Dynamics of Coherent Structures and Sediment Transport in High-Reynolds Number Turbulent Flows

Abstract

Large-scale unsteady coherent structures emerging from flow instabilities constitute important mechanisms of initiation of motion and sediment transport in engineering and geophysical applications. Numerical simulations of these flows are particularly challenging, especially if the objective is to capture the dynamic features of the flow at high-Reynolds numbers in complex geometries. To investigate the large-scale vortical structures that arise as a result of pressure gradients imparted on the flow by local streamline curvature or embedded solid obstacles, we carry out detached eddy simulations (DES), which successfully resolve the complex dynamics of the turbulent horseshoe vortex system around surface-mounted obstacles, and Görtler vortices in concave sediment beds. These simulations show that the numerical methods reproduce with very good accuracy all the experimental observations of mean flow quantities and turbulence statistics. Motivated by the results obtained for these flows we develop Lagrangian and Eulerian sediment transport models, which are capable of reproducing the complex dynamics of particles observed in experiments, such as intermittent bed-load transport near the threshold of motion, and the development and evolution of bedforms in fine sand.