OCE-PRF: Vertical transport of buoyant, non-spherical particles in the wind-mixed ocean surface boundary layer

该奖项全部或部分由2021年美国救援计划法案（公法117-2）资助。海洋表面的颗粒丰富：微生物，冰晶，碎片，微塑料。虽然许多是浮力的，但这些颗粒并不是被动地漂浮在水面上;它们通过风吹过水面产生的湍流在海洋的上部区域不断混合。与小的球形颗粒不同，这些非球形颗粒和有时大的颗粒由于它们的大小和形状而不能完全跟随流体流动，并且它们与海洋表面湍流的相互作用还没有得到很好的理解。PI将进行实验和分析调查，以研究浮力，非球形颗粒如何移动，旋转和分散在海洋表面的风混合过程中。了解这些粒子的行为将在海洋科学中产生深远的应用，从海洋光学到浮游生物学再到海冰动力学。特别是，了解非球形微塑料颗粒的运输对于量化微塑料污染的规模及其对人类健康和环境的风险至关重要。该项目的结果将为未来的政策，健康指南，消费者行为和微塑料去除工作提供信息。此外，PI将通过在大学一级提供指导和参与高中一级的课外活动，努力扩大当地社区对科学的参与。 PI将使用粒子阴影跟踪技术测量实验室风混合表面边界层中非球形粒子的垂直传输和分散。将对一系列与海洋表层有关的粒子几何形状和风速进行实验。这些测量结果将被用来开发一个分析模型的粒子空间分布在水柱。该项目解决了目前对颗粒形状和惯性如何影响风驱动的海洋表层颗粒传输的理解中的一个主要空白。斯托克斯数是一个关键参数，它量化了粒子对湍流流体运动的响应程度，海洋中粒子的范围从零到O（1），但迄今为止，大多数研究都只关注斯托克斯数为零的粒子，这些粒子完美地跟踪流体流动。除了斯托克斯数之外，定义流体-颗粒动力学的其他参数包括可漂浮性参数、非球形颗粒尺寸之间的纵横比和颗粒雷诺数。非球形颗粒在表面边界层的传输跨越了很宽的参数空间，然而，系统的实验研究，在整个这个参数空间尚未完成。一个复杂的因素是，通过湍流的颗粒传输是固有的拉格朗日过程，即，相关的参照系是沿着每个粒子的轨迹沿着每个粒子的参照系。在空间和时间上跟踪颗粒的拉格朗日测量难以在现场获得，并且研究通常在欧拉参考系中描述颗粒传输和垂直浓度场，即，在一个固定的坐标系中。该项目将系统地探索风驱动湍流中非球形、非示踪粒子的参数空间，并将获得粒子浓度、深度和方向的欧拉和拉格朗日统计。该奖项反映了NSF的法定使命，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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Particles at the ocean surface are plentiful: microorganisms, ice crystals, debris, microplastics. Although many are buoyant, these particles do not passively float on the surface of the water; they are continually mixed within the upper regions of the ocean by the turbulence that results from wind blowing over the water surface. Unlike small, spherical particles, these non-spherical and sometimes large particles do not perfectly follow the fluid flow due to their size and shape, and their interaction with turbulence at the ocean surface is not well understood. The PI will conduct an experimental and analytical investigation to study how buoyant, non-spherical particles move, rotate, and disperse during wind-mixing at the surface of the ocean. Knowledge of how these particles behave will have far-reaching applications in ocean science, from ocean optics to plankton biology to sea ice dynamics. In particular, understanding the transport of non-spherical microplastic particles is critical for quantifying both the scale of microplastic pollution and its risks to human health and the environment. The results of this project will inform future policy, health guidelines, consumer behavior, and microplastic removal efforts. In addition, the PI will work to broaden participation in science within the local community through mentoring at the university level and involvement in extracurricular activities at the high school level. The PI will measure vertical transport and dispersion of non-spherical particles in a laboratory wind-mixed surface boundary layer using particle shadow tracking techniques. Experiments will be performed for a range of particle geometries and wind speeds relevant to the ocean surface layer. These measurements will then be used to develop an analytical model of particle spatial distribution over the water column. The project addresses a major gap in the current understanding of how particle shape and inertia affect particle transport in the wind-driven ocean surface layer. The Stokes number, a key parameter which quantifies how responsive a particle is to turbulent fluid motions, of particles in the ocean spans from zero to O(1), but most studies to date have focused only on particles with a Stokes number of zero, which perfectly trace the fluid flow. In addition to the Stokes number, other parameters that define the fluid-particle dynamics include the floatability parameter, the aspect ratio between the dimensions of non-spherical particles, and the particle Reynolds number. Non-spherical particle transport in the surface boundary layer spans a wide parameter space; however, systematic experimental studies throughout this parameter space have not yet been done. A complicating factor is that particle transport by turbulence is an inherently Lagrangian process, i.e., the relevant frame of reference is one that follows each particle along its trajectory. Lagrangian measurements which track particles in space and time are difficult to obtain in situ, and studies often describe particle transport and vertical concentration fields in an Eulerian frame of reference, i.e., within a stationary coordinate system. This project will systematically explore the parameter space of non-spherical, non-tracer particles in wind-driven turbulence and will obtain both Eulerian and Lagrangian statistics of particle concentration, depth, and orientation. The results will provide insights into the physical processes governing a wide range of ocean transport phenomena, including that of microplastic pollution.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.