| Mixing and transport in stratified flows depends on the strength of turbulence, stratification, and shear. Interactions between turbulence and mean fields are studied with numerical, theoretical and laboratory experiments. The main goal is to understand the effects of shear because the shear effects result in different energetics, mixing, and transport rates. Two flows are considered: turbulence generated from initial buoyancy fluctuations and salt fingers.; The energy evolution in buoyancy-generated turbulence depends on the gradient Richardson number Ri and the stratification number St, which compares the time scale of the initial buoyancy fluctuations to the time scale of the mean field. In the initial period, turbulence energy in all cases grows more than the unsheared case. However, as turbulence evolves with time, shear depletes the energy in weakly sheared cases of both stratified conditions considered. When much energy is supplied to the turbulence field from shear, turbulent kinetic energy increases with time. For subcritical flow, RDT predicts the flow evolution, including energy depletion, well for a wide range of Richardson numbers.; Linear theory and laboratory experiments on a finger-favorable gravity current are applied to study turbulence in a salt finger favorable flow. The theory reproduces well previous observations for unsheared flow, and it predicts that heat can be transported more efficiently than salt, even in salt finger favorable conditions. Effects of shear on the flux ratio are small. The laboratory experiment also produces results similar to the linear theory. Even though the bulk mixing rate increases as the density ratio decreases, the heat flux is larger than the salt flux, and no strong signature of salt fingers was detected. Eddy diffusivities are estimated from control volume analysis and oceanographic microstructure methods. |
