Turbulent boundary layer over a three-dimensional rough wall

PIV measurements in a turbulent boundary layer over a 3D roughened surface, consisting of pyramidal rows, are presented and compared to those for a smooth wall. The flow behaviour was tested for relatively high roughness and relatively low Reynolds number when the influence of the wall roughness may be expected to be noticeable. Mean flow expressed in velocity defect form, inner scaled streamwise Reynolds normal stress and Reynolds shear stress profiles show excellent agreement in the outer layer between the flow over the rough wall and the smooth surface. Wall-normal Reynolds normal stress profiles, instead, show some small discrepancy, but within the measurement uncertainty.