CAREER: Sheared stratified turbulence: novel mechanisms and models of complex wave-vortex interactions that impact our environment

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Environmental turbulent flows are strongly influenced by stratification of air or water density, complex interactions between shearing motions, internal waves, and turbulence. Such flows may be categorized as Sheared, Stably Stratified Turbulence (SSST). Understanding SSST is crucial for a plethora of environmental problems, such as accurately describing vertical mixing in ocean circulation models, which are key for climate predictions, for weather forecasting, for predicting the dispersion of pollutants in the atmosphere or harmful plankton blooms in water systems. However, many fundamental questions about the physics of SSST remain, and robust, physics-based models are lacking. These issues must be addressed in order to make progress in predicting SSST and its role in environmental applications. This research will lead to new discoveries about the fundamental physics of SSST, and the development of predictive models for solving environmental flow problems. Outreach and education activities will include undergraduate summer projects, exciting and interactive new lessons and mini-projects for K-12 children, and public lectures that explain the fascinating and important subjects of turbulence and complexity science through connections with art. While aspects of SSST have been investigated, recalcitrant fundamental questions remain. When both stratification and shear are large, the flow may be composed of patches of turbulent and non-turbulent motion. How this “patchy” behavior originates/interacts with the kinetic and potential energy cascade mechanisms, and its implications for the transport of scalars and particles, remains a frontier to be confronted here. The research objective is to provide transformative insights into the fundamental mechanisms governing the energy cascades, intermittency, mixing efficiency, and particle transport in SSST, through new analysis, models, and Direct Numerical Simulations. Specific goals are - Goal 1: Conduct a new analysis of the kinetic and potential energy cascade mechanisms using filtering and slow-fast manifold decompositions to unravel contributions from internal waves, mean-shear, and nonlinearity. Goal 2: Use new Navier-Stokes-based, Lagrangian models for the filtered fluid velocity and density gradients to capture the nonlinear term exactly and which are robust for arbitrary Reynolds and Prandtl numbers. Goal 3: Develop new models of particle transport, that extend and apply the models of Goal 2 to predict multi-scale clustering and particle orientations. One of the undergraduate summer internship projects will involve coupling the models of Goal 2 to the Weather Research and Forecasting (WRF) model to predict turbulence at scales not resolved by WRF and explore the impact of variations in large-scale flow conditions on these unresolved scales.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.