Rough-wall boundary layers in adverse pressure gradients

Smooth- and rough-wall boundary layers and fully developed pipe and duct flow investigations are reviewed. It is shown that the effect of roughness on the flow away from the wall can be accounted for by using an equivalent viscosity ν e . This viscosity is thought to depend only on the variables at the wall, such as shear stress τ 0 , fluid density ρ, viscosity μ and the roughness size and geometry and that the relationship between these variables is the same for both boundary layers and duct flow. However, experiments to date have been confined to the ‘rough régime’ and to boundary layers with a zero pressure gradient. Experiments were performed and the results show that the above finding can be extended to boundary layers with adverse pressure gradients in the rough régime. A general method for measuring the local boundary-layer characteristics, with roughness and pressure gradients present, is developed.