A Parametric Study of the Link between Energy Dissipation and Bubble Creation in Laboratory Breaking Waves

本研究的目的是研究实验室破碎波中能量耗散和气泡产生之间的联系。破碎波的能量耗散是许多重要的上层海洋过程的关键，包括动量转移和气泡介导的气泡-海洋气体运输。这项研究建立在美国国家科学基金会早先的一项拨款结果的基础上，以确定破浪波峰内的泡沫产生机制。早些时候的研究确认了俯冲式破碎器内气泡产生过程的尺度依赖性：大于由湍流压力波动的破碎力和表面张力的稳定力(Hinze标度)之比确定的长度尺度的气泡会受到一系列破碎事件的影响。小于Hinze标度的气泡稳定，不受湍流碎裂的影响。这项研究要解决的两个主要问题是：1)破碎波峰中的湍流能量耗散如何随波能和波斜率的变化而变化；2)Hinze尺度是否如预测的那样随固有的波能耗散而变化？研究计划包括测量不同能量和斜率的破碎波峰内的能量耗散，并估计作为能量耗散函数的湍流气泡破碎的Hinze标度。能量耗散的估计将通过研究玻璃壁水槽中的破碎波包来获得，该波包的能量和斜率范围通过改变波包的光谱组成而变化。断峰区内的能量耗散率将通过两种方法独立估计：生物发光甲藻发光的定量分析和能量守恒。使用生物发光来量化湍流是一项新技术，但已被证明对瞬变的两相流有效。使用光学技术和电导池将获得破碎过程中空气的气泡尺寸分布和空泡率。气泡Hinze标度对应于气泡尺寸分布的斜率的明显变化，这可以从光学测量中估计出来。破碎过程中损失的总能量将通过破碎上下游测量的波包形状的变化来估计，破碎结束时相干和湍流流体运动的剩余能量将通过声学多普勒测速仪和多个事件的集合平均来测量。更广泛的影响。该项目将加强对大气动量向海洋的输送、控制气体输送的小尺度物理过程以及海洋边界层和沿海地区的湍流和气泡产生的了解。所有这些过程都对大气-海洋耦合动力学、全球气候模拟和沿海海洋学产生了广泛的影响。实验和数据分析将包括加州大学圣迭戈分校的一名研究生和本科生实习生参加，以及SIO暑期研究奖学金计划。这些项目资助来自全国各地的学生获得海洋学方面的实践经验。与加州海洋科学教育卓越中心合作，研究小组还与海洋研究所(Sea Bubble！)共同制定了一项外展计划。从而增加公众对海洋-大气相互作用的了解。

ABSTRACTOCE-0450974The objective of this research is to study the link between energy dissipation and bubble creation in laboratory breaking waves. Energy dissipation by breaking waves is key to a number of important upper-ocean processes, including momentum transfer and bubble-mediated air-sea gas transport. This study builds on the results of an earlier NSF grant to identify bubble creation mechanisms within breaking wave crests. The earlier study identified the scale dependence of bubble creation processes within plunging breakers: bubbles larger than a length scale determined by the ratio of the fragmenting forces of turbulent pressure fluctuations and the stabilizing force of surface tension (the Hinze scale) are subject to a cascade of fragmentation events. Bubbles smaller than the Hinze scale are stabilized against turbulent fragmentation. The two main questions to be addressed in this study are: 1) how does the turbulent energy dissipated in the breaking wave crest vary with variations in wave energy and wave slope and 2) does the Hinze scale vary with intrinsic wave energy dissipation as predicted? The research plan consists of measuring of energy dissipation within breaking wave crests for various wave energies and slopes, and estimating the Hinze scale for turbulent bubble fragmentation as a function of energy dissipation. Estimates of energy dissipation will be obtained by studying breaking wave packets in a glass-walled flume for a range of wave energies and slopes, varied by changing the spectral composition of the packets. The energy dissipation rate within the breaking crest region will be independently estimated with two methods: quantitative analysis of the light emission from bioluminescent dinoflagellates, and conservation of energy. Using bioluminescence to quantify turbulence is a recent technique, but has proven effective for transitory, two phase flows. The bubble size distribution and void fraction of air during breaking will be obtained using optical techniques and a conductivity cell. The bubble Hinze scale corresponds to a distinctive change in slope of the bubble size distribution, which can be estimated from the optical measurements. The total energy lost during breaking will be estimated from changes in wave packet shape measured upstream and downstream of breaking, and the residual energy in coherent and turbulent fluid motions at the end of breaking will be measured with acoustic Doppler velocimeters and ensemble averaging of multiple events. Broader Impact. The project will enhance the understanding of atmospheric momentum transport to the ocean, the small-scale physical processes controlling gas transport, and turbulence and bubble production in the marine boundary layer and coastal regions. All of these processes have a broad impact on atmosphere-ocean coupling dynamics, global climate modeling and coastal oceanography. The experiment and data analysis will include the participation of a graduate student and undergraduate interns from UCSD and the SIO summer research fellowship program. These programs sponsor students from around the country to gain hands-on experience in oceanography. Working with the California Center for Ocean Science Education Excellence, the research team is also developing an outreach plan with the Ocean Institute (Sea Bubbles!) so as to increase public understanding of ocean-atmospheric interactions.