Three-dimensional Numerical Analysis of Flow Structure and Sediment Transport Process in Open Channels

Book excerpt: This research project focuses on the analysis and prediction of flow structures and sediment transport process in open channels by using three-dimensional numerical models. The numerical study was performed using the open source computational fluid dynamics (CFD) solver based on the finite volume method (FVM) – OpenFOAM. Turbulence is treated by means of the two main methodologies; i.e. Large Eddy Simulation (LES) and Reynolds-Averaged Navier–Stokes (RANS). The free surface is tracked using the Volume of Fluid method (VOF). In addition, a new multi-dimensional model for sediment transport based on the Eulerian two-phase mathematical formulation is applied. The results obtained from the different numerical configurations are verified and validated against experimental data sets published in important research journals. The main characteristics of the flow structures are studied by using three set-up cases in steady and unsteady-state (transient) hydraulic flow conditions. On the other hand, the new multi-dimensional model for sediment transport is applied to predict the local scour caused by submerged wall jet test-case. Non-uniform structured elements are used in the grid configuration of the computational domains. A mesh sensitivity analysis is performed in each test-case study in order to obtain independent grid results. This analysis provides a balance between accuracy and optimal computational time. The results demonstrate that the three-dimensional numerical configurations satisfactorily reproduce the temporal variation of the different variables under study with correct trends and high correlation with the experimental values. Regarding the analysis and prediction of the flow structures, the results show the importance of the turbulence approach in the numerical configuration. On the other hand, the results of the new multi-dimensional two-phase model allow to analyze the full dynamics for sediment transport (concentration profile). Although the numerical results are satisfactory, the application of three-dimensional numerical models in field-scale cases requires a high computational resource.