This research seeks to understand and quantify the interaction between a gravity current on an inclined slope and a series of incoming internal waves propagating in a two-layer stratified fluid. The objective will be pursued primarily using laboratory experiments, and the results will be contextualized by comparison with numerical simulations and field measurements. Both gravity currents and breaking internal waves are common in the near-coastal ocean. The mixing of the fluid and material carried by the gravity current is a key process in understanding how the land and sea are coupled. There is also a pressing current need to understand this mixing process in more detail due to increasing pressure globally to adopt seawater desalination as a hedge against future freshwater scarcity. These coastal desalination plants discharge highly dense brine effluent into the ocean, where it is assumed to mix with the receiving ocean waters. However, current models of this mixing process typically neglect flow in the coastal ocean, leading to wildly incorrect estimates of the mixing and thus the environmental impact of these effluents. This project will provide the basic science needed to close this knowledge gap and improve these models. The results of this project will be of key interest to engineers and policymakers involved in designing and permitting coastal facilities such as desalination plants the discharge effluents into the near-coastal ocean. The results of this research will be communicated to relevant stakeholders by interacting with colleagues engaged in translational activities at Stanford. The project will contribute to education by supporting a young researcher through the end of his Ph.D. studies and introducing Masters students to research in environmental and geophysical flows. Finally, outreach activities will be pursued via programs run through the Bob and Norma Street Environmental Fluid Mechanics Laboratory.
In the experiments, a constant-flux gravity current will flow down a slope into a two-layer stratified ambient fluid. At the same time, multiple progressive internal waves propagating on the pycnocline will interact with the gravity current, changing the way it mixes into the ambient fluid. The changes to the fate of the gravity-current fluid and the way it mixes into the ambient fluid will be measured with a combination of dye imaging and quantitative planar laser-induced fluorescence. Experiments will be performed for a wide range of relevant gravity-current Richardson numbers and internal wave Froude numbers.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
