Multiple diffusion of heat and scalar in rotating stratified turbulence

采用快速畸变理论、直接数值模拟和湍流涡波模型研究了分层旋转湍流中热量和标量的多重扩散。在以往的研究中，双扩散问题都是作为一个流体运动的稳定性问题来研究的，没有研究它对湍流传递和扩散的影响。这是因为即使只有一个有效标量，系统也非常复杂。在这项研究中，我们使用RDT，并获得了两个活动标量的解决方案。特别注意的是（1）分子扩散的差异，（2）垂直温度梯度和垂直浓度梯度，（3）垂直平均剪切，（4）分层旋转湍流的固有波模式的影响。我们进一步开发了一个数值程序的热量和标量的传输，并研究了机制，并检查从理论和数值模拟的角度来看的定量结果。理论计算结果与DNS和实验结果吻合较好。这表明，在海洋内部远离表面和底部斜坡（例如，在湍流强度相对较弱的深海中，线性效应很重要。

Multiple diffusion of heat and scalars in stratified rotating turbulence have been studied by RDT (rapid distortion theory), direct numerical simulation (RDT) and turbulent vortex-wave model. In the previous studies, double diffusion problem has been studied as a stability problem of fluid motion and its effects on turbulent transfer and diffusion have not been studied. This is because the system is very complex even with a single active scalar. In this study we have used RDT and obtained the solution for two active scalars. Particular attention is paid to the effects of (1) the difference of molecular diffusion, (2) vertical temperature gradient and vertical concentration gradient, (3)vertical mean shear, (4)the wave mode intrinsic to stratified rotating turbulence. We have further developed a numerical code for the transport of heat and scalar, and investigated the mechanisms and examined the quantitative results from the view point of both the theory and the numerical simulations. The results of the theory (RDT) gave good agreement with the results of DNS and experiments. This shows that in the ocean interior away from the surface and the bottom slope (e.g., abyssal ocean) where the strength of turbulence is relatively weak, linear effects are important.