The Effect of Mean Strain on the Stably Stratified Turbulence.

Abstract

The effect of irrotational strain on stably stratified turbulence is investigated using the rapid distortion theory (RDT) which has been newly developed for a variable density gradient. We consider two kinds of strain which correspond to the longitudinally and laterally distorting ducts. We found that the most important parameter is the ratio of the initial Brunt Vailsala frequency to the strain rate. However, time development of the energies and the fluxes have shown that the oscillation period is approximately π/N independent of the strain, showing the dominant role of stratification. Comparison of the RDT results with the experiments also gives good agreement. For example, the strain prevents the decay of vertical kinetic energy, and the vertical buoyancy flux becomes more downgradient. These results show that many of the characteristics of the stratified turbulence with irrotational strain can be explained qualitatively by the linear processes described by RDT.