Vertical mixing in homogeneous sheared stratified turbulence: A one-dimensional-turbulence study
We conduct a parametric study of diapycnal mixing using one-dimensional-turbulence (ODT) simulations. Homogeneous sheared stratified turbulence is considered. ODT simulations reproduce the intermediate and energetic regimes of mixing, in agreement with previous work, but do not capture important physics of the diffusive regime. ODT indicates Kρ~ɛ/N2 for the intermediate regime, and Kρ~(ɛh4)1/3 for the energetic regime and limit of near-zero stratification. Here Kρ is the turbulent diffusivity for mass, ɛ the dissipation rate, N the buoyancy frequency, and h the computational domain height, where h is relevant mainly in simulations with jump-periodic vertical boundary conditions. These scaling relationships suggest that Kρ is independent of the molecular diffusivity. ODT results for a wide range of parameters show that Kρ cannot be parametrized solely with the turbulent intensity parameter ɛ/(νN2), in contrast with the previous studies, but it is well predicted by correlations using the Ellison length scale.