| Mixing efficiency and nonlinear interactions in stratified turbulence were studied using rapid distortion theory (RDT). Mixing efficiency was predicted in strongly stratified flows for both one and two active scalars. The former used results of Hanazaki and Hunt (1996), while a new analytical solution was derived for the latter. Mixing efficiencies depend on the Schmidt number Sc, Grashof number Gr, and density ratio Rρ. A decrease in the mixing efficiency was observed as Sc increased for the one scalar case and as Rρ decreased for the two scalar case. RDT was also extended in an attempt to better predict behaviors in moderately stratified flows. Extensions using eddy viscosities, simulations, and modification of RDT input parameters were attempted and compared to experimental data, but magnitude and peak timing discrepancies in the vertical flux correlation coefficient curves remained. A different attempt at extending RDT was made by deriving expressions for the neglected nonlinear terms using an approach similar to Kevlahan and Hunt (1997). A model system including the expected form of the nonlinear terms showed that adjustment of coefficients in the nonlinear term had the ability to influence the period and decay of turbulent parameters. |
