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.

1066545/1066566 Ardenkani/斯托克许多水生系统的特点是水密度随深度变化的区域，通常是由于温度或盐度梯度。这些浓缩线与强烈的生物活动有关，可以通过减缓颗粒的下降来影响碳通量。低雷诺数到中等雷诺数的状态特别重要，因为绝大多数生物体和颗粒都很小（μm-cm），它们的运动主要是粘性的。尽管如此，在分层流体中沉降和游泳的基本流体动力学仍然在很大程度上未被探索。这部分是由于人们普遍认为分层的相关长度尺度比生物大几个数量级。PI最近表明这不是真的，典型的水生分层实际上可以影响小至O（100 μ m）的颗粒和生物的流场。这就打开了一扇大门，一个广泛的新的问题，在分层流体的粘性运动，一个新的领域的流体力学。拟议的研究将通过实验，理论和计算研究相结合，确定和合理化分层对游泳生物和细长颗粒沉降的影响，从而迈出这一新领域的第一步。将开发新的工具，以解决分层流体中游泳生物的流场问题，并广泛深入地研究浮力、粘性、惯性和扩散对基本流体动力学参数的影响，包括游泳速度、速度衰减率和能量消耗。拟议的研究将解决自然颗粒和生物体的几何复杂性的重要组成部分，通过集中在沉降的伸长的作用。一个新的假设是在这个建议，并将在理论和实验上进行测试：浮力引起的扭矩reorients细长颗粒，并大大影响他们的descendation. In过去的几十年中，重要的相关性已被发现之间的区域的流体分层和广泛的环境过程，包括藻华，海洋雪颗粒的积累，和水生生物的垂直迁移。虽然这通常是水产科学家和海洋学家的领域，但缺少的是对这种新的、未经探索的制度中的流体力学的基本理解，在这种制度中，分层和粘性效应都很重要。这项研究将产生第一个物理的洞察力的流体动力学的这一制度在广泛的背景下，颗粒沉降和生物体的运动。这些新的见解，沿着国家的最先进的实验和数值技术的发展，将（i）提供肥沃的土壤，为广泛的其他研究人员（数学家，工程师，海洋学家，湖沼学家，生态学家）在流体力学和水生科学之间的接口;和（ii）告知水生生态系统中的广泛过程，具有生态和社会价值，例如，通过促进改进管理实践来防止富营养化（例如藻华），为海洋地球化学模式提供更好的颗粒通量估计，并进一步了解分散的油滴的命运海洋环境中的石油羽流。这笔赠款将为三名研究生提供培训。将通过圣母大学的妇女工程方案和一所女子学院（圣玛丽学院）的介绍，大力鼓励妇女和代表性不足群体的成员参与。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。