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

智力优势：在风浪系统中，水滴的产生、运动和蒸发是气-水界面质量、热量和动量传递过程的重要组成部分。已在波浪槽和现场测量了这些液滴的分布和尺寸。众所周知，海洋表面被表面活性剂单层覆盖，并且表面活性剂可以对包括水滴喷射在内的许多自由表面现象具有重要影响。拟议的实验室实验的目的是探索通过破碎波和随后的运动和蒸发的这些液滴与和没有表面活性剂的液滴形成的机制。 机械产生的波浪，风浪和机械产生的波浪在风的存在下的实验将在清洁的水和与各种浓度的几种可溶性表面活性剂混合的水中进行，并在盐水中进行有限的实验。电影激光诱导荧光（LIF）测量流向和横向流破碎波剖面历史，液滴喷射的阴影电影，随后的运动和尺寸分布，粒子图像测速（PIV）波峰中的流场的测量将从仪器托架执行，该仪器托架将被设置为沿着具有破碎波峰或其它显著特征的罐沿着移动。波系 还将在波浪槽的固定位置测量液滴和液滴通量的垂直分布。将使用设置在小型水槽中的朗缪尔槽/纵波传播装置和使用从波浪水槽中采集的水样来测量水面特性，包括表面压力等温线和表面粘弹性特性。此外，最大气泡压力法将用于波槽，以确定在现场的扩散常数和表面张力。最后，将在罐中的固定位置进行瞬时自由表面表面活性剂浓度的二次谐波产生（SHG）测量。更广泛的影响：由于碎波产生的水滴对海气传输过程有重要贡献，拟议的研究将有助于我们了解气候，包括全球气候变化等重要现象。这项研究的结果将适用于了解工程流动（如船舶周围的流动或在化学加工），其中涉及自由表面和喷雾的产生。该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，为理科学生的教育做出贡献。PI每学期还将为当地高中学生提供大约一次演讲或主持一次实地考察，以向他们介绍本研究的主题领域。希望这可以培养他们在大学学习海洋学的兴趣。

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.