Velocities and Turbulent Stresses of Free-Surface Skimming Flows over Triangular Cavities

Velocity distributions in supercritical open-channel flows over stepped cavities have traditionally been described using a power-law approach or theoretical solutions of plane mixing layers. These approaches were found to be valid either above the step edges or above/within step cavities, but no generalized model is available. In this study, a four-layered velocity model is proposed, which combines different physical concepts, including the mixing layer, log-layer, wake function, and free-stream layer. This multilayer model was applied to previous experimental stepped chute data, providing novel opportunities to comparatively assess the relative contribution of individual physical effects on the velocity profile. Model parameters provided insights into flow hydrodynamics, comprising mixing layer length scales and shear velocities. Equations for Reynolds shear stresses within the different layers were formulated using an eddy viscosity concept, while normal stresses and turbulent kinetic energy compared well to semitheoretical open-channel flow equations.