Collaborative Research: DNS and high resolution measurements of scalar transfer across an air-water interface during inception and growth of Langmuir circulation

合作研究：朗缪尔环流起始和增长过程中空气-水界面标量传递的 DNS 和高分辨率测量

• 批准号: 1235039
• 负责人: Andres Tejada-Martinez
• 金额: $ 32.41万
• 依托单位: University of South Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-15 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1235039&HistoricalAwards=false
• 关键词: Collaborative; Research; DNS; resolution; measurements; Collaborative; Research; DNS; resolution; measurements

The overarching goal of this study is to characterize the effect of small scale Langmuir turbulence on the temperature of the commonly occurring cool thermal molecular boundary layer (i.e. the cool skin) beneath the air-sea interface and on slightly soluble gas exchange rate across the interface. When wind blows over an initially quiescent air-sea interface, it first generates short capillary waves which in time coexist with longer waves as part of a broad spectrum of waves. The interaction between the wind-driven waves and shear current leads to Langmuir turbulence characterized by Langmuir circulation (LC) consisting of counter rotating vortices roughly aligned in the direction of the wind. The typical length scale of the vortices ranges from several centimeters when short capillary waves first appear up to tens of meters when the spectrum of waves broadens. The centimeter-scale LC are generated very quickly with the gustiness in the wind field (and disappear very quickly as well), thereby providing, over intermittent and repeated gust events, very intense turbulent bursts at the surface which may very well dominate the average surface renewal processes. These renewal events are critical to our understanding of air-sea scalar fluxes. To date, direct numerical simulations (DNS) of small scale LC and its evolution has not been made and measurements of surface renewal time scales and other parameters influenced by these coherent structures have not been performed. Accordingly, this study, based on fine-scale DNS computations along with high resolution laboratory experiments, will capture the growth stages of LC and transition to Langmuir turbulence during the wave aging process. Simulations validated with the experiments will address the following major questions: 1. What is the influence of small scale LC on scalar air-sea fluxes during the early stages of LC development when wind shear is dominant over wave orbital velocities? 2. What is the impact of micro-breaking waves on the structure of small scale LC? 3. What is the cumulative effect of small scale LC and micro-breakers on sea surface molecular layers? 4. What is the structure of LC and the effect of LC on molecular layers during later stages of LC development as LC and surface wave spectra broaden? The experiments will focus on the generation and evolution of small scale LC. They will aim at 1. Assessing the structure, evolution, and stability of small scale Langmuir circulations. 2. Evaluating the impact of these structures on the cool skin with potential influence on the air-sea heat and gas flux. 3. Collecting high quality dynamics measurements within the water column for comparison with the computations. It is anticipated that the LC will impact the cool skin temperature and gas concentration molecular layer by enhancing the surface renewal mechanism, often invoked in parameterizations of the cool skin and gas transfer velocity (a measure of gas transfer efficiency across the air-sea interface). Accordingly, the DNS solver to be used is equipped with an interface capturing technique yielding resolved surface molecular layers, and accurate resolution of violent free-surface motions. The experiments will include PIV and active infrared radiometry yielding direct estimates of sub-surface and surface kinematics. This combined numerical/experimental approach will likely lead to new physical insights into the fine scale processes which control the air-sea molecular fluxes of heat and gas. Broader Impacts: Broad impacts will be made through enhanced fundamental understanding of the fine-scale physics characterizing the ocean cool skin and gas transfer across the air-sea interface in the presence of LC. LC is known to appear and disappear quickly at the ocean surface and plays an important role in global air-sea scalar fluxes. Understanding the influence of LC would allow scientists to develop improved parameterizations of global ocean flux uptake of greenhouse gases such as CO2. Furthermore, results obtained would benefit scientists making estimates of bulk ocean temperatures based on satellite infrared measurements while having to account for the cool skin. Results from this research will be disseminated in journal publications and conferences, and, where appropriate, more popular avenues of publication. At a local level, knowledge gained through this research effort will be incorporated into the education and training of students. The PIs will continue their efforts to promote science and research to a broader audience (K-12 and public) through laboratory visits and informational scientific talks to the public.

这项研究的总体目标是表征小规模的Langmuir湍流对空气界面下通常凉爽的热分子边界层（即凉爽的皮肤）的温度以及对整个界面上略有溶解的气体汇率的影响。当风在最初静止的空气接口上吹来时，它首先会产生短毛细管波，随着时间的流逝，与较长的波相交，作为广泛波的一部分。风驱动的波和剪切电流之间的相互作用导致Langmuir湍流，其特征在于Langmuir循环（LC），这些循环（LC）由大约在风方向上对齐的反旋转涡流组成。涡旋的典型长度范围从短时间毛细管波首先出现到数十米时的典型长度范围，当波频谱扩大时。厘米尺度的LC非常快速地产生，风场的阵风（并且也很快消失），从而提供了间歇性和重复的阵风事件，表面上非常强烈的湍流突发，这很可能很好地统治了平均平均表面更新过程。这些更新事件对于我们对空气标量通量的理解至关重要。迄今为止，尚未进行小尺度LC及其演化的直接数值模拟（DNS），并且尚未执行表面更新时间尺度和其他受这些相干结构影响的参数的测量。因此，这项研究基于精细的DNS计算以及高分辨率实验室实验，将捕获LC的生长阶段，并在波动衰老过程中过渡到Langmuir湍流。通过实验验证的模拟将解决以下主要问题：1。当风剪在波轨道速度上占主导地位时，小规模LC对LC发育早期阶段的标量空气通量的影响是什么？ 2。微裂波对小规模LC结构有什么影响？ 3。小规模LC和微损伤对海面分子层的累积影响是什么？ 4。在LC发育的后期，LC的结构和LC对分子层的影响是什么？实验将集中于小规模LC的产生和演变。他们将以1的目标为目标。评估小规模Langmuir循环的结构，演变和稳定性。 2。评估这些结构对凉爽皮肤的影响，并可能影响空气热和气体通量。 3.在水柱中收集高质量的动力学测量，以与计算进行比较。可以预计，LC将通过增强表面更新机制来影响凉爽的皮肤温度和气体浓度分子层，这通常是在凉爽的皮肤和气体传递速度的参数中引用的（跨空气接口的气体传递效率的度量）。因此，要使用的DNS求解器配备了一种捕获技术，可提供分辨的表面分子层，并准确地解决了暴力自由表面运动。该实验将包括PIV和主动红外辐射指定，从而产生地下和表面运动学的直接估计。这种组合的数值/实验方法可能会导致对控制热量和气体的空气分子通量的精细尺度过程的新物理见解。更广泛的影响：将通过增强对在LC存在下的海洋凉爽皮肤和气体转移来表征海洋凉爽的皮肤和气体转移的细小物理学的基本理解来产生广泛的影响。众所周知，LC在海面出现并迅速消失，并在全球空气标量通量中起重要作用。了解LC的影响将使科学家能够开发出对全球海洋通量吸收温室气体（如CO2）的改进的参数化。此外，获得的结果将使科学家受益于基于卫星红外测量的大量海洋温度的估计，同时必须考虑凉爽的皮肤。这项研究的结果将在期刊出版物和会议上传播，并且在适当的情况下，出版物的出版物途径更为流行。在地方一级，通过这项研究的知识将纳入学生的教育和培训中。 PI将通过实验室访问和向公众的信息科学谈判来继续他们的努力，向更广泛的受众（K-12和公众）促进科学和研究。