Direct numerical simulation of shallow flows over a rough bottom boundary: On the interaction between the deformable free-surface and the roughness-generated turbulence

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Free-surface shallow flows are ubiquitous in nature. They are found in lowland alluvial rivers, estuaries, coastal areas and in man-made canals. The air-water interface in such flows is commonly observed to undergo a continuous spatio-temporal evolution featuring waves at a wide range of scales. Fundamental understanding of the mechanisms behind the free-surface dynamics is crucial from an environmental and engineering point of view as it greatly influences a number of relevant processes such as sediment and solute transport, interfacial mass and heat transfer and pollution dispersion. The rich dynamics of the free-surface is a consequence of a complex interplay between stabilizing and destabilizing factors such as gravity, the chaotic turbulent motion of the flow beneath and the evolving sediment bed. The proposed project aims to numerically investigate the physical mechanisms behind the often observed free-surface phenomena in turbulent shallow flows. To this end, a dedicated tool which utilizes state-of-the-art computational resources to simulate large-scale free-surface flows will be developed. Subsequently, the tool will be deployed to generate high-fidelity numerical data which resolves all the relevant scales of the problem. Rigorous analysis of the generated data will then follow to address the aforementioned coupled-interaction among the free-surface, the turbulent flow and the bottom rough bed. The results obtained in this project will fill existing knowledge gaps concerning the free-surface dynamics in environmentally-relevant shallow flows. It is anticipated that the results will serve as an important input in improving predictive models of the intrinsic processes in such flow configuration.