Modelling of pollutant dispersion in urban street canyons by means of a large-eddy simulation approach

Large-eddy simulation is used to study the flow dynamics and the concentrat ion dispersion in urban street canyons. This method is particularly used to investigate the two-dimensional characteristics of the concentration field established for flows perpendicular to the street with emissions released near the floor of the street by motor vehicles. The aim of this work is to study the influence of the instantaneous flow on the concentration field. O ur results show that, for a street that is twice as wide as it is high, the average statistical solution presents two counter-rotating whirls, in agre ement with previous experimental results. The concentration in the leeward region of the canyon, compared with the windward one, is significant when t he wind is perpendicular to the axis of the canyon.