An Experimental Investigation of the Effects of Surfactants on the Generation of Droplets by Breaking Wind Waves

智能优点：风浪系统中液滴的产生及其随后的运动和蒸发是空气-水界面上质量、热量和动量转移过程的重要组成部分。这些液滴的分布和大小已经在波浪水槽中和现场进行了测量。众所周知，海洋表面是由表面活性剂单层覆盖的，表面活性剂可以对许多自由表面现象产生重要影响，包括水滴的喷射。拟议的实验室实验的目的是探索通过破碎波形成液滴的机制，以及这些液滴在表面活性剂存在和不存在的情况下随后的运动和蒸发。机械产生的波浪、风浪和有风的机械产生的波浪的实验将在干净的水和混合了不同浓度的几种可溶表面活性剂的水中进行，并在盐水中进行有限的实验。流动和横流破碎波过程的电影激光诱导荧光(LIF)测量，液滴喷射、后续运动和尺寸分布的阴影电影，以及波峰内流场的粒子图像测速(PIV)将从仪器托架中进行，该仪器托架将设置为随破碎波峰或波浪系统的其他重要特征沿水箱移动。还将在波浪水槽中的固定位置测量液滴和液滴通量的垂直分布。水面特性包括表面压力等温线和表面粘弹性特性将使用安装在小水箱中的朗缪尔槽/纵波传播装置和从波浪水箱中采集的水样来测量。此外，还将在波浪槽中使用最大气泡压力法，以确定原位扩散常数和表面张力。最后，将在储罐中的固定位置进行瞬时自由表面活性剂浓度的二次谐波(SHG)测量。所有上述测量将用于探索液滴抛射、运动和蒸发过程的物理过程。更广泛的影响：由于破碎波产生的液滴对海-气转移过程做出了重要贡献，拟议的研究将有助于我们理解气候，包括全球气候变化等重要现象。这项研究的结果将适用于理解涉及自由表面和喷雾产生的工程流动(如船舶周围的流动或化学加工中的流动)。这项研究将通过支持一名研究生、一名本科生和一名兼职博士后研究员，为学生的理科教育做出贡献。PI还将在每学期为当地高中生举办一次约一次讲座或一次实地访问，以向他们介绍本研究的主题领域。希望这能培养他们在大学学习中学习海洋学的兴趣。

Intellectual Merit: The generation of droplets and their subsequent motion and evaporation in wind wave systems are important components of the processes of mass, heat and momentum transfer across the air-water interface. Measurements of the distribution and sizes of these droplets have been made in wave tanks and in the field. It is well known that the ocean surface is covered by surfactant mono-layers and that surfactants can have important effects on many free surface phenomena including the ejection of water droplets. The objective of the proposed laboratory experiments is to explore the mechanism of droplet formation by breaking waves and the subsequent motion and evaporation of these droplets with and without surfactants. Experiments with mechanically generated waves, wind waves and mechanically generated waves in the presence of wind will be carried out in clean water and water mixed with various concentrations of several soluble surfactants, and limited experiments in salt water. Cinematic Laser Induced Fluorescence (LIF) measurements of the streamwise and cross stream breaking wave pro le histories, shadowgraph movies of droplet ejections, subsequent motions and size distributions, and Particle Image Velocimetry (PIV) measurements of the 'flow field in the wave crest will be performed from an instrument carriage which will be set to move along the tank with the breaking wave crests or other significant features of the wave system. Measurements of the vertical distribution of droplets and droplet fluxes will also be carried out at fixed locations in the wave tank. Water surface proper-ties including surface pressure isotherms and surface viscoelastic properties will be measured using a Langmuir trough/longitudinal wave propagation device set up in a small tank and using water samples taken from the wave tank. Also, the maximum bubble pressure method will be used in the wave tank in order to determine the in-situ diffusion constants and surface tension. Finally, Second Harmonic Generation (SHG) measurements of instantaneous free surface surfactant concentration will be performed at a fixed location in the tank. All of the above measurements will be used to explore the physics of the droplet ejection, motion and evaporation process.Broader Impacts: Since droplet production by breaking waves makes an important contribution to air-sea transfer processes, the proposed research will contribute to our understanding of the climate including important phenomena such as global climate change. The results of this study will be applicable to understanding engineering flows (such as flow around ships or in chemical processing) in which free surface and spray generation are involved. The study will contribute to the education of students in the sciences by supporting one graduate student, one undergraduate student and a part-time post doctoral researcher. The PI will also give approximately one talk or host one field visit to his laboratory each semester for local area high school students in order to introduce them to the subject area of this research. It is hoped that this may foster interest in pursuing oceanography in their university studies.