Wave and energy/flux oscillations in rotating stratified turbulence

利用快速扭曲理论得到了层状旋转湍流的解，研究了层结和旋转的联合效应，包括逆梯度热流和垂直换热的影响。通过在RDT的线性框架中寻找精确的解析解，阐明了动能谱和热谱对垂直热流的影响，包括逆梯度热流现象。特别注意了分层旋转湍流中存在两个时间尺度的事实，并说明了由旋转和浮力频率决定的两个时间尺度对湍流的影响。对于低弗劳德数(强分层)流动，总体计算结果与数值模拟结果吻合较好。例如，分层旋转湍流的许多特征，如旋转引起的通量振荡的相移，都可以用这个线性理论来解释。对于分层湍流中的被动标量传输，我们指出了初始条件和湍流的不稳定性的重要性，这些在以往的被动标量扩散研究中常常被忽视。这项研究的结果将有助于未来大气和海洋中湍流扩散的模拟。

Solutions for the stratified rotating turbulence have been obtained by the RDT (rapid distortion theory) to investigate the effects of combined effects of stratification and rotation, including the counter-gradient heat flux and the vertical heat transfer. By looking for the exact analytical solutions in RDT's linear frame work, it has been clarified how the spectra of the kinetic energy and the heat affect the vertical heat flux, including the phenomenon of the counter-gradient heat flux. Particular attention has been paid to the fact that there are two time scales in stratified rotating turbulence and we have shown how the two time scales determined by the rotation and the buoyancy frequency affect the turbulence. The overall results agreed well with the DNS for low Froude number (strongly stratified) flows. For example, many of the characteristics of stratified rotating turbulence, e.g., the phase shift of the flux oscillations due to rotation, has been explained by this linear theory. For the passive scalar transfer in stratified turbulence, we have shown the importance of the initial conditions and the unsteadiness of turbulence which have been often overlooked in the previous study of passive scalar diffusions. The results of this study will be of help in future modeling of turbulent diffusion in the atmosphere and the ocean.