Author(s): Hongwei Fang, Yan Liu, Thorsten Stoesser, Chenwei Zhao
Linked Author(s): Yan Liu
Keywords: : Large eddy simulation, dune propagation, sediment transport, three dimensional dunes, dune evolution
Abstract: Large eddy simulations are performed for open channel flows with sediment dune evolutions. The turbulent flow is simulated with Hydro3D, which has been performed successfully on flow over several complicated geometries. Sediment transport module, consist of bedload transport and bed morphology evolution module are imbedded into the Hydro3D by the current author. The coupling of sediment particles and turbulent flow is achieved by applying the direct-force immerse boundary method on sediment particles. The code is firstly validated on a flow with two dimensional sediment dune evolutions. Simulated dune height and dune length evolution processes are compared with the processes of flume experiments. A well agreement is gained between the simulation and the experiment. Then, two kinds of three dimensional sediment dune initiation processes are simulated, i. e. dune propagation processes from defects and dune instantaneous initiation occurred over the entire bed. For the dune propagation processes, three major feathers are observed during the simulation: new dune crests develop with decreasing H and L with distance downstream, bed form field widens forming a triangular shape, and the dune crests take on a uniform H and L in cross section. While for the dune instantaneous initiation processes, the observed sediment dune crests demonstrate three shapes, i. e. lobe, straight and saddle, which is similar to those found in natural rivers and in coastal areas. Further investigation of the non-dimensional span (NDS) shows that the NDS decreases with time increment, which agrees with those found in flume experiments. In terms of the turbulent events, sweeps and ejections occurs more frequently on dune stoss side than the other two events (inward and outward interactions)
Year: 2017