Doctor of Philosophy (PhD)
Civil and Environmental Engineering
The motivation of this study is to extend applications of Large Eddy Simulation (LES) for typical open channel flows to elucidate the time dependent three dimensional flow and sediment transport features which are usually difficult to measure in experiments. Detailed investigations are performed on the unsteady features and, in particular, turbulent structures of the flow to demonstrate the great potential of eddy resolving methods. The instantaneous flow and sediment transport fields are investigated together with the existence of coherent structures. These structures together with ejection events (u' < 0, w' > 0), are responsible for the vertical and lateral transport of suspended sediment from the near bed region. Stronger velocity perturbation vectors are also observed around the coherent structures, demonstrating that these areas are highly dynamic zones of flow and sediment transport. As a result of the enhanced viscosity, sediment induced stratification, and particle pressure effects, a reduction on the peak turbulence levels is shown for both the wall normal and Reynolds shear stress components in the sediment concentrated recirculation and near-bed regions. These phenomena can potentially decrease the vertical mixing and turbulent suspension of sediment particles in the flow field. Three dimensional hydrodynamic simulations are also conducted for ~10 meter section of the Expanded Small Scale Physical Model (ESSPM) of the Lower Mississippi River to gain insights on the effects of model distortion on various hydrodynamic variables. Analysis and comparisons are carried out at two distortion scales (i.e., 15, the design distortion and 7.5) using turbulence resolving simulations. Overall, the difference in horizontal mean velocity profiles and velocity fluctuations from the two distortion levels is small, supporting the ability of a distorted models to replicate bulk 1-D sediment transport rates. The work presented in this dissertation demonstrates that LES is advantageous for solving the complex flow and sediment transport dynamics by resolving the large scale eddies of the turbulent motion and that, when coupled with a sediment transport model, will provide valuable insights into three dimensional turbulence-sediment interactions.
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Agegnehu, Getnet Baynesagne, "Applications of Large Eddy Simulation to Study Flow and Sediment Transport in Open Channel Flows" (2015). LSU Doctoral Dissertations. 2684.
Willson, Clinton S