Large Eddy Flow Simulation for the prediction of bank erosion and transport processes in river bends (DCB.6787)

Research:
This project is aiming at the realization of a numerical tool for the prediction of flow and turbulence in river bends with application to bank erosion and transport processes. Since all rivers have the natural tendency to meander, curved rivers are ubiquitous in nature and most transport processes are dominated by the effects of curvature. In order to predict the evolution of a curved flow reach and its ever-changing bathymetry a clear insight into the details of the flow, the turbulence and their transporting capacity is of key importance. Preceding experimental and numerical research performed at TU Delft and EPF Lausanne has shown that secondary flow and turbulence play a predominant role in the transport and erosion processes and are highly influenced by the shallowness and curvature of the flow.
Our ongoing research programme, of which the proposed project is part and parcel, aims at gaining insight into the physics of curved flow and improving our engineering tools, by means of a combined experimental-numerical research methodology (see Panel 3).
Since experimental data can only be gathered with limited detail and for a restricted range of geometries, the present project proposes to develop a 3D-simulation tool that comprises all relevant dynamics of the flow in real-life river configurations. After validation with our experimental data, this model can unravel and parameterise the details of the 3D turbulent motion for a wide range of flow and geometric parameters. Emphasis will be put on wall shear stresses, associated bank erosion and bank stability as well as on longitudinal transport and dispersion processes, with the aim of improving their modelling in engineering tools.
In this project the expertise of research groups from EPF Lausanne, TU Delft and WL|Delft Hydraulics is combined in order to create synergy and use experimental data and modelling experience efficiently.

Utilization:
At present, the rational design of river re-naturalization projects, the inherent bank protection schemes, and the water quality management in combination with intense navigation are headaches to many river managers. This is for an important part due to the insufficient insight into the mechanisms of the underlying hydrodynamic and morphodynamic processes and the lack of reliable simulation tools. In contrast with many laboratory situations, real rivers follow a winding course in which the curvature of the flow is an essential feature with great consequences for the hydrodynamic, morphodynamic and transport processes. Relevant issues in this respect concern: river renaturalization projects, smart river training by means of bottom vanes, sediment distribution at river bifurcations, estuarine morphodynamics.
Every change in the river bed and its flood plains should be analysed with respect to its impact on discharge capacity, navigable depth and ecology. The costs for dredging or hindrance for navigation are simply too high to refrain from in depth analyses, let alone the risk associated with flooding due to bank failure.

Modelling tools that properly represent the relevant physics of curved flows in real-life river configurations are not available at this moment or have a limited predictive capacity. The proposed research project, as it is embedded in our broader research programme (see Panel 3), will provide an important contribution in fulfilling this need. This project will bridge the gap between laboratory scale and full-scale applications with the Large Eddy Simulation tool as a necessary means for validation and parameterisation. The close collaboration between experimentalists, numericists and users of models guarantees an efficient transfer of knowledge towards numerical prediction tools. Moreover the utilisation benefits from involvement of researchers with close ties to practice.

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