CAREER: Bubble fragmentation in turbulent flows

在许多环境和工业环境中，湍流中气泡的破裂是很重要的。这些措施包括缓解石油泄漏、船舶和潜艇的船头波中夹带的空气，以及与破碎波相关的海洋-大气相互作用。在湍流的作用下，气泡界面会发生剧烈的变形和破裂，新形成的界面极大地增加了气液两相之间的热量和质量传递。该奖项介绍了一系列关于湍流中气泡破碎的最先进的数值和实验研究。我们的目标是建立一个通用的模型，描述湍流的作用和界面性质对气泡破裂的影响。这将是向前迈出的重要一步，也是设计工程解决方案以及海洋和气候模型的宝贵工具。该奖项还将支持小学生、本科生和研究生的教育活动。通过这项工作开发的软件将是开源的，并将广泛提供给公众和其他对多相流建模感兴趣的研究人员。这项工作将从湍流和界面的物理化学复杂性方面加深对现实条件下气泡破裂现象的多尺度性质的理解。远离临界破裂尺寸的气泡的破裂表现出戏剧性的行为，形成了多个微小的卫星气泡。气泡界面表面活性剂广泛存在于自然界和工业中，它降低了界面张力，影响了气泡的破碎过程。然而，后一方面在很大程度上仍未得到探索。系统的实验和各种湍流构型的直接数值模拟将探索这些多尺度区域。研究人员还将通过控制表面活性剂和盐度条件来实验表征界面的物理化学性质的作用。在没有表面活性剂的情况下，研究人员将确定气泡大小和湍流泰勒微尺度之间的比率(控制激发范围尺度)和气泡大小与临界Hinze尺度之间的比率(控制破裂模式和儿童气泡大小产生的局部或非局部范围)如何控制破裂动力学和子泡统计数据。在表面活性剂存在的情况下，研究人员将表征由于界面的延长稳定性而产生的丝状结构，从而产生更小的气泡碎片。从这些广泛的数据集，将开发一个数学框架，可以实施在多相模拟的纳威-斯托克斯方程。这将允许对具有复杂表面流变性的湍流中的碎裂进行建模。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。

Bubble break up in turbulent flows is important in many environmental and industrial situations. These include oil spill mitigation, air entrained in bow waves in ships and submarines, and ocean-atmosphere interactions associated with breaking waves. The bubble interface may deform and break violently under the action of turbulent flows, and the newly formed interfaces dramatically increase transfer of heat and mass between the gas and liquid phases. This award describes a series of state-of-the-art numerical and experimental studies of the fragmentation of bubbles in turbulent flow. The goal is to produce a general model that describes the roles of turbulent flow and the interface properties on the rupture of bubbles. This will result in a major step forward and a valuable tool in designing engineering solutions and ocean and climate modeling. The award will also support educational activities for elementary school students, undergraduates, and graduate students. Software developed through this work will be open source and widely available to the public and other researchers interested in modeling multiphase flows.This work will develop an understanding of the multi-scale nature of bubble break-up phenomena under realistic conditions in terms of turbulent flow and the physico-chemical complexity of the interfaces. The break-up of bubbles far from the critical break-up size exhibits dramatic behavior, with the formation of multiple tiny satellite bubbles. The presence of surfactants at the bubble interface, ubiquitous in nature and industry, lowers the interfacial tension and affects the break-up processes. However, this latter aspect remains largely unexplored. Systematic experiments and direct numerical simulations for various turbulence configurations will probe these multi-scale regimes. The researchers will also characterize experimentally the role of the physico-chemical properties of the interface by working with controlled surfactant and salinity conditions. In the absence of surfactant, researchers will determine how the break-up dynamics and child bubble statistics are controlled by the ratio between the bubble size and the turbulent Taylor microscale, which controls the excitation range scale, and the ratio between the bubble size and the critical Hinze scale, which controls the break-up mode and the local or non-local range of child bubble size production. In the presence of surfactants, researchers will characterize the filamentary structures that arise due to the extended stability of interfaces, leading to the generation of much smaller bubble fragments. From these extensive data sets, a mathematical framework that can be implemented in multi-phase simulations of the Navier-Stokes equations will be developed. This will allow the modeling of fragmentation in turbulent flow with complex surface rheology.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.