Collaborative Research: Double-diffusive sedimentation

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CBET 1438052/1437275This project will use theory, numerical simulation, and experiments to study the motion that is induced by instabilities in stratified liquid systems. For example, when fresh water from a river enters the ocean, concentration gradients of sediment and salt form simultaneously. Under certain conditions that can be predicted theoretically, the presence of these gradients leads to an unstable situation that induces convective motion of the sediment-laden water. Preliminary results show that this motion strongly affects the settling velocity and transport of the sediment. This project will develop a framework for analyzing motions induced by such instabilities in a variety of situations pertaining to river estuaries. However, the framework will be more broadly applicable to problems in environmental, geophysical, astrophysical, and engineering flows. This collaborative project will use theoretical, computational, and experimental tools to explore the linear and nonlinear dynamics of double diffusive sedimentation under a wide range of conditions. Linear stability theory, direct numerical simulation, and laboratory experiments will be conducted for four basic configurations: a) a layer of sediment-laden fresh water above saline water; b) a layer of sediment-laden fresh water below saline water; c) linear concentration gradients with sediment being unstably stratified; d) linear concentration gradients with sediment being stably stratified. Effects of shear flow in the water, which is appropriate for river estuaries, will be included. The research will address a range of interesting phenomena observed in these systems including fingering instabilities, horizontal intrusions, and staircases formed in particulate systems. The proposed research will identify dominant instability mechanisms in various parameter regimes, and will provide quantitative scaling laws for double diffusive sedimentation in each case.