Direct numerical simulation and linear processes of stably stratified sheared turbulence

Abstract

The stably-stratified turbulence with mean shear is investigated by direct numerical simulation, and the applicability of a rapid distortion theory (RDT) is examined. In this turbulence, the effects of stratification and shear are most significant at large scales, but the stratification is effective down to the Ozmidov scale, and the mean-shear is effective down to the Corrsin scale. Since the stratification and mean shear have linear effects on the governing equations, the RDT, which is a linear theory, applies well down to the Ozmidov or Corrsin scale. The DNS results also show that the mean shear excites the large-scale motion and suppresses the small-scale vertical motion, leading to a better applicability of RDT even at small scales.