Velocity scales in steady-nonuniform turbulent flows with low relative submergence

Abstract

The most employed velocity scale in open-channel flows is the shear velocity. Although it is effortlessly identified in uniform flow condition, its value becomes elusive to find in nonuniform flow condition. Furthermore, in low relative submergence flows, the absence of the universal log-law velocity distribution eliminates the methods which exploit the logarithmic velocity profiles in order to compute the shear velocity. The aim of this work is to find a tool to compute a better scaling velocity in uniform and nonuniform flows with low relative submergence. In particular, laboratory tests were performed and the characteristics velocities were computed through the momentum balance, the kinetic energy balance and the 4/5 law of turbulence. These velocity scales were compared for the first time in flows with low relative submergence, showing that the best velocity scale can be obtained through the application of the well-known Kolmogorov 4/5 law. This study is focused on possible applications to the natural environment, where indeed the bed type is highly inhomogeneous and irregular. The results obtained with the acoustic Doppler velocimeter technique suggest that accurate measurements and analysis are fundamental not only in laboratory settings but also in natural environment flows.