Author(s): Ronja Ehlers; Widar Weizhi Wang; Arun Kamath; Hans Bihs

Linked Author(s): Hans Bihs

Keywords: Local Scour; Level set method; Sediment transport; Abutment; Pile

Abstract: This paper presents the prediction of local erosion of cohesionless sediment around two simple structures under steady current with a three-dimensional numerical multiphase model. Local scour around abutments and piers is a significant concern in hydraulic engineering since it can lead to bridge failure. The two studied cases feature (1) a rectangular abutment which constricts the channel from the sidewall and (2) a cylindrical pier located in the channel center. The hydrodynamics are calculated by solving the incompressible Reynolds-Averaged Navier Stokes (RANS) equations in combination with the k-o> turbulence model on a staggered grid. The interfaces are captured by the Level Set Method (LSM). Fluid - structure interaction is possible through a ghost cell immersed boundary method. The morphodynamic module calculates the bed level change based on a mass balance equation. The bed load is based on an excess-shear stress formulation. The bed shear stress is obtained by its relation to turbulent kinetic energy. The algorithm considers a slope effect on the critical shear stress and sand sliding. The numerical results are validated against experiments from the literature. Flow related local morphodynamic processes have been studied intensively while it remains a challenge to numerically predict erosion around structures. The paper demonstrates a robust approach to model the local scour process under current around two different structures - a rectangular abutment and a cylindrical pier - with free surface capturing. The maximum erosion depth is predicted with a small difference of the final maximum scour depth of 0.017 m (abutment) and 0.004 m (pier). The extent of the scour around the structure correlates with the measurements while the downstream scouring process is slightly overpredicted in case of the abutment. The decoupling of the hydrodynamic and morphologic time scale and the cell size of 0.02 m enables a time efficient prediction. Focus for further development are applications with complex free surface flow to investigate the effect of different flow situations.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p1460-cd

Year: 2023