Numerical modelling of scour in steady flows
LI Ming - Lecturer - University of Liverpool - Rapporteur
FUHRMAN David - Associate Professor - Technical University of Denmark - Rapporteur
ROCA Marta - Principal Engineer - HR Wallingford - Examinatrice
RIVIÈRE Nicolas - Professeur - INSA Lyon, LMFA - Examinateur
PERKINS Richard - Professeur - Ecole Centrale de Lyon, LMFA - Directeur de thèse
This thesis describes the development of a numerical model for local scour caused by bedmounted obstacles, combining the hydrodynamic and morphological processes.
The basis of the numerical model is the multiphase flow solver in the open-source CFD toolbox OpenFOAM® which is released by OpenCFD Ltd. The hydrodynamic module of the model solves the Reynolds Averaged Navier-Stokes (RANS) equations. There are two interfaces in the simulation domain : the free surface between water and air, which is tracked using the Volume of Fluid (VOF) method, and the interface between the water and the sediment, which is represented by a finite area mesh constructed from the bottom boundary of the finite volume mesh. A morphological module which has been developed as part of the project consists of three components : a sediment transport model which includes suspended load and bed load transport ; the Exner equation to compute the bed deformation, and a sandsliding mechanism to restrict the bed slope angle to be smaller than the angle of repose. The
morphological changes are incorporated into the hydrodynamic field through deformation of the computational mesh. The numerical model is then applied to study two-dimensional scour caused by a submerged jet and the three-dimensional scour around a cylinder in flow. The influences of the variation of the water depth on the flow field are identified and discussed. The development of the scour processes with time and the computed maximum scour depths agree quite well with the experimental measurements. The influences of the scour process on the flow field are also discussed.