The pressure field within the canopy of urban-like roughness

Urban areas affect the development of atmospheric boundary layers. The tendency is to characterize their effect based on density parameters, which are closely related to the effective roughness height and the zero-plane displacement. Standard morphological models successfully predict the nonlinear behaviour of these quantities, but are insensitive to the variability of the roughness height. In this context, we investigated the flow over two surfaces: a staggered array of cubes with uniform height, and a staggered array of cuboids with random height distribution but identical packing densities. Extensive measurements of the flow field were acquired using 2D-PIV from which pressure was reconstructed. This enabled estimating the magnitude and location of the streamwise forces acting on individual roughness obstacles. To assess the viability of this method, the pressure distribution and the estimated friction velocity U_τ were compared against reported wind tunnel data and numerical simulations. The centre of pressure and magnitude of the load applied on a an arbitrary obstacle appear to be primarily dictated by the relative height of its upstream neighbor. The existence of a functional form for the normalised pressure distribution within the canopy will be addressed in this talk.