Modeling granular sediment transport over water worked gravels within a CFD framework

摘要

A numerical description of the hydraulics and sediment transport processes operating in a fluvial environment is far from complete due to the complex interactions between form, flow and sediment transport. Near bed turbulence determines the dynamics of sediment transport, however an analytical description of turbulent flow and sediment transport is subject to significant errors due to the poor parameterization of physical processes and that mean boundary shear stress is frequently determined from velocity profiles. This paper reports a numerical model that calculates the transport paths of individual granular particles over a natural water worked gravel surface. Surface topography is measured using digital photogrammetry and incorporated into a computational fluid dynamics (CFD) scheme by the application of a porosity algorithm. The predicted hydraulics determines the forces acting on each particle enabling the particle trajectory to be solved by Langrangian transport equations. The methodology demonstrates the importance of including complex topography in the numerical scheme as topographically induced hydraulic acceleration and deceleration affect both the transport mechanism and subsequent trajectory of the particle.