Numerical Investigation Of Natural Rough-Bed Flow

The turbulent flow in natural rough-bed watercourses is a rather complex phenomenon, still poorely investigated. The majority of the existing works on this subject are of experimental nature, while the numerical ones are mostly related to arti ficially and regularly roughened beds. In the present work a numerical investigation is carried out, in which the fully turbulent flow in an open channel is simulated, where the channel bottom is constituted by natural-pebble layers. In the numerical simulations, the LES approach is used (Large Eddy Simulation), in conjunction with the WALE (Wall-Adapting Local Eddy viscosity) SGS closure model (Sub-Grid Scale) at Reynolds number 46500 and Froude number 0.186. For the simulations, the pebble-bed surface has been captured from the bottom of a laboratory flume with a high-resolution 3D laser scanner, and used to morphologically characterize the bottom of the numerical channel. The Finite-Volume discretized governing equations are solved numerically by means of the InterFOAM solver, embedded in the OpenFOAM C++ libraries. In order to take into account the free-surface dynamics, the VoF (Volume of Fluid) method is used. A CPU-based computational system has been used for the computations. The system included one worker node equipped with two 8-core Intel E5-2640 CPUs (a total of 16 cores/16 threads at 2.0 GHz), 128 GB RAM at 1899 MHz, and 4 TB disk space. The code has been parallelized through the public domain OpemMPI implementation of the standard Message Passing Interface (MPI). The results of the simulations are compared with those obtained in a companion experiment mainly in terms of turbulence statistics of different orders, obtaining a rather good agreement. Moreover, the vorticity field has been visualized using the relation between vorticity and Turbulent Kinetic Energy (TKE) dissipation.