Large Eddy Simulation of Sediment Transport and Hydrodynamics at River Bifurcations: Using a highly scalable spectral element based CFD solver

Marcelo Garcia, University of Illinois at Urbana-Champaign

Usage Details

A fundamental morphological element present in most river-systems is a bifurcation. A bifurcation can form naturally or can also be engineered for various purposes. A diversion is a special kind of bifurcation; in which one of the post-bifurcation channels continues along the direction of the original un-bifurcated channel. Previous studies based on laboratory experiments have shown that at diversions, the near-bed sediments tend to enter the lateral channel, even in cases where the opposite trend is exhibited by the water discharge; this non-linear phenomenon is commonly known as the Bulle Effect. The current study attempts to fill the gap in fundamental understanding of the Bulle Effect and related phenomena, such as secondary flows and vorticity-driven sediment transport. Contrary to previous numerical studies in this area, the simulations in the proposed work will resolve all the relevant turbulence eddies of the flow; this will not only provide an accurate description of the dynamics of the flow, additionally it will also help to model the sediment transport phenomena accurately when coupled with a Lagrangian particle model for the sediment. The computational fluid dynamic simulations would be done using the open-source highly scalable spectral element Navier-Stokes solver Nek5000. The maximum Reynolds number of the planned simulations are of the order of 10⁴-10⁵, which compares favorably with laboratory experiments. The current study pushes the limit of the scale at which eddy-resolving numerical simulations have been used to study complex multi-phase river mechanics problems, warranting the use of a computational resource that can provide sustained computing power at an unprecedented scale, thus the need to use Blue Waters.