Turbulent Exchanges, Energetics and Transports in Buoyant Gravity Currents

浮力重力流中的湍流交换、能量和传输

• 批准号: 1131621
• 负责人: Jonathan Nash
• 金额: $ 39.14万
• 依托单位: Oregon State University
• 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: 2011-10-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1131621&HistoricalAwards=false
• 关键词: Turbulent; Exchanges; Energetics; Transports; Buoyant

Intellectual Merit: The front that bounds a tidal river plume represents a region of intense exchange between terrestrial- and oceanic-source waters. It propagates as a gravity current, with a turbulent rotor that both dissipates and radiates internal wave energy as it advects and diffuses freshwater into the coastal waters. White and Helfrich (2008) have outlined a framework in which the dissipative or radiative character of a steady front can be assessed from its density and velocity alone, contrasting the hypothesis that frontal deceleration was necessary for wave release (Nash and Moum, 2005). It is the objective of this project to detail the relationship between waves and turbulence using data from the Columbia River plume system, to test some of White and Helfrich?s (2008) ideas in the field, to connect these with laboratory and numerical experiments, and to extrapolate these to a plume-wide system,.The study focuses on 4 aspects of the plume system in which high-resolution turbulence and internal wave data have been collected but not fully analyzed:(1) Energetics and structure of the gravity current head: are details of the density/velocity structure behind the front sufficient to assess whether a front dissipates energy via turbulence or via radiated waves? And can the combination of dissipation, wave trapping and wave release account for the front?s observed evolution (growth and decay)?(2) How do these work to set mass transport and circulation patterns within the head? How/where are energy and mass transported during wave release?(3) Can mixing within the stratified shear flow behind the front be predicted a priori, and how important is it compared to that at the front, from a perspective of both energetics and cross- isopycnal transport?(4) Can (1-3) be related to the external parameters, such as river flow, tides, coastal currents?In addition to testing lab/numerics-inspired theoretical ideas about gravity current propagation, a complimentary goal is to assess which of the front or the trailing shear flow is responsible for the majority of the plume mixing. This is fundamental, as it dictates whether surface coastal waters or deeper fluid is entrained into the plume, which have important biogeochemical consequences. In addition, if energy is lost from the front via waves, that energy is not available for local mixing but may instead produce turbulence in regions remote from the plume itself.Broader Impacts: In addition to the analyses of Columbia River plume data outlined above, a second objective is to link recent fieldwork on plumes of different scale to each other, and to laboratory and numerical studies that are simultaneously being conducted. To do this, a 4-day workshop will be held with a focus on providing a flexible and adaptive forum for discussing recent results, exchanging analysis techniques, and collectively synthesizing studies and future directions. Given that there has been a significant recent interest in this area (with numerous current and recently-completed experiments), such a meeting is timely.This grant will support a PhD candidate at OSU, and provide opportunities for student exchanges among synergistic field/lab/numerical projects. Results will be broadly disseminated in scientific journals and made accessible to the public through the web and other media (newspaper articles, etc.)Finally, knowledge of the location and intensity of plume fronts and of large-amplitude waves is of significant interest to the marine community: (1) for navigation, these are a hazard due to velocity convergence and wave steepening, especially over the bar, (2) for fisherman, they represent active feeding grounds, (3) for pollution response, the front represents both a material boundary for surface contaminants, but also a conduit for exchange into deeper/coastal waters. It is hoped that these results will ultimately improve the skill of operational river-plume models.

学术价值：以潮汐河流羽流为边界的锋面代表了陆地和海洋来源水域之间强烈交换的区域。它以重力流的形式传播，带有一个湍流转子，当它平流并将淡水扩散到沿海水域时，该转子既耗散又辐射内波能量。White和Helfrich(2008)概述了一个框架，在该框架中，稳定锋的耗散或辐射特性可以仅从其密度和速度来评估，这与锋面减速对于波的释放是必要的假设形成了对比(Nash和Moum，2005)。这个项目的目标是利用哥伦比亚河羽流系统的数据详细描述波浪和湍流之间的关系，在野外检验怀特和赫尔夫里奇？S(2008)的一些想法，将这些与实验室和数值实验相联系，并将其外推到整个羽流系统。研究重点放在已经收集了高分辨率湍流和内波数据但没有完全分析的羽流系统的四个方面：(1)重力流头部的能量和结构：锋面后面的密度/速度结构的细节是否足以评估锋面是通过湍流还是通过辐射波来耗散能量？耗散、波捕获和波释放的组合能解释锋面吗？S观察到了演化(生长和衰变)？(2)这些是如何在头部内设定质量传输和环流模式的？在波浪释放过程中能量和质量是如何传递的？(3)从能量学和跨等轴线输送的角度，可以预先预测锋后层状剪切流中的混合吗？(4)(1-3)是否与外部参数有关，如河流水流、潮汐、沿岸流？除了检验实验室/数值激发的关于重力流传播的理论观点外，还有一个补充目标是评估羽流混合的主要原因是锋面或尾部剪切流中的哪一个。这是根本的，因为它决定了是表层沿海水域还是更深的流体被带入羽流中，这会产生重要的生物地球化学后果。此外，如果能量通过波从锋面损失，这些能量不能用于局部混合，而是可能在远离羽流本身的区域产生湍流。广泛影响：除了上面概述的哥伦比亚河羽流数据分析外，第二个目标是将最近关于不同尺度羽流的实地工作彼此联系起来，并将同时进行的实验室和数值研究联系起来。为此，将举行为期4天的研讨会，重点是提供一个灵活和适应性的论坛，讨论最近的结果，交流分析技术，并集体综合研究和未来方向。鉴于最近对这一领域有很大的兴趣(有许多当前和最近完成的实验)，这样的会议是及时的。这项资助将支持俄亥俄州立大学的一名博士生，并为协同领域/实验室/数值项目之间的学生交流提供机会。结果将在科学期刊上广泛传播，并通过网络和其他媒体(报纸文章等)向公众公布。最后，关于羽状锋和大振幅波的位置和强度的知识引起海洋界的重大兴趣：(1)对于航行，这是由于速度会聚和波浪变陡造成的危险，特别是在沙洲上；(2)对渔民来说，它们是活跃的觅食地；(3)对于污染反应，锋面既是表层污染物的物质边界，也是交换到更深/沿海水域的管道。人们希望，这些结果最终将提高河流羽流模型的操作技能。