This article deals with the state-of-the-art of experimental and numerical studies carried out regarding air pollutant dispersion in urban environments. Since the simulation of the dispersion field around buildings depends strongly on the correct simulation of the wind-flow structure, the studies performed during the past years on the wind-flow field around buildings are reviewed. This work also identifies errors that can produce poor results when numerically modelling wind flow and dispersion fields around buildings in urban environments. Finally, particular attention is paid to the practical guidelines developed by researchers to establish a common methodology for verification and validation of numerical simulations and/or to assist and support the users for a better implementation of the computational fluid dynamics (CFD) approach.

The dispersion of pollutants exhausted from a building roof stack located in a tower was investigated using various types of k − turbulence models, i.e., a standard k − model, a RNG k − model and a realizable k − model, all implemented using Fluent software. In order to determine the turbulence model that best helped reproduce pollutant plume dispersion, the most critical case was considered, namely, when wind blew perpendicularly towards the upstream tower, then placing the building in its wake. When numerical results were compared to wind tunnel experiments, it was found that the realizable k − turbulence model yielded the best agreement with wind tunnel results for the lowest stack height, while for the highest stack height, the RNG k − turbulence model provided greater concordance with experimental results. The realizable k − model was the only model able to provide the correct trend for the concentration distribution in the lower region between the two buildings; however, none of the models reproduced the trend in the upper regions. The standard k − model was generally found to be inadequate for reproducing vertical concentration distribution.

The dispersion of exhausted pollutants from a building roof stack situated in the wake of a neighbouring tower has been studied using the realizable k-turbulence model and computational fluid dynamics (CFD). Two scales are considered in this work, full scale (1:1) and wind tunnel scale (1:200). Of primary interest are the distributions of the plume and of the pollutant concentrations on the building roof as well as on the leeward wall of the tower. Two stack heights and pollutant exhaust velocities have been considered to study the distribution of pollutant concentrations in the neighbourhood of the building from which the pollutant is emitted. Results are compared with measurements from field and wind tunnel experiments to estimate the accuracy of simulations.

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The dispersion of pollutants exhausted from a building roof stack located in the wake of a tower is investigated by means of the realizable k-turbulence model. Variations in stack height and pollutant exhaust velocity are considered to assess their influence on the distribution of pollutant concentrations in the neighbourhood of the emitting building. In order to determine optimum locations for freshair intakes, the worst case is considered, namely when the wind originates directly upstream of the tower and places the emitting building in its wake. Special attention is given to the evolution of the plume and distribution of pollutant concentrations on the roof and windward wall of the emitting building, as well as on the leeward wall of the upwind tower. Simulation results are compared to wind tunnel experiments conducted in a boundary layer wind tunnel. For this particular configuration, the paper shows that increasing the stack height has an effect similar to that obtained by increasing the momentum ratio, but with some differences, depending upon which wall of the two buildings is considered. On the emitting building, the leeward wall has the lowest concentration values for all stack heights and momentum ratios considered; thus this is the best location for fresh-air intakes. However, for the tower, fresh-air intakes should not be located on the leeward wall due to high pollutant concentrations. The results show completely different pollutant dispersion patterns from those for an isolated building. This highlights the importance of accounting for structures that lie in close proximity to the emitting building.