The mechanisms of the heat and mass transfer in stratified sheared turbulence and its controlling method

利用RDT(快速扭曲理论)得到了分层剪切湍流的解，研究了剪切的影响，包括逆梯度热流和垂直换热。通过寻找任意时刻的解析短时近似和解的数值计算，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。特别注意了分层剪切湍流中存在两个时间尺度的事实，并说明了由切变和浮力频率决定的两个时间尺度对湍流的影响。与无剪切结果的比较表明，即使有剪切，动能和势能的初始分配也决定了随后的能量分配。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，分层切变湍流的许多特征，如“持久的”逆梯度通量，都可以用这个线性理论来解释。对于分层切变湍流中的被动标量传输，我们研究了被动标量谱对其垂直传输的影响，包括逆梯度传输。

Solutions for the stratified sheared turbulence has been obtained by the RDT (rapid distortion theory) to investigate the effects of shear, including the counter-gradient heat flux and the vertical heat transfer. By looking for the analytical short-time approximations aud the numerical evaluation of the solution at arbitrary times, 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 sheared turbulence and we have shown how the two time scales determined by the shear and the buoyancy frequency affect the turbulence. Comparison with the no-shear results shows that even with shear, initial partition of the kinetic energy and the potential energy determines the subsequent partition of the energies. The overall results agreed well with the DNS for low Froude number (strongly stratified) flows. For example, many of the characteristics of stratified sheared turbulence, e.g.the 'persistent' counter-gradient flux, has been explained by this linear theory. For the passive scalar transfer in stratified sheared turbulence, we investigated how the passive scalar spectra affect the vertical transfer of them, including the counter-gradient transfer.