Dispersion from elevated sources above obstacle arrays: modelling requirements

A series of wind-tunnel experiments is used to investigate the requirements of 'practical' models for the prediction of the behaviour of stack emissio ns from an industrial site (i.e. a group of buildings), in particular for t he determination of ground-level concentration or exposure downwind from th e site. The study addresses Gaussian plume modelling and, assuming that an adequate model exists for treating the emission in the absence of complicat ing site features, considers the questions: a) How should the model be modified to account for the influence of the sit e? b) Which of these modifications is most important? c) How can a group of site buildings be replaced by an 'effective' building ? Realistic modelling of plume height reduction (building induced downwash) i s shown to be the key to the successful prediction of the dispersion of ele vated emissions above obstacle arrays tin this case, for WH greater than or equal to 1.2, where h is the source height and H the building height). Som e simple rules are defined for representing an array by an effective obstac le.