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.

智力优点：潮汐河羽流的前沿代表了陆地和海洋源水之间激烈交换的区域。它以重力流的形式传播，带有湍流转子，当淡水平流和扩散到沿海水域时，会消散和辐射内部波浪能。 White 和 Helfrich (2008) 概述了一个框架，其中稳定锋面的耗散或辐射特征可以仅根据其密度和速度进行评估，这与锋面减速对于波浪释放是必要的假设形成鲜明对比 (Nash 和 Moum, 2005)。该项目的目标是利用哥伦比亚河羽流系统的数据详细说明波浪和湍流之间的关系，在该领域测试 White 和 Helfrich（2008）的一些想法，将这些与实验室和数值实验联系起来，并将这些结果外推到整个羽流系统。该研究重点关注羽流系统的 4 个方面，其中已收集但尚未完全收集高分辨率湍流和内波数据。 分析：（1）重力流头的能量和结构：锋面后面的密度/速度结构的细节是否足以评估锋面是否通过湍流或通过辐射波耗散能量？耗散、波捕获和波释放的组合能否解释锋面观察到的演化（增长和衰变）？（2）这些如何发挥作用来设定头部内的质量传输和循环模式？波浪释放过程中能量和质量如何/在哪里传输？（3）从能量学和跨等密度传输的角度来看，前沿后面的分层剪切流内的混合是否可以先验预测，与前沿相比有多重要？（4）（1-3）是否可以与外部参数相关，例如河流流量，潮汐，沿岸流？除了测试实验室/数值启发的理论想法之外 重力流传播时，一个补充目标是评估前部或尾部剪切流中的哪一个负责大部分羽流混合。这是至关重要的，因为它决定了地表沿海水域或更深的流体是否被夹带到羽流中，这会产生重要的生物地球化学后果。此外，如果能量通过波浪从前方损失，则该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。更广泛的影响：除了上述对哥伦比亚河羽流数据的分析之外，第二个目标是将最近对不同规模羽流的现场工作相互联系起来，并将其与同时进行的实验室和数值研究联系起来。为此，将举办为期 4 天的研讨会，重点是提供一个灵活且适应性强的论坛，用于讨论最新结果、交流分析技术以及共同综合研究和未来方向。鉴于最近人们对这一领域产生了浓厚的兴趣（有许多当前和最近完成的实验），这样的会议是及时的。这笔赠款将支持俄勒冈州立大学的博士生，并为学生在协同领域/实验室/数值项目之间进行交流提供机会。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）向公众开放。最后，有关羽流锋和大振幅波浪的位置和强度的知识对海洋界具有重大意义：(1) 对于航行来说，这些由于速度收敛和波浪陡峭而造成危险，特别是在海坝上，(2) 对于渔民来说，它们代表了活跃的进食地，(3) 在污染响应中，前沿既代表了表面污染物的物质边界，又代表了进入更深/沿海水域的通道。希望这些结果最终能够提高河流羽流模型的操作技能。