MOMENTUM BASED MODEL FOR SEDIMENT TRANSPORT

Abstract eng:
Many current models of sediment transport use single-phase flow equations to determine liquid flow velocity profiles and then use these to compute suspended load and bed load transport. A two-phase or two-fluid approach is more desirable because it allows mechanistic modeling of interfacial effects as well as turbulence effects within the near-bed layer. This also seems to be a more natural approach than some existing two-fluid models, which often couple a conservation of momentum equation for the liquid (continuous) phase and includes a diffusive flux of dispersed material in the conservation of mass equation for the dispersed phase. The basic equations for two-phase flow are presented and applied to the simplified case of steady-state two-dimensional fully-developed flow in a rectangular channel over a flat bottom. The equations for balance of mass and momentum are discussed for low sediment concentration, and a k − ε turbulence model is considered. Parameters which affect the sediment volume fraction are determined through nondimensionalization of the model equations. The k − ε system is found to be singularly perturbed, with a boundary layer near the bottom. Singular perturbation analysis of the k − ε system is performed, with “law of the wall” boundary conditions coming from the near-bottom analysis. Subsequent numerical solutions for the sediment volume fraction show that this treatment of the k − ε equations produces reasonable results when compared with experimental data.

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