A comparison of measurements and CFD model predictions for pollutant dispersion in cities.

An accurate description of car movements in an urban area is required for accurate prediction of the air pollution concentration field. A 3-D Eulerian-Lagrangian approach to moving vehicles that takes into account the traffic-induced flow field and turbulence is presented. The approach is based on Computational Fluid Dynamics (CFD) calculations using Eulerian approach to the continuous phase and Lagrangian approach to the discrete phase of moving objects-vehicles. In the first part of the present contribution, the method is applied to pollutants dispersion in a city tunnel outlet in Brno and to a street structure in Hannover, Germany. In the second part, a model of traffic dynamics inside a street intersection in the centre of Brno is presented. This model accounts for the dynamics of traffic lights and a corresponding traffic-generated flow field and emissions in different time intervals during the traffic light sequence. All results of numerical modelling are compared with field measurements with very good agreement. A commercial CFD code StarCD was used into which the Lagrangian model and traffic dynamics model were integrated.