Downwind flow behaviours of cuboid-shaped obstacles: modelling and experiments

Abstract

Buildings or fence-like structures are frequently modelled as cuboids in simulations of environmental assessments. Understanding flows around and downwind of typical isolated buildings, in the form of cuboids, provide insightful building disposition strategies, which are particularly useful in the field of urban planning. Fast analytical models or computational numerical models are essential for sensitivity studies of various design parameters that require validation against field/experimental data. The aim of this study is to compare in detail the robustness of analytical perturbation models and the computational fluid dynamics (CFD) k − ε turbulence models for predicting the mean wake velocity defects along the centre line downwind of the cuboids, both in the near- and far-wake regions. Depending on aspect ratios of cuboids, the decay rate of maximum velocity defect behaves differently. Moreover, the CFD code over-predicts the magnitude of maximum defect in comparison with the perturbation models, whereas it over-predicts or under-predicts when compared to actual measurements. A physical explanation has been proposed in this paper. The steady CFD models, requiring less empirical input, are shown to provide satisfactory results for approximate computations of flows in the near- and far-wake regions of cuboid buildings with appropriate settings of inflow profiles and wall function.