Fluid-particle interaction in turbulent open channel flow with fully-resolved mobile beds

- Phase-resolving, high-resolution data for collective particle motion of a large number of particles in a large computational domain is provided.
- Systematic comparison of the impact of the parameters mass loading and mobility on bed-load transport is performed.
- Suitable statistical tools to describe the governing properties of the fluid field and the sediment are introduced.
- A detailed statistical evaluation of fluid and particle properties for three different simulations is given.
- Applicability of the immersed boundary method together with a proper collision model on a large scale is demonstrated.

The paper presents Direct Numerical Simulations of an open channel flow laden with spherical particles at a bulk Reynolds number of 2941. The transport of thousands of mobile particles is simulated propagating over a rough bed which consists of immobile particles of the same size in hexagonal ordering. An Immersed Boundary Method is used for the numerical representation of the particles. With 22 points per diameter even the viscous scales of the flow are resolved at this Reynolds number. The reference run contains just as many fixed as mobile particles with a relative density slightly above the nominal threshold of incipient motion. Further runs were conducted with decreased mass loading and decreased Shields number together with a simulation containing only immobile particles. The variation of the parameters defining the mobile sediment yields a strong modification of particle-fluid as well as particle-particle interactions yielding different structures in space and time. This is assessed by means of appropriate statistical quantities addressing the continuous and the disperse phase. The results are in qualitative agreement with experimental observations at higher Reynolds number.