Spatially averaged flow within obstacle arrays

Knowledge of the flow velocity within an array of buildings is important in modelling the dispersion of urban air pollution. In this paper a spatially averaged model is derived for U-C, the characteristic in-canopy velocity. The model's predictions are compared with experimental results from various sources. The model predicts the in-canopy velocity for a broad range of building packing densities (0.01 < lambda(f) < 0.44). An alternative form of the model is proposed for sparse arrays (lambda(f) < 0.2). A model is also derived for the exchange velocity U-E between the in-canopy and above-canopy flows. This model for U-E has the correct variation with packing density and gives predictions of the right order but has yet to be directly validated. (C) 2003 Elsevier Science Ltd. All rights reserved.