High resolution numerical and experimental studies of turbulence-induced sediment erosion and near-bed transport

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Analysis of turbulence-induced sediment erosion and near-bed transport is vital to many aspects of hydraulic engineering including the design of stable channels, protection of bridge piers, and the development and management of aquatic habitats, to mention a few. Most currently available relationships for predicting sediment erosion thresholds and bed-load transport rates are empirical and employ time- and space-averaged bulk quantities. The predictive power of these formulae is therefore low and errors may well exceed 100 %, which is a reflection of the lack of sound understanding of the physical mechanisms involved. The proposed study will address this knowledge gap using state-of-the-art physical experiments and numerical simulations of flows over spherical and naturally shaped roughness elements. Key research targets include identification and quantification of relationships between instantaneous flow fields (including the region below roughness tops) and resulting forces on sediment particles, assessment of individual bed-load particle trajectories and the interaction of turbulent flow and a multitude of mobile sediment particles. Among others, the effect of Reynolds number, flow submergence, sediment shape, and sediment packing on turbulence structure and near-bed transport will be addressed. The study will be based, for the first time, on the systematic use of highly-resolved numerical simulations with fully resolved mobile roughness elements coupled with advanced three-dimensional experimental measurements above and below mobile sediment beds. The project will bring together three research groups from two countries which complement each other with unique capabilities in addressing a common research goal.