Collaborative Research: Droplet transport in the vicinity of breaking waves: Experiments and simulations

海洋表面喷雾和气溶胶生成的准确预测对于包括天气和气候预测在内的各种应用至关重要。本研究旨在描述和量化海洋中破碎表面波周围湍流气流中的液滴输送。设计了一种独特的实验和数值相结合的方法。在特拉华州大学的海气相互作用实验室，将再现受控的、可重复的破碎波事件，并将使用不同液滴尺寸的液滴浓度和速度的测量值来直接估计生产通量。在圣母大学，测量的波形和液滴产生速率被用作大涡流模拟的输入，该模拟被配置为重建实验室条件。液滴统计数据之间的实验和模拟直接比较，模拟将提供一种手段，调查动量和热力学交换率，以及放大到现场条件。数值天气和气候模式需要精确的参数化海洋气溶胶源通量，只有通过了解液滴传输后立即生产这些可以忠实地改善。这项研究的结果将用于培训2名博士生和从事STEM学科的本科生。还将通过利用研究材料进行教育推广工作，包括制作图像，向广大受众传播研究结果，该项目提供了关于湍流波边界层中液滴动力学的前所未有的视角。几乎所有的现场观测喷雾生产率推断通量的基础上固定的高度浓度，这一过程需要作出假设的湍流运输的液滴在最低区域的海洋边界层。对于小液滴，这些假设中的许多都成立，但对于大液滴--那些最有可能改变海气热量和动量通量的液滴--诸如液滴惯性、破碎波后的流动分离和优选的波相对喷射位置等因素可能违反假设。该研究计划旨在实现几个具体目标：（一）进行受控实验室实验，为数值模拟提供信息，并对统计数据和总平衡进行一对一的比较;（二）在实验和模拟中直接计算液滴的尺寸分辨垂直通量，以揭示表面波附近不均匀和间歇性湍流的影响;以及（iii）使用大涡流模拟确定液滴的产生/沉积速度并扩展到实际条件。主要成果将包括不同大小的液滴的修正通量剖面关系，以及对喷雾引起的热量、动量和水分通量的更好的知情估计。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

The accurate prediction of spray and aerosol generation at the ocean surface is essential for a wide variety of applications including weather and climate predictions. This research aims at characterizing and quantifying droplet transport in the turbulent airflow around breaking surface waves in the ocean. A unique combined experimental and numerical approach is designed. At the air-sea interaction laboratory at the University of Delaware, controlled, repeatable breaking wave events will be re-produced, and measurements of droplet concentration and velocity for different droplet sizes will be used to directly estimate production fluxes. At the University of Notre Dame, measured waveforms and droplet production rates are used as inputs into large eddy simulations configured to recreate laboratory conditions. Droplet statistics are directly compared between experiments and simulations, and the simulations will provide a means for investigating momentum and thermodynamic exchange rates, as well as upscaling to field conditions. Numerical weather and climate models require accurate parameterizations of marine aerosol source fluxes, and only by understanding droplet transport immediately after production can these be faithfully improved. The results of this study will be used for training 2 PhD students and for engaging undergraduate students in STEM disciplines. The results will also be disseminated to a wide audience through the utilization of the research material for educational outreach efforts, including visualizations.The project provides an unprecedented view of droplet dynamics in the turbulent wave boundary layer. Virtually all field observations of spray production rates infer fluxes based on fixed-height concentrations, and this process requires making assumptions regarding the turbulent transport of droplets in the lowest regions of the marine boundary layer. For small droplets, many of these assumptions hold, but for large droplets - those with the largest potential for altering air-sea heat and momentum fluxes - factors such as droplet inertia, flow separation behind breaking waves, and preferred wave-relative ejection locations likely violate assumptions. The research plan is aimed at several specific objectives: (i) performing controlled laboratory experiments which inform numerical simulations, and making one-to-one comparisons of statistics and bulk balances; (ii) directly compute size-resolved vertical fluxes of droplets in both experiments and simulations, in order to reveal the influence of inhomogeneous and intermittent turbulence in the vicinity of surface waves; and (iii) determine the production/deposition velocity of droplets and expand to realistic conditions using the large eddy simulations. The key outcomes will include modified flux-profile relationships of droplets of varying size, and better-informed estimates of spray-induced fluxes of heat, momentum, and moisture.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.