The aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment. Three aerodynamic parameters characterising arraysthe drag coefficient (C d ), roughness length (z o ) and displacement height (d)-are used for analysis. C d is based on the direct measurement of the total surface shear using a floating element, and the other two parameters are estimated by logarithmic fitting of the measured wind profile and predetermined total drag force. The configurations of 63 arrays used for measurement were designed to estimate the effects of layout, wind direction and the height variability of the blocks on these parameters for various roughness packing densities. The results are summarised as follows: (1) The estimated C d and z o of the staggered arrays peak against the plan area index (λ p ) and frontal area index (λ f ), in contrast with values for the square arrays, which are less sensitive to λ p and λ f . In addition, the square arrays with a wind direction of 45 • have a considerably larger C d , and the wind direction increases z o /H by up to a factor of 2. (2) The effect of the non-uniformity of roughness height on z o is more remarkable when λ f exceeds 20%, and the discrepancy in z o is particularly remarkable and exceeds 200%. (3) The effect of the layout of tall blocks on C d is stronger than that of short blocks. These results indicate that the effects of both wind direction and the non-uniformity of the heights of buildings on urban aerodynamic parameters vary greatly with λ p and λ f ; hence, these effects should be taken into account by considering the roughness packing density.
A simple urban energy balance model for mesoscale simulations (SUMM) was tested using results from an outdoor scale-model experiment. The model geometry is assumed to be an infinitely extended regular array of uniform buildings, each of which is composed of six faces (roof, floor, and four vertical walls). The SUMM explicitly considers the three dimensionality of surface geometry and theoretically predicts the energy balance at each face without time-consuming iterations. The SUMM was compared with outdoor scale-model experiments. The simulated energy balance and surface temperatures agree well with the values measured on a reduced-scale hardware model corresponding to the numerical model geometry.
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