MEASUREMENTS OF TRAFFIC-INDUCED TURBULENCE WITHIN A STREET CANYON DURING THE NANTES'99 EXPERIMENT

摘要

A full scale experiment has been performed in a street canyon, the Rue de Strasbourg in Nantes (France). This campaign, the Nantes'99 experiment, provided a detailed data base documenting, amongst others, the production of turbulent kinetic energy (TKE) by vehicles within the street. Airflow and CO concentration measurements have been analysed during days with low wind perpendicular to the street axis, i.e. for conditions expected to greatly favour the enhancement of the turbulence produced by traffic on flow and dispersion within the street canyon. It is shown that traffic is associated with an increase in turbulent kinetic energy at the lowest levels of the street, especially at the leeward side of the street. It is suggested that turbulent kinetic energy increases with the number of vehicles up to a threshold value and then decreases when vehicles form a 'block' shape that limits the additional production of turbulence. Moreover, it is suggested that traffic-produced turbulence affects pollutant dispersion reducing CO concentration at the lower levels of the leeward side of the street from a threshold value of TKE equal to about 0.15 m~2 · s~(-2). On the other hand, high traffic density generates less turbulence which in turn leads to a lower pollutant dispersion.