Spatially-averaged turbulent flow over square-rib roughness

摘要

In order to investigate the influence of changing bed morphology on flow structure (e.g. velocity and momentum-flux profiles), a series of 11 tests of fully-rough turbulent subcritical flow over two-dimensional transverse repeated square ribs was undertaken in which the ribs were varied (for a single flowrate) to give uniform rib spacing-to-height ratios of λ/h = 1-16. The double- (time- and space-) averaged velocity profile is found to be (quasi) logarithmic above roughness tops, changing below roughness tops with increasing rib spacing from exponential (λ/h < 10) to linear (λ/h ≥ 10) to logarithmic (λ/h 10). The experimentally-determined momentum balance, including effects of secondary currents, flow acceleration, and Reynolds and form-induced stresses, is found to agree well with theoretical expectations. It shown that the knowledge of the effects of form-induced stresses, secondary currents, and flow non-uniformity can be particularly important for describing and modeling flows over roughness elements.