Ongoing development of a three-dimensional sedimenttransport model for local scour study

Erosion due to scouring processes around hydraulic structures is a major topic in hydraulic engineering. Despite more than a century
of active research, its accurate prediction remains poor and its numerical modelling is still a major challenge for civil engineers.
Different studies have particularly identified scouring phenomenon as a major cause for bridge failures making its forecasting of
outermost importance to assess bridge safety and resiliency to extreme events. Numerical prediction of scour around an obstacle
requires the accurate simulation of the complex turbulent fluid flow in the vicinity of the structure as well as its interactions with
the surrounding sediment and the bed morphology. This involves a wide variety of processes such as bed-load transport, turbulent
suspension and gravity-driven avalanches. The classical morphodynamics models used in the industry, although adapted to study
sediment transport at large scales, often fail to accurately simulate the scour process as well as the flow around hydraulic structures.
A detailed comparison of the flow hydrodynamics around a wall-mounted cylinder using TELEMAC-3D and OpenFOAM will be
presented. Furthermore, scour processes concern a wide range of structures with complex geometries that geophysical numerical
models are not able to consider e.g. vertical non-emerging structures or structures with pressurized flows. Other models better
reproduce the local physical processes such as SedFoam, based on a two fluid approach where the sediment is modeled as a continuum.
Unfortunately, the computational cost of such a model remain to high for engineering purposes. Those considerations emphasize the
need for an intermediate-scale model, able to solve the different turbulent flow structures associated with scouring at an affordable cost.
The development of such a model is the main objective of the present study and as first step, idealized benchmarks on sedimentation,
turbulent suspension and dune migration will be presented. In the future, ongoing work using SedFoam will be used to develop new
closures, that will be tested in the present model, which will be made open source.
This thesis work is carried out within the framework of the Oxalia Hydraulics Chair of the Grenoble INP Foundation.