Collaborative Research: Swimming and Settling in Stratified Fluids

合作研究：分层流体中的游泳和沉降

• 批准号: 1066545
• 负责人: Arezoo Ardekani
• 金额: $ 22.5万
• 依托单位: University of Notre Dame
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-06-15 至 2014-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1066545&HistoricalAwards=false
• 关键词: Collaborative; Research; Swimming; Settling; Stratified

1066545/1066566Ardenkani/StockerMany aquatic systems are characterized by regions where water density varies over depth, often due to temperature or salinity gradients. These pycnoclines are associated with intense biological activity and can affect carbon fluxes by slowing the descent of particles. The low to moderate Reynolds number regime is particularly important, because the vast majority of organisms and particles are small (µm-cm) and their motion predominantly viscous. Despite this, the fundamental fluid dynamics of settling and swimming in a stratified fluid have remained largely unexplored. This is partly due to the widespread belief that the relevant length scale of stratification is orders of magnitude larger than organisms. The PIs have recently showed this not to be true, and that typical aquatic stratifications can in fact affect the flow field of particles and organisms as small as O(100 ìm). This opens the door to a broad new set of questions on viscous motion in stratified fluids a novel area of fluid mechanics. The proposed research will take first strides into this new area by determining and rationalizing the effects of stratification on swimming organisms and settling of elongated particles through a combination of experimental, theoretical, and computational research. New tools will be developed to solve for the flow field of swimming organisms in stratified fluids and conduct a broad, in-depth investigation on the effects of buoyancy, viscosity, inertia and diffusion on fundamental hydrodynamic parameters, including swimming speed, velocity decay rates and energy expenditure. The proposed research will address the important component of the geometrical complexity of natural particles and organisms, by focusing on the role of elongation on settling. A novel hypothesis is developed in this proposal and will be tested both theoretically and experimentally: that a buoyancy-induced torque reorients elongated particles and considerably affects their descent.During the last few decades, important correlations have been discovered between regions of fluid stratification and a wide range of environmental processes, including algal blooms, accumulation of marine snow particles, and vertical migration of aquatic organisms. Although this is often the realm of aquatic scientists and oceanographers, what is missing is a fundamental understanding of the fluid mechanics in this new, unexplored regime where both stratification and viscous effects are important. This study will yield the first physical insights on the hydrodynamics of this regime within the broad context of particle settling and organism motility. These new insights, along with the state-of-the-art experimental and numerical techniques to be developed, will (i) provide fertile ground for a broad range of other researchers (mathematicians, engineers, oceanographers, limnologists, ecologists) at the interface between fluid mechanics and the aquatic sciences; and (ii) inform a broad range of processes in aquatic ecosystems, of ecological and societal value, for example by contributing to improved management practices to prevent eutrophication (e.g. algal blooms), providing better estimates of particle fluxes for biogeochemical ocean models and furthering the understanding of the fate of oil droplets dispersed from oil plumes in the marine environment. This grant will provide training for three graduate students. The participation of women and members of underrepresented groups will be strongly encouraged through the Women's Engineering Program at Notre Dame and presentations at an all-women's college (Saint Mary's college). The PIs will ensure the participation of undergraduates, particularly in the experimental aspects of the project, through the Undergraduate Research Opportunities Program at both Notre Dame and MIT.

1066545/1066566Ardenkani/Stocker许多水生系统的特点是水密度随深度变化，通常是由于温度或盐度梯度而导致的，这些密度斜层与强烈的生物活动有关，可以通过减慢颗粒的下降来影响碳通量。雷诺数体系尤其重要，因为绝大多数生物体和颗粒都很小（微米-厘米），并且它们的运动主要是粘性的。分层流体中沉降和游动的基本流体动力学在很大程度上仍未被探索，部分原因是人们普遍认为分层的相关长度尺度比生物体大几个数量级。这是真的，并且典型的水生分层实际上可以影响小至 O(100 µm) 的颗粒和生物体的流场，这为解决分层中的粘性运动的一系列广泛的新问题打开了大门。流体是流体力学的一个新领域，该研究将通过实验、理论和计算研究的结合来确定和合理化分层对游泳生物和细长颗粒沉降的影响，从而迈入这一新领域。将开发工具来求解分层流体中游动生物的流场，并对浮力、粘度、惯性和扩散对基本流体动力学参数（包括游动速度、速度衰减率和能量）的影响进行广泛、深入的研究拟议的研究将通过关注伸长对沉降的作用来解决自然颗粒和生物体几何复杂性的重要组成部分，并将在理论上和实验上进行测试：浮力。诱导扭矩重新定向拉长的颗粒并极大地影响它们的下降。在过去的几十年中，人们发现流体分层区域与广泛的环境过程之间存在重要的相关性，包括藻类大量繁殖、海洋雪颗粒的积累以及海洋雪颗粒的垂直迁移。尽管这通常是水生科学家和海洋学家的领域，但缺少的是对这种新的、未经探索的流体力学的基本力学理解，其中分层和粘性效应都很重要。这项研究将产生第一个物理见解。在粒子沉降和有机体运动的广泛背景下研究该体系的流体动力学，这些新见解以及将要开发的最先进的实验和数值技术，将（i）为广泛的研究提供肥沃的基础。流体力学和水生科学之间的一系列其他研究人员（数学家、工程师、海洋学家、湖沼学家、生态学家）；以及 (ii) 为水生生态系统中具有生态和社会价值的广泛过程提供信息，例如通过做出贡献改进管理实践，防止富营养化（例如藻华），为生物地球化学海洋模型提供更好的颗粒通量估计，并进一步了解从石油中分散的油滴的命运这笔赠款将为三名研究生提供培训，通过圣母大学的妇女工程计划和在女子学院（圣玛丽学院）的演讲，大力鼓励妇女和代表性不足的群体成员的参与。 PI 将通过圣母大学和麻省理工学院的本科生研究机会计划确保本科生的参与，特别是在项目的实验方面。