Fluid modelling studies are useful to overcome some of the difficulties encountered in full-scale studies. They are attractive because essential boundary variables and the nature of the surface can be controlled and measurements can be performed with the necessary spatial resolution. The latter point is a major advantage over field studies which are often limited to single point measurements which restricts the applicability of results. The objective of this study was to investigate the spatial characteristics of the mean and turbulent flow fields close to and within the canopy of a rough surface using regularly arrayed rigid roughness elements (cubes) of varying density. The measurements were performed in the open-circuit blower wind tunnel (13.5 m long, 1.5 m wide and 1.2 m high) of the Research Institute for Applied Mechanics, Kyushu University in Fukuoka, Japan. A Laser Doppler anemometer was used to measure the turbulence within the boundary layer developed over 4 different density arrays. This instrument is superior to unmodified, conventional X-wire anemometers and in particular is able to measure under conditions of high turbulence intensity and within regions of reverse flow directions.
Results will be presented of vertical and transverse (to the flow direction) profiles of mean wind and turbulence statistics (normalized stress and standard deviations) as a function of non-dimensional height and roughness density. The roughness and density effects can be clearly seen within and up to two times the height of the canopy. In particular a re-circulating vortex is observed immediately behind individual roughness elements depending on the density of the array. The results will be compared to data from other rough-wall wind tunnel studies and urban observations where available.