Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 32611, USA.
ExxonMobil Upstream Research Company, Houston, TX, 77389, USA.
Nat Commun. 2021 Mar 12;12(1):1649. doi: 10.1038/s41467-021-21966-y.
Turbidity currents are sediment-laden flows that travel over a sloping bed under a stagnant ambient fluid, driven by the density difference between the current and the ambient. Turbidity currents transport large amounts of carbon, nutrients and fresh water through oceans and play an important role in global geochemical cycling and seafloor ecosystems. Supercritical currents are observed in steeper slopes. Subcritical currents are observed in milder slopes, where the near-bed and interface layers are prevented from interacting across the velocity maximum. Past works show the existence of such a barrier to vertical momentum transfer is essential for the body of the subcritical current to extend over hundreds of kilometers in length without much increase in height. Here we observe the body of subcritical currents to have a three layer structure, where the turbulent near-bed layer and the non-turbulent interface layer are separated by an intermediate layer of negative turbulence production. We explain the mechanism by which this layer prevents the near-bed turbulent structures from penetrating into the interface layer by transferring energy back from turbulence to the mean flow.
浊流是一种在静止环境流体下，沿倾斜床面流动的含沙流，由流体内外的密度差驱动。浊流通过海洋输送大量的碳、营养物质和淡水，在全球地球化学循环和海底生态系统中发挥着重要作用。在更陡峭的斜坡上可以观察到超临界流。在较平缓的斜坡上可以观察到亚临界流，在那里近床层和界面层被阻止在速度最大值处相互作用。过去的工作表明，这种对垂直动量传递的阻碍对于亚临界流的主体在不增加太多高度的情况下延伸数百公里是至关重要的。在这里，我们观察到亚临界流的主体具有三层结构，其中，湍流近床层和非湍流界面层由负湍流产生的中间层隔开。我们解释了通过将能量从湍流转移回平均流来防止近床层湍流结构穿透界面层的机制。
