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

环境湍流受空气或水密度分层、剪切运动、内波和湍流之间的复杂相互作用的强烈影响。这种流动可以归类为切变稳定分层湍流(Ssst)。了解Ssst对于一系列环境问题至关重要，例如准确描述海洋环流模型中的垂直混合，这对气候预测、天气预报、预测污染物在大气中的扩散或有害浮游生物在水系中的繁殖至关重要。然而，关于SST物理学的许多基本问题仍然存在，缺乏健壮的、基于物理学的模型。必须解决这些问题，以便在预测Ssst及其在环境应用中的作用方面取得进展。这项研究将导致对SST基本物理的新发现，并开发用于解决环境流动问题的预测模型。外展和教育活动将包括本科生暑期项目，为K-12儿童提供的令人兴奋和互动的新课程和迷你项目，以及通过与艺术的联系解释动荡和复杂科学的迷人和重要主题的公开讲座。虽然已经对SSST的各个方面进行了调查，但顽固的基本问题仍然存在。当层结和切变都很大时，流动可以由湍流和非湍流运动的斑块组成。这种“斑驳”行为如何与动能和势能级联机制产生/相互作用，以及它对标量和粒子传输的影响，仍然是这里需要面对的前沿。研究的目的是通过新的分析、模式和直接数值模拟，为控制SST中能量级联、间歇、混合效率和粒子传输的基本机制提供变革性的见解。具体目标是-目标1：使用滤波和慢-快流形分解对动能和势能级联机制进行新的分析，以揭示内波、平均切变和非线性的贡献。目标2：对过滤后的流体速度和密度梯度使用新的基于Navier-Stokes的拉格朗日模型，以准确地捕捉非线性项，并且对于任意的雷诺数和普朗特数是稳健的。目标3：开发新的粒子传输模型，扩展和应用目标2的模型来预测多尺度聚集和粒子取向。其中一个本科暑期实习项目将涉及将目标2的模型与天气研究和预报(WRF)模型相结合，以预测WRF未解决的尺度上的湍流，并探索大尺度流动条件变化对这些未解决尺度的影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.