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

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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.