论文标题
自我分层的浊流
Self-stratifying turbidity currents
论文作者
论文摘要
浑浊电流，悬浮颗粒密度过多的海底流，是沉积物，营养素和污染物的关键输送体，从大陆边缘到深海，并带来关键的海底地球扎华风险。由于它们的规模巨大和极端纵横比，现存的模型被限制在高度简化的深度平均理论上，并且无法捕获观察到的行为。我们提出了一个新型的深度平均模型，该模型捕获了内部能量平衡和速度，深度和湍流动能的垂直轮廓。随着电流的发展，垂直轮廓发生了变化：它自我分层。这使得一个关键的新见解是，通过平均流动，湍流和引力势能之间的双向级联反应构成浊度电流的传播。 该模型被概括为完全限制的“峡谷”流（不侧向溢出），并部分限制了“通道”流（侧向溢出到边界堤防）。构建了用于自分层浊流的“准平衡”解决方案。这些解决方案每周不稳定，并连接到一个缓慢发展的歧管，其中可能会发现环境电流。发现用于通道流的平衡解决方案也不稳定。堤防过度刺激消除稀释，低动量流体，使流动恢复活力，这可能会导致液体越来越浓缩的正反馈回路。我们通过在刚果峡谷通道系统中建模流量来测试新理论，这是首次模拟将100 km传播到现实世界系统远端的超临界浊度电流。结果表明，自分层增强了材料和动量通量，从而确定了这种流量的环境影响和风险。
Turbidity currents, seafloor flows driven by the excess density of suspended particles, are key conveyors of sediment, nutrient, and pollutant from the continental margins to deep ocean, and pose critical submarine geohazard risks. Due to their vast scale and extreme aspect ratio, extant models are constrained to highly simplified depth-averaged theory and fail to capture observed behaviour. We propose a novel depth-averaged model capturing the internal energy balance and the vertical profiles of velocity, depth, and turbulent kinetic energy. The vertical profiles change as the current evolves: it self stratifies. This enables the critical new insight that turbidity current propagation is enabled by bidirectional cascades between mean-flow kinetic, turbulent, and gravitational potential energies. The model is generalised for fully confined `canyon' flow (no lateral overspill), and partially confined `channel' flow (lateral overspill over bounding levees). `Quasi-equilibrium' solutions for self-stratifying turbidity currents are constructed. These solutions are weekly unstable and connected to a slowly evolving manifold, wherein environmental currents are likely found. Equilibrium solutions, found for channel flow, are not stable either. Levee overspill removes dilute, low momentum fluid, rejuvenating the flow, which can cause a positive feedback loop where the fluid becomes increasingly concentrated. We test the new theory by modelling flow in the Congo canyon-channel system, for the first time simulating a supercritical turbidity current that travels 100s km to the distal reaches of a real-world system. It is shown that self-stratification enhances material and momentum fluxes, determining the environmental impacts and risks from such flows.
