Collaborative Research: Experimental and numerical studies of the effects of wind, wave scale, and salinity on bubble entrainment by breaking waves

通过比例尺模型实验室实验和计算流体力学(CFD)模拟，研究了波浪尺度、波浪斜率、风强迫和盐度对破碎海浪中气泡的产生和扩散的作用。这项工作的动机是气泡在与气候有关的海-气交换中所发挥的关键作用，包括二氧化碳转移、气溶胶产生和海洋反照率。识别控制白帽中气泡夹带的物理过程及其对波浪尺度、波浪斜率、风强迫和盐度的依赖将从根本上改变我们模拟海-气相互作用的能力。目前，白帽中的气泡只有三组海洋数据，这显然不足以确定气泡夹带和环境强迫之间的任何基本物理联系。CFD模拟已经成为研究波浪破碎的有力工具，但可实现的长度尺度仍然比海洋白浪小几个数量级，而且重要的物理效应，包括盐度对气泡合并的影响，风的作用，以及波浪尺度的影响，还没有得到充分的探讨。用真实的海洋模型验证CFD对海浪破碎的模拟将有助于将其用于研究海洋尺度的交换过程，同时确定应在哪里做出最大努力来将数值模式缩放到相关的海洋过程。此外，来自实验的数据将有助于改进现有的气泡介导的海-气交换过程模型。还包括其他活动，以扩大该项目的影响。参与的实验室坚定地致力于支持社会各阶层不同学术水平的研究和教育的整合。SIO PIs将与斯克里普斯白桦水族馆(BAS)的教育专业人员合作，增加对STEM的参与，并扩大对STEM职业的参与。BAS的工作人员和加州大学圣地亚哥分校的Create STEM Success Initiative将利用斯克里普斯海洋大气研究模拟器(SOARS)的资源共同设计、评估和实施体验式学习计划。为了解决STEM学生在获得STEM学习机会方面的不平等以及BIPOC学生在地球科学中的代表性不足问题，“探索海洋STEM职业”计划将吸引来自历史上被边缘化群体的初中生和高中生，并与合作伙伴合作，通过包括学术咨询和大学申请支持在内的服务，提高学生的兴趣和兴奋。此外，还包括资助两名暑期本科生继续深造海洋科学的经费。PiS Deane和Stokes将参加BAS外联工具：海洋科学透视系列讲座。皮申将领导开发一个用于气候和环境应用的水波计算机模拟门户网站，作为向部落学院和大学、社区学院和少数民族服务机构的学生展示地球科学的教材。该门户将通过地球科学联盟传播，这是一个旨在扩大美洲原住民参与地球科学的全国性联盟。来自三个规模越来越大、环境越来越复杂的波道的实验数据将与最先进的CFD计算进行比较，以研究气泡夹带的流体动力学及其对环境参数的依赖。这些实验将利用最近委托使用的斯克里普斯海洋-大气研究模拟器，该模拟器为风力驱动的海面提供了一个现实但可控的代理。CFD模拟将利用最新的算法进展，包括使用具有一致质量和动量平流方案的耦合水平集和流体体积方法的高保真气液界面捕获算法，最优网络气泡识别和跟踪算法，以及自适应网格细化，以提供对破碎波峰内的空气卷吸过程和气泡行为的新见解。实验和模拟的协调将能够验证CFD模型，进一步的算法和建模进步的动机，以及对风驱动的海-气界面上气泡中介的交换过程的洞察。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This is a study of the role of wave scale, wave slope, wind forcing, and salinity on the generation and dispersal of bubbles in breaking ocean waves through scale model laboratory experiments and computational fluid dynamics (CFD) simulations. The work is motivated by the critical role played by bubbles in climate-related air-sea exchanges, including CO2 transfer, aerosol production, and ocean albedo. Identification of the physical processes controlling bubble entrainment in whitecaps and their dependence on wave scale, wave slope, wind forcing, and salinity will fundamentally alter our ability to model air-sea interactions. At present, there are only three oceanic data sets of bubbles in whitecaps, which is obviously insufficient to determine any fundamental physical connection between bubble entrainment and environmental forcing. CFD simulations have become a powerful tool to study wave breaking but achievable length scales are still orders of magnitude smaller than oceanic whitecaps and important physical effects, including salinity effects on bubble coalescence, the role of wind-forcing, and the effects of wave scale, are not fully explored. Validating CFD simulations of wave breaking with a realistic ocean proxy will facilitate their use to study ocean-scale exchange processes while simultaneously identifying where the greatest effort should be directed to scale the numerical models to relevant oceanic processes. Moreover, data from the experiments will help improve existing models of bubble-mediated, air-sea exchange processes. Additional activities are included to broaden the impact of the project. The participating laboratories have a strong commitment to supporting the integration of research and education at various academic levels across a broad spectrum of society. SIO PIs will work with educational professionals at the Birch Aquarium at Scripps (BAS) to increase engagement in STEM and broaden participation in STEM careers. Staff at BAS and the CREATE STEM Success Initiative at UC San Diego will co-design, evaluate, and implement experiential learning programs using the resources of the Scripps Ocean Atmosphere Research Simulator (SOARS). To address inequities in access to STEM learning opportunities and under-representation of BIPOC students in the geosciences, the “Exploring Ocean STEM Careers” program will engage middle and high school students from historically marginalized groups and work with partners to build on students’ interest and excitement with services that include academic counseling and college application support. In addition, funding is included to support two summer undergraduate interns to further their education in marine science. PIs Deane and Stokes will participate in the BAS outreach vehicle: Perspectives on Ocean Science lecture series. PI Shen will lead the development of a portal of computer modeling of water waves for climate and the environment applications as teaching materials to illustrate Geosciences to students at tribal colleges and universities, community colleges, and minority serving institutions. The portal will be disseminated through the Geoscience Alliance, a national alliance for broadening participation of Native Americans in GeosciencesData from experiments in three wave channels of increasing scale and environmental complexity will be compared with state-of-the-art CFD computations to study the fluid dynamics of bubble entrainment and its dependence on environmental parameters. The experiments will leverage the recently commissioned Scripps Ocean-Atmosphere Research Simulator, which provides a realistic yet controllable proxy for the wind-driven sea surface. The CFD simulations will take advantage of recent algorithmic advances, including high-fidelity gas-liquid interface capturing algorithms using the coupled level-set and volume-of-fluid methods with consistent mass and momentum advection schemes, an optimal network bubble identification and tracking algorithm, and adaptive mesh refinement, to provide new insights into air entrainment processes and bubble behavior within breaking wave crests. Reconciliation of the experiments and simulations will enable verification of the CFD models, motivation for further algorithmic and modeling advances, and insights into bubble-mediated exchange processes across the wind-driven air-sea interface.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.