Direct Simulation of Homogeneous Turbulence and Gravity Waves in Sheared and Unsheared Stratified Flows

摘要: Differences in the evolution of stably stratified turbulence with and without mean shear are investigated by means direct numerical simulations for moderate Reynolds number (Re l = 42.7) seven values Froude or Richardson number. The molecular Prandtl is unity. In flows shear, energy decays quickly initially but at reduced rate later when gravity waves dominate flow pattern. Gravity occur Ellison length scale reaches about 0.3 to 0.8 times Ozmidov scale. becomes anisotropic before first arise. developed dominated waves, turbulent mixing considerably suppressed, six Kolmogorov For sheared importance buoyancy relative forcing depends on Ri. an initial Sh 0 3, we find a critical 0.13 which smaller than value 0.25 predicted linear viscid theory because rather strong dissipation present simulations. subcritical (Ri Ri crit ), controlled behaves large scales as if no would be present. But causes small-scale (possibly wave breaking) hence larger shear. degree anisotropy increases increasing gets limited counter-gradient fluxes (CGF) heat momentum appear vertical direction. Temporally oscillating sign-changing have distinguished from persistently positive (p-CGF) small scales. Both types develop well unsheared flows. flux exchanges between kinetic potential reservoirs can described rapid-distortion calculations. p-CGF due imbalance sources sinks