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

本文采用快速畸变理论（RDT）求解了分层剪切湍流，研究了剪切对湍流的影响，包括对流换热和垂直换热。通过寻求解析短时近似和任意时刻解的数值计算，阐明了动能谱和热量谱对垂直热通量的影响，包括逆梯度热通量现象。特别注意的事实是，有两个时间尺度在分层剪切湍流，我们已经表明如何确定的剪切和浮力频率的两个时间尺度影响湍流。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决定了随后的能量分配。总体结果同意与DNS低弗劳德数（强烈分层）流。例如，分层剪切湍流的许多特性，如“持续”的反梯度通量，已经被这个线性理论解释。对于层结剪切湍流中的被动标量输送，我们研究了被动标量谱对垂直输送的影响，包括对反梯度输送的影响。

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.