Turbulence in the Inner Part of a Combined Wave-Current Coastal Bottom Boundary Layer

组合波流沿岸底部边界层内部的湍流

• 批准号: 1031040
• 负责人: Joseph Katz
• 金额: $ 51.75万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1031040&HistoricalAwards=false
• 关键词: Turbulence; Inner; Part; Combined; Wave

This project extends efforts by the same team to measure the flow structure and turbulence in the bottom boundary layer (BBL) of the coastal ocean, and study their dependence on circulation, wave field and bottom topography. In-situ measurements have been performed using Particle Image Velocimetry (PIV), which provides time series of 2-D velocity distributions in two independent sample areas, at an unprecedented resolution of 3.5 Kolmogorov scales. Data from other sensors, including an ADV, are also available. Analysis of large datasets obtained in the inner part of the BBL provides profiles of mean velocity, Reynolds shear stress, shear production and dissipation rates, energy spectra, and abundance of eddies. Analysis shows that an inflection point develops in the mean velocity profile, which indicates flow instability, below the mean current log layer, but well above the bottom ripples. Several arguments, including distortion of wave induced velocity, suggest that this inflection develops at the interface between current and thinner wave boundary layer (WBL) below it. Scaling of mean velocity with shear velocity and roughness scales is effective only above the inflection point. Associated instabilities are manifested by a shear production peak at much higher elevations than those in steady rough-wall boundary layers, as well as a rapid increase in the number of small-scale eddies. The latter increases the dissipation rate and modifies the energy spectra. Transition between current and wave boundary layers also involves broad Reynolds stress peaks and shear production exceeding the dissipation rate.This project focuses on elucidating the flow and turbulence near the inflection point, as well as on turbulence generated by interactions of flow and waves with roughness within the WBL. Relying initially on available data, and subsequently on extensive, but selective additional in situ data that will be obtained, the study will address the following questions: (1) Are the inflection, associated instabilities and high turbulence persistent characteristic features of current-WBL interfaces? (2) How are the inflection and associated Reynolds stresses, production and dissipation rates affected by combinations of mean current, wave-induced motion (amplitude, excursion and direction relative to current) and bottom topography? (3) In laboratory steady boundary layers and in canopy flows, turbulence production peaks very near the interface with roughness elements. The question is whether such an interfacial turbulence production peak exists also within the WBL, in addition to the inflection point peak. (4) What are the characteristic strength, scale and abundance of eddies generated by interactions with roughness? How are they related to the current-wave-bottom scales? Do they affect the scale of eddies populating the inflection area and rest of BBL? How do they affect the turbulence statistics? Do these eddies differ from structures populating steady rough wall boundary layers, and what is the implication of these differences?In order to provide a meaningful picture on current-waves-turbulence interactions in the coastal BBL, including the above questions, it is essential to obtain and analyze a substantial database at varying Reynolds numbers, ratios of mean current to wave amplitude, orientation of waves relative to mean current, and orientation of both relative to bottom ripples. Consequently, the available database will be extended during two field deployments in several sites along the Atlantic Continental Shelf. These experiments will feature alignment of one PIV plane with mean current and the other one with waves or roughness as well detailed acoustic mapping of the local bottom roughness.Broader impact: Proper modeling of turbulence in the BBL is essential for predictions of oceanic circulation, climate and weather, as well as transport of pollutants, nutrients and sediment and associated biological processes in coastal waters. The combination of waves, currents and roughness makes modeling of the BBL particularly challenging. Analysis of data obtained by state-of-the-art instruments is an essential step in development of modeling tools.Education of future Scientists: This project will support two graduate (PhD) students, who will be broadly trained in oceanography, fluid mechanics, optics and instrumentation. Undergraduate students will continue to be involved extensively in field trips, subsequent analysis and publications, as a proven means of motivating them to pursue careers in oceanography. The team will also continue the long-term custom of engaging senior high-school students from a neighboring school (Baltimore Polytechnic) in a yearlong, research practicum project, which is part of their required curriculum.

