Flume LES of a glued spheres layer – Detailed analysis of initial motions of a single grain.

Highly resolved 3D Navier-Stokes simulations using a Large Eddy turbulence approach are becoming very popular these days due to fast and yet affordable processor architectures. The following paper deals with 3D Large Eddy Simulation (LES) of a 30 cm wide flume having a bottom with glued spheres of identical diameter (1 cm). In the centre of the test reach one single and mobile sphere, representing a sediment grain, was exposed to the flow and additionally could be moved into the flow by a stamp. Different flow fields were computed as initial conditions, from which the grain was protruded into the flow. This setup corresponds to a laboratory test setup used and described by Fenton and Abbot (1977). Like in the experiment the single grain is also in the numerical test fully coupled with the fluid and therefore a complete fluid-grain-interaction (two way coupling) is enhanced. For the computations a highly resolved mesh with 1x1x1 millimeter cells was used. The paper focuses on the basics of modeling and interpreting LES as well as on the analysis of the computed flow. Furthermore the initial motion of the numerical grain is investigated in detail by observing the fluid flow forces. First results for initial motions and the application of a probabilistic approach for beginning sediment transport are discussed.