CAREER: Stratified Mixing in Sheared and Zero-Mean-Shear Turbulent Environments

在存在相互作用的高能湍流源的流动中，质量输运和混合发生的机制仍然有待于很好地理解。该项目的主要目的是评估在存在密度分层的情况下，平均剪切应力（即由单向流中的速度梯度产生的）与由混沌湍流产生的瞬时和局部剪切应力之间的相互作用所发生的各种类型的质量传输。这项工作的发现将提高对深海混合、海湾或冰下湖泊中的盐水排放、河流中的盐水入侵和雪崩等问题的理解。这项工作将包括通过支持STEM领域女性的“与工程专业本科生有联系的毕业生”计划，对一名研究生和本科生研究人员进行指导。PI将通过艺术展览和教育模块围绕环境混合过程开发大规模的公众参与活动。此外，研究小组将与当地科学博物馆合作，为K-12家庭教育的学生开发一个永久性展览和一个动手实验室研讨会，以研究重力流;从这些实验中产生的数据将与研究界分享。本研究的首要目标是全面评估的独立和综合作用的充满活力的湍流与电流产生的剪切作用在密度分层流体系统。这将通过一个全面的实验室方法来实现，使用独特的和高度可控的设施，允许充分量化流动能量，浮力和流体性质与混合和质量传输动力学之间的联系。三种不同的流动方案将被考虑：湍流没有平均电流，密度电流释放到流体与背景湍流，和平流湍流的密度接口。非侵入性定量成像技术将用于测量速度和质量浓度场，以表征流动动力学。这种系统的方法将提供一个如何竞争的湍流源有助于混合和运输的理解，特别是当剪切驱动流与背景湍流一起作用。预计影响将是深远的，并有直接和实际的手段来落实通过实验室和综合工作获得的科学知识。此外，通过旨在使妇女和在家接受教育的K-12学生与一般公众沿着参与的补充教育和公共宣传活动，预计将取得重大成果。这些活动将在整个提案期内每年进行评估，以促进STEM的公平性，多样性和包容性的持续改善。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Mechanisms by which mass transport and mixing occur remain to be well-understood in flows for which there are interacting sources of energetic turbulence. The primary aim of this project is to evaluate various types of mass transport that occur from the interaction between mean shear stress (i.e. generated by velocity gradients in unidirectional flow) and instantaneous and localized shear stress generated by chaotic turbulence in the presence of density stratification. Findings from this work will improve understanding of deep ocean mixing, brine discharges in bays or subglacial lakes, saltwater intrusions in rivers, and avalanches, among others. The work will include mentorship of a graduate student and undergraduate researchers through the Graduates Linked with Undergraduates in Engineering program that supports women in STEM. The PI will develop large-scale public engagement events surrounding environmental mixing processes through art exhibits and educational modules. Further, the research team will partner with a local science museum to develop a permanent exhibit as well as a hands-on laboratory workshop for K-12 home-schooled students to study gravity currents; data generated from these experiments will be shared with the research community. The overarching goal of this research is to comprehensively evaluate the independent and combined roles of energetic turbulent flows with and without current-generated shear acting upon density-stratified fluid systems. This will be achieved via a comprehensive laboratory approach using unique and highly controllable facilities that allow full quantification of links between flow energetics, buoyancy, and fluid properties with mixing and mass transport dynamics. Three distinct flow scenarios will be considered: turbulence with no mean current, a density current released into fluid with background turbulence, and advection of turbulence over a density interface. Non-invasive quantitative imaging techniques will be used to measure velocity and mass concentration fields to characterize flow dynamics. This systematic approach will provide an understanding of how competing sources of turbulence contribute to mixing and transport, particularly when shear-driven flows act in conjunction with background turbulence. Impacts are expected to be far-reaching, with direct and practical means for implementing the scientific knowledge gained through the laboratory and synthesis efforts. Additionally, significant outcomes are expected via the complementary educational and public outreach activities designed to engage women and home-schooled K-12 students, along with the general public. These activities will be assessed annually throughout the duration of the proposal period to foster continued improvement of equity, diversity, and inclusivity in STEM.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.