Abstract
A wind tunnel study of the flow and diffusion within model urban canopies was conducted. In the Part 1 of the stidy, the mean flow and turbulence structure within and above canopies were investigated. The model canopies consisted of the cubes of 8 cm high in a diamond array, and the plan-area densitiy of the cubes was changed from 10% to 40%. Streamwise and vertical velocity components were measured with a split fiber probe designed for measuring flow velocity in those regions of highly turbulent and reversing fl ows. Three different types of flow patterns were identified through cross-sections of mean velocity vectors, and transitions between them were determined by the density of cubes. The three flow patterns can be referred to as isolated roughness flow, wake interference flow, and skimming flow, following the nomenclature of Morris (1955, Trans. A. S. M. E., 120, 373-398). As the density of cubes increases, streamwise velocityes within the canopy decay until they reach zero at the case of ρz=40%, and streamwise velocity fluctuations due to flow separation on the roof disappear for the cases of ρz>20%.
