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

自由表面浅水流在自然界中无处不在。它们存在于低地冲积河流、河口、沿海地区和人工运河中。在这种流动中，通常观察到空气-水界面经历了一个连续的时空演变，在大尺度上表现为波浪。从环境和工程的角度来看，对自由表面动力学背后机制的基本理解是至关重要的，因为它极大地影响了许多相关过程，如沉积物和溶质运输，界面质量和传热以及污染扩散。自由表面丰富的动力学是稳定和不稳定因素之间复杂相互作用的结果，这些因素包括重力、下面水流的混乱湍流运动和不断演变的沉积层。提出的项目旨在数值研究在湍流浅层流动中经常观察到的自由表面现象背后的物理机制。为此，将开发一个专门的工具，利用最先进的计算资源来模拟大规模的自由表面流动。随后，该工具将用于生成高保真的数值数据，从而解决问题的所有相关规模。然后将对生成的数据进行严格的分析，以解决上述自由表面、湍流和底部粗糙层之间的耦合相互作用。在这个项目中获得的结果将填补有关环境相关浅层流动的自由表面动力学的现有知识空白。预计这些结果将作为重要的输入，用于改进这种流动结构的内在过程的预测模型。

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.