Long-running gravity currents are flows that are submerged beneath a deep layer of quiescent fluid and they travel over long distances along inclined or horizontal surfaces. They are driven by the density difference between the current and the clear ambient fluid above. In this work we present results on highly resolved direct numerical simulations of turbid underflows that involve nearly 1 billion degrees of freedom. We assess the effect of bed slope on the flow statistics. We explore the turbulence dynamics of the interface in the classical sub- and supercritical regimes. We investigate the structure of interfacial turbulence and its relation to the turbulence statistic. A transcritical regime is identified where intermittent cascading interfacial instabilities appear. We investigate how departure from the self-sustaining equilibrium state may be the mechanism responsible for this cyclic evolution of the transcritical regime.

长期运行的重力流是浸没在较深的静态流体层之下的流，它们沿着倾斜或水平的表面行进很长的距离。它们是由电流与上方的透明环境流体之间的密度差驱动的。在这项工作中，我们给出了涉及近10亿自由度的浑浊底流的高度解析直接数值模拟的结果。我们评估床坡度对流量统计的影响。我们探索了经典亚临界和超临界状态下界面的湍流动力学。我们研究了界面湍流的结构及其与湍流统计的关系。在出现间歇性级联界面不稳定性的地方确定了跨临界状态。