Yang Yantao, Verzicco Roberto, Lohse Detlef
Physics of Fluids Group, MESA+ Institute and J. M. Burgers Centre for Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands;
Physics of Fluids Group, MESA+ Institute and J. M. Burgers Centre for Fluid Dynamics, University of Twente, 7500 AE Enschede, The Netherlands; Dipartimento di Ingegneria Industriale, University of Rome Tor Vergata, Rome 00133, Italy;
Proc Natl Acad Sci U S A. 2016 Jan 5;113(1):69-73. doi: 10.1073/pnas.1518040113. Epub 2015 Dec 22.
Double-diffusive convection (DDC), which is the buoyancy-driven flow with fluid density depending on two scalar components, is ubiquitous in many natural and engineering environments. Of great interests are scalars' transfer rate and flow structures. Here we systematically investigate DDC flow between two horizontal plates, driven by an unstable salinity gradient and stabilized by a temperature gradient. Counterintuitively, when increasing the stabilizing temperature gradient, the salinity flux first increases, even though the velocity monotonically decreases, before it finally breaks down to the purely diffusive value. The enhanced salinity transport is traced back to a transition in the overall flow pattern, namely from large-scale convection rolls to well-organized vertically oriented salt fingers. We also show and explain that the unifying theory of thermal convection originally developed by Grossmann and Lohse for Rayleigh-Bénard convection can be directly applied to DDC flow for a wide range of control parameters (Lewis number and density ratio), including those which cover the common values relevant for ocean flows.
双扩散对流（DDC）是一种由浮力驱动的流动，其中流体密度取决于两个标量分量，在许多自然和工程环境中普遍存在。标量的传输速率和流动结构备受关注。在此，我们系统地研究了由不稳定的盐度梯度驱动并由温度梯度稳定的两块水平板之间的DDC流动。与直觉相反，当增加稳定温度梯度时，盐度通量首先增加，尽管速度单调下降，最终才降至纯扩散值。盐度传输的增强可追溯到整体流动模式的转变，即从大规模对流涡旋转变为组织良好的垂直定向盐指。我们还展示并解释了最初由格罗斯曼和洛泽为瑞利 - 贝纳德对流开发的热对流统一理论可以直接应用于DDC流动，适用于广泛的控制参数（刘易斯数和密度比），包括那些涵盖与海洋流动相关的常见值的参数。
