Spatially Averaged Turbulent Flow over Square Ribs

Abstract

A series of experiments was undertaken to assess fully rough turbulent subcritical flow over two-dimensional transverse repeated-rib roughness of varying spacing λ∕h=1–16 (roughness spacing/height ratio), with h∕H=0.09 (roughness height/flow depth). Each of the 11 experiments involved centerline measurements of three-dimensional velocity vectors, water surface profiles, and bed pressures and forces. The structure of flow over rib roughness consists of a pair of principal vortices of opposite sign set up by the ribs. These vortices are superimposed on an overall double- (time and space)-averaged velocity profile that is (quasi-) logarithmic above roughness tops, and that below roughness tops changes with increasing rib spacing from exponential (λ∕h<10) to linear (λ∕h≥10) to logarithmic (λ∕h≫10) . The measured double-averaged velocity profiles are parameterized herein, and double-averaged Reynolds and form-induced stress profiles and trends are also identified. Maximum drag due to wall roughness is found to...