Urban roughness modelling in relation to pollutant dispersion

An analytical model for the evaluation of the roughness length zO and the displacement height zd of regular building groups is presented. It suggests that apart from the frontal density (ratio of building frontal area and ground surface), the streamwise building length and the building lay-out pattern are important parameters. Experimental data for the validation have been gathered from an extensive literature study, and they have been checked against experimental requirements pointed out in this paper. The overall agreement is reasonably good, but the problems in obtaining reliable experimental zO and zd data are so large that a definitive judgement, and thereby a full model optimisation, could not be made. Possible applications of this work are roughness mapping of towns, optimisation of street design with respect to air ventilation, and optimisation and tuning of wind tunnel approach flow roughness.