Author(s): Tino Kostic; Yuanjie Ren; Stephan Theobald

Linked Author(s): Tino Kostic, Stephan Theobald

Keywords: •Channel bifurcations; •3D CFD sediment simulation; •Numerical replication of physical models

Abstract: Knowledge of sediment transport behavior in rivers and around hydraulic structures can greatly improve their design, operation and cost efficiency while benefitting the local environmental impact regarding natural river morphodynamics. Sediment can be transported in form of suspension and bedload, whereas the later is of particular interest for stability and functionality of hydraulic structures. Although methods of 3D computational fluid dynamics (CFD) are used successfully over decades for solving fluid flow problems in hydraulic engineering, 3D-CFD simulations of sediment transport, particularly bedload, are still in its infancy. Complex flow characteristics around hydraulic structures in addition to empirically derived formulas for bedload transport make it especially challenging to consistently solve problems regarding bedload transport and to determine rules and recommendations for future sediment CFD simulations. In a previous research, a model of a channel bifurcation investigated by Dr.-Ing. Herman Bulle in 1926 was numerically recreated. In that research, a bifurcated branch was split from the main straight channel at approximately half of its length, while sediments were added in the running model. The results showed that, for an equal discharge in both of the branching channels, the majority of added sediments, which were transported as bedload, landed mostly in the bifurcated channel. The experiment was repeated for models with various splitting angles. This paper presents results of numerical investigations of the original Bulle bifurcation in brief, supplemented with further findings about bedload transport in the channel bifurcation for various flow conditions. Additionally to the Bulle bifurcation, a series of physical model investigations on another channel bifurcation was conducted in the hydraulic testing facilities of University of Kassel. Results from numerical investigations of this bifurcation model are shown in the paper as well. All numerical simulations were conducted with the commercial CFD software Flow-3D. The bifurcation channels from Bulle and from University of Kassel differ in size, model material, used sediment and applied boundary conditions. Therefore, different numerical bedload parameters were used for their recreation. CFD simulations from both bifurcation models give insights in bedload behavior in channel branching as well as some general recommendations for numerical simulations of sediment transport.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022732

Year: 2022