Estimation of aerodynamic parameters of urban building arrays using wind tunnel measurements

The aim of this study is the experimental determination of a centre height of moment of drag force H_c, which is assumed to coincide with displacement height d on the basis of Jackson's theory. The authors performed a series of wind tunnel experiments on the spatial distribution of pressure drag acting on walls of rectangular block arrays arranged in staggered, square, and diamond layouts under the conditions of different roughness packing densities, i.e., 7.7%, 17.4%, 30.9%, and 39.1%. Total drag and wind profile of the arrays were preliminarily measured by a floating drag balance and a hot-wire anemometer, and roughness length z_o and d were derived using two-parameter fitting in our previous work. H_c values determined by the pressure drag measurement were compared with d of our previous work. The results show that the estimated H_c values for staggered and square arrays are significantly smaller than d except for the data of lowest packing density. Moreover, the z_o values estimated using one-parameter fitting and measured H_c are slightly larger than those of previous work for the three arrays with high packing density. Although inconsistencies of H_c and d exist, it is likely that H_c could be explained as d for a range of low packing densities, i.e., below 30.9%. The present results suggest the necessity of both more accurate data of spatially averaged wind profile and direct measurement of H_c for experimental determination of the roughness length and displacement height of a block array.