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

智力优势：在风波系统中，水滴的产生及其随后的运动和蒸发是空气-水界面中质量、热量和动量传递过程的重要组成部分。在波浪槽和野外测量了这些液滴的分布和大小。众所周知，海洋表面被表面活性剂单层覆盖，表面活性剂对包括水滴喷射在内的许多自由表面现象都有重要影响。本实验的目的是探索破波形成液滴的机制，以及这些液滴随后在有和没有表面活性剂的情况下的运动和蒸发。机械造波、风波和有风条件下机械造波的实验将在清洁水中和混合了不同浓度的几种可溶性表面活性剂的水中进行，在盐水中进行有限的实验。电影激光诱导荧光（LIF）测量流向和横流破碎波的历史，水滴喷射的阴影影像，随后的运动和大小分布，以及波峰处流场的粒子图像测速（PIV）测量将在仪器车上进行，该仪器将被设置为沿着破碎波波峰或波浪系统的其他重要特征移动的坦克。液滴垂直分布和液滴通量的测量也将在波浪槽的固定位置进行。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Langmuir槽/纵波传播装置和从波浪水箱中采集的水样进行测量。此外，波浪槽将采用最大气泡压力法来确定原位扩散常数和表面张力。最后，二次谐波生成（SHG）测量瞬时自由表面活性剂浓度将在槽内的固定位置进行。所有上述测量将用于探索液滴喷射、运动和蒸发过程的物理特性。更广泛的影响：由于波浪破碎产生的液滴对海气转移过程做出了重要贡献，因此拟议的研究将有助于我们对气候的理解，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工程流动（如船舶周围的流动或化学加工），其中涉及自由表面和喷雾的产生。该研究将通过资助一名研究生、一名本科生和一名兼职博士后研究人员，为学生的科学教育做出贡献。PI每学期还将为当地高中学生提供大约一次讲座或组织一次实地考察，以便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.