnel model of a street canyon. The mean flow and turbulence structure have both been investigated and comparisons have been carried out with results of full-scale flow measurements in urban street canyons. A qualitative similarity has been found between the results of atmospheric measurements and flow characteristics in the modelled street canyon. Data from all employed sources give evidence of a flow acceleration (in some cases, rather sharp) above roof level. Additionally, the effects of traffic on the organised and turbulent components of airflow in the canyon have been quantified. The experimental data show significant differences in flow and turbulence patterns corresponding to the model cases of one-way and two-way traffic.