This project is jointly funded by NSF and the Army Research Office (ARO) and seeks to develop and validate the first 3D, unsteady, numerical model capable of accurately reproducing bridge foundation scour. The basic premise of this work is that fluctuating hydrodynamic forces due to the foundation-induced unsteady coherent vortices drive sediment transport and scour and need to be modeled correctly. Available methods are incapable of capturing the inherently unsteady physics of the problem as they either rely on qualitative descriptions, empirical correlations or employ statistically stationary computational models. To overcome these shortcomings, a research partnership is established among St. Anthony Falls Laboratory (SAFL), Virginia Tech (VT), and the US Army Corps of Engineers (USACE) WES facility. The objective is to integrate the latest developments in 3D coherent-structure resolving numerical modeling of turbulent junction flows with state-of-the-art laboratory capabilities and instrumentation, which permit simultaneous measurements of instantaneous flow quantities and pressures with the corresponding spatial and temporal development of the scour hole. A novel Eulerian model of bedload transport will be developed, which employs Lagrangian ideas to account for the effect of near-bed fluctuating hydrodynamic forces into Exner's equation. Preliminary work has demonstrated the ability of this model to reproduce the highly dynamic evolution of the scour hole including the formation of complex bedforms. The following tasks will be accomplished in this project: a) experimental validation of the hydrodynamic model, b) experiments for monitoring the flow structures simultaneously with the scour hole evolution, instantaneous pressures on the pier and on sediment particles over a wide range of pier diameters, sediment sizes, and flow characteristics, with some of them representative of near-prototype conditions, and c) further development and validation of the new unsteady model of bedload transport. The laboratory experiments will be carried out at thirteen pier-diameter based Reynolds numbers (ranging from 4x104 to 6.7x105), while the numerical model will explore these as well as a wider range of Reynolds numbers.
This project will advance, in a collaborative effort, the development of a computational model capable of scour prediction in practical flow conditions, as well as advance our knowledge and understanding of the phenomenon, including upscaling effects. The outcomes of the project will benefit society by providing a powerful computational tool that can be used to study and develop mitigation strategies for the bridge scour problem, which has resulted in more bridge failures than all other causes in recent history and has the potential to seriously impair the nation's transportation infrastructure. The numerical model will also enhance significantly our research infrastructure by providing a tool that can be used to tackle a wide range of stream restoration problems. In this regard the model can be applied to develop improved criteria for stream restoration studies that account for the flow structures around boulders and other obstructions affecting stream habitat quality. The potential impact of this work to stream restoration and outreach activities will be greatly facilitated through cross-disciplinary interactions with the NSF National Center for Earth Surface Dynamics housed at SAFL.
Research in this project was driven by the major societal need to design transportation infrastructure, such as bridge foundations in rivers and streams, that is resilient to streambed erosion and ultimate collapse due to scour-related failure during flooding events. The specific objective of this work is to develop an accurate and efficient high-performance computing computational fluid dynamics model capable of simulating the interaction of turbulent flow of water in waterways with sediment beds and hydraulic structures in order to accuratelly predict the scour potential of hydraulic structures during flooding events. The numerical model accounts, for the first time, for the interaction of the complex, three-dimensional, unsteady turbulent flow around bridge piers and other hydraulic structures with the evolving mobile sediment bed in natural waterway environments. Detailed laboratory experiments conducted at the St. Anthony Falls Laboratory (SAFL) of the University of Minnesota and the Baker Environmental Hydraulics Laboratory at Virginia Tech provided data of unprecented resolutionwhich were used to validate the computational model and demonstrate its predictive capabilities. The project has contributed to the develpment of the next generation of flow and sediment transport simulation tools using high-performance computational platforms. The computational framework, which is referred to as the Virtual StreamLab (VSL3D), is capable of carrying out high-fidelity numerical simulations of coupled hydro-morphodynamic processes in real-life waterways with arbitrarily complex hydarulic structures. As such, VSL3D has provided the hydraulic engineering community with unprecedented capabilities for simulation-based research and the opportunity to solve scour-related problems and develop transportation infrastructure that is resilient tof lflooding by relying on sound understanding of the underlying physical phenomena. In addition to bridge foundation flows, the VSL3D code has already made a major impact in the area of stream and river restoration. The software has been used to develop the first ever design guidelines of in stream structures, which are based on predictive understanding of how structures interact with turbulent flow and sediments in natural waterways. A major advance in that regard is the ability of VSL3D to simulate river morphodynamcis including the dynamics of bedforms across a range of scales, from small-scale ripples to mega-dunes in large rivers. The code is also making an impact in the field of stream ecology as it has been extended to predict nutrient uptake in natural waterways. In addition VSL3D has also been extended to simulate the coupled interactions of hydrokinetic turbines with waterways and sediment beds. Finally, this code has been at the center of a brand new NSF PFI-BIC project seeking to use VSL3D to design the hydrokinetic turbines and optimize the layout of the multi-turbine array currently under development at the Roosvelt Island Tidal Energy project in New York City via simulation-based research
