Evaluating of two phase models for numerical Simulation of sediment transport in a 180 degree Bend with lateral intake

A large number of flows encountered in nature and technology are a mixture of phases. Advances in computational fluid mechanics have provided the basis for further insight into the dynamics of multiphase flows. Currently there are two approaches for the numerical calculation of multiphase flows: the Euler-Euler approach and the Euler-Lagrange approach
In the Euler-Euler approach, the different phases are treated mathematically as interpenetrating continua. In FLUENT, three different Euler-Euler multiphase models are available: the volume of fluid (VOF) model, the mixture model, and the Eulerian model. For sedimentation, we must use the Eulerian model. The Eulerian multiphase model in FLUENT allows for the modeling of multiple separate, yet interacting phases. The phases can be liquids, gases, or solids in nearly any combination. The Lagrangian discrete phase model (DPM) in FLUENT follows the Euler-Lagrange approach. The fluid phase is treated as a continuum by solving the time-averaged Navier-Stokes equations, while the dispersed phase is solved by tracking a large number of particles through the calculated flow field.
Sediment transport by fluid flow is one of the most important two phase flow in the nature. Due to existence of secondary current in channel bends, the mechanism of flow and sediment transport in these channels is much complex and locationg lateral intake at outer bank of the bens decreases this compelexity.
In this paper, mechanisms of sediments transport into the intake in a 180 degree bend channel with lateral intake have been simulated whit the Eulerian and Discrete phases models in fluent software. The intake is located at the outer bank of an 180o bend at position 115° with 45° diversion angle. The effect of diversion discharge rate and diversion angle on mechanism of sediment entry to the intake was considered.
The turbulence model is k-ε model. Model҆s in different time has performed and the result compared with laboratory result.The results show in Qr=40%, the mechanism of sediment entry was consist of continues entrance from downstream edge of intake and periodic entrance from upstream of the intake, however in Qr=25%, the mechanism of sediment entry was only consist of continues entrance from downstream edge of intake. The two models (Eulerian and Discrete phases) have shown good results. The rout mean square errors for outer boundary of the path of the particle at the channel ҆s bed for two discharges (25% and 40%) have measured.
The number of particle in discrete phases is limited; therefore this model cannot be display the depth of sediment. The Eulerian model displays the bed topography very well. Measuring mean square errors show that the model operation for topography simulation is very well. This model shows the location of intermittent dune and location of sediment accumulation very well. The discrete phase model can be shown the particle trapped place better than the Eulerian model.
Due to increase in intake discharge, dimension of sediment accumulation is decrease. the mechanism of sediment entry to lateral intake is affected by diversion angle of intake. the minimum sediment is entered to lateral intake at diversion angle equal to 50 degree.