该项目扩展了同一团队的努力，以测量沿海海洋底部边界层（BBL）的流动结构和湍流，并研究了它们对循环，波场和底部地形的依赖。已经使用粒子图像速度法（PIV）进行了原位测量，该测量法（PIV）在两个独立的样本区域中提供了2-D速度分布的时间序列，以3.5 kolmogorov量表的前所未有的分辨率。还提供来自其他传感器（包括ADV）的数据。对BBL内部获得的大型数据集的分析提供了平均速度，雷诺剪切应力，剪切产生和耗散速率，能量光谱以及涡流的丰度。分析表明，在平均速度曲线中会出现拐点，这表明流动不稳定，低于平均电流对数层，但远高于底部波纹。几个参数，包括波浪诱导速度的变形，表明这种拐点在其下方的电流和薄波边界层（WBL）之间发展。剪切速度和粗糙度尺度的平均速度缩放仅在拐点以上有效。相关的不稳定性是由剪切产生峰值在高度要高的剪切​​产量峰值上表现出来的，而在稳定的粗壁边界层中，以及小规模涡流的数量迅速增加。后者增加了耗散速率并修改了能量光谱。电流和波边界层之间的过渡还涉及广泛的雷诺应力峰值和剪切产生超过耗散速率。该项目的重点是阐明拐点附近的流量和湍流，以及由WBL内部与粗糙度的流量和波浪相互作用所产生的湍流。最初依靠可用的数据，随后依靠广泛但有选择性的额外原位数据，该研究将解决以下问题：（1）（1）拐点，相关的不稳定性和高湍流持续的当前WBL接口的特征吗？ （2）如何受到平均电流，波动诱导运动（相对于当前的振幅，偏移和方向）和底部形象的组合影响的拐点和相关的雷诺应力，产量和耗散率？ （3）在实验室稳定边界层和冠层流中，湍流产生的峰值非常接近界面，具有粗糙度元素。问题是，除了拐点峰外，这种界面湍流产生峰是否也存在。 （4）与粗糙度相互作用产生的涡流的特征强度，规模和丰度是什么？它们与当前波底量表有何关系？它们会影响散居拐角区域和其余BBL的涡流规模吗？它们如何影响湍流统计数据？这些涡流是否不同于构成稳定粗糙的壁界层的结构，这些差异的含义是什么？为了在沿海BBL中提供有意义的图片，在沿海BBL中的当前波动驱动相互作用（包括上述问题）（包括上述问题），对于在各种雷诺（Reynolds over）相对且相对相对的比例相对的比例和相对的比例相对均为均值，并且要在各种问题上获得和分析一个实质性的数据库，并且是必不可少的。涟漪。因此，可用的数据库将在大西洋大陆架沿线的几个站点的两个现场部署期间扩展。这些实验将以平均电流为单位的一个PIV平面，而另一个PIV平面则具有波浪或粗糙度，以及局部底部粗糙度的详细声学映射。BBL的影响：BBL中湍流的正确建模对于预测海洋循环，气候和天气以及污染物，营养物质和相关的Bioloticate and Coality Bioloity Processes in Coastal Waters中的海洋循环，气候和天气是至关重要的。波浪，电流和粗糙度的结合使BBL的建模特别具有挑战性。通过最先进的仪器获得的数据分析是开发建模工具的重要步骤。未来科学家的教育：该项目将支持两名研究生（PHD）学生，他们将在海洋学，流体力学，光学和仪器方面接受广泛的培训。本科生将继续广泛参与实地考察，随后的分析和出版物，这是一种激励他们从事海洋学职业的行为手段。该团队还将继续进行长期的习俗，即与一年的研究实习项目与来自邻近学校（巴尔的摩理工学院）的高中生（巴尔的摩理工学院）的高中生订婚，这是他们所需课程的一部分。