Turbulence and Mixing in Stratified Flows
The flow of a dense fluid along a sloping bottom is a basic geophysical process in scenarios ranging from deep ocean outflows to downslope mountain winds. Gravity currents also provide an important mechanism for the transfer of sediments. The establishment of these flows in many cases derives from a region of hydraulic control due to geometric constriction, which generates selective acceleration of the stratified fluid. This acceleration, in turn, destabilizes the flow to shear instabilities that result in turbulent mixing and transfer of mass and momentum.
Laboratory experiments carried out with Larry Armi at Scripps Institution of Oceanography examined the mixing and entrainment mechanisms at the shear interface of a developing downslope current. These revealed an initial, unstable region characterized by rapid development, low shear Richardson numbers and high entrainment. A subsequent high Richardson number region is characterized by weak entrainment and collapsing turbulence.
Density gradient field with density and velocity
profiles for downslope current vs. alongslope distance
Vortex Dynamics in spatially accelerating shear
Realtime and vorticity field images of instability in
accelerating shear flow.