Turbulence in natural bed flows

Characterization of turbulence in natural bed flows is very complex and highly important owing to its numerous application in the field of sediment transport. In the present work a turbulent open-channel flow experiment, with a natural pebble bed at Re = 4.65 × 104 and Fr = 0.186, has been numerically simulated by means of the Large Eddy Simulation (LES) approach, in which the Wall-Adapting Local Eddy viscosity (WALE) subgrid scale (SGS) closure model is used. The simulations have been compared with a companion experiment, where the channel bottom is constituted by four natural-pebble layers. For the simulations, the pebble-bed surface has been captured with a high-resolution three-dimensional (3D) laser scanner and used to morphologically characterize the bottom of the numerical channel. Results are presented in terms of turbulence statistics and turbulent laws, showing a good agreement with those obtained in the companion experiment. A procedure for vortex-visualization is presented, based on the relationship between the vorticity and the Turbulent Kinetic Energy (TKE) dissipation rate.