Inertial jets from cavity collapse & granular impact

理论/模拟研究的重点是冲击自由表面的液体和颗粒射流。对于液体流动，这项研究将检查空穴坍塌时形成的射流。这项工作将集中在一般情况下，动力学不是轴对称的，而是完全三维的。对于颗粒流，研究将集中在密集填充的颗粒射流与固体靶碰撞时形成的喷射层。智力优势：在这两个问题中，在初始状态下都存在许多小范围的偏差，从而导致喷射。在从塌陷的空腔中喷射时，最近的研究表明，最初形成喷流的界面形状通常是完全三维的，具有强烈的方位扭曲特征。在颗粒碰撞中，射流中的每个非粘性颗粒与目标碰撞，并对平均运动产生微小的扰动。直觉上，人们会认为这些偏差将阻止喷射，并造成无序的反应。强烈扭曲的空腔应该破裂成气泡阵雨，而不是形成强大的中心喷流。颗粒射流在与靶体碰撞时，应分解为扩散喷雾，而不是形成具有明确喷射角的薄层喷射片。这两个案例中与直觉相反的结果将它们与流体动力学中的一个中心谜题联系在一起。在某些情况下，强烈的强迫似乎以这样一种方式来组织动力学，从无序的背景中产生连贯的结构(中心喷流或薄薄的喷射物)。对这两个特殊例子的研究洞察到，这两个例子新颖、概念简单，而且可以通过实验获得，这可能会改变我们对广泛类别现象的理解。更广泛的影响：坍塌引发的喷气式飞机被认为会导致潜艇涡轮机的磨损，蒸汽涡轮机的故障，以及岸边断裂的海浪破坏。喷雾和雾化技术依赖于形成薄的、快速移动的射流，这些射流分解成许多液滴。人们正在开发一种微流控装置，这种装置依靠坍塌诱导的喷射来精确地裂解气泡。当遇到障碍物时，高速传播的雪崩或岩石坠落可能会最终将大量物质向上抛出。在较慢的尺度上，暴雨中雨滴撞击形成的陨石坑可能是土壤侵蚀的重要机制。最后，许多药品和食品被加工成颗粒流。所提出的研究也为研究生提供了良好的教育。它将理论与实验紧密结合在一起。作为芝加哥大学S本科生研究经验项目的一部分，本科生将被招募从事该项目的实验和模拟方面的工作。这项研究的结果也将被纳入该协会开发的两门选修课(一门本科/一门研究生)的课程中。

The theoretical/simulational research focuses on liquid and granular jets that impact at a free surface. For liquid flow, the research will examine the jet formed upon collapse of a cavity. The work will focus on the generic situation where the dynamics is not axisymmetric but instead fully three-dimensional. For granular flow, the research will focus on the ejecta sheet formed when a densely packed granular jet collides with a solid target. Intellectual Merit: In both problems, numerous small-scale deviations are present in the initial state giving rise to jetting. In jetting from a collapsing cavity, recent studies revealed that the shape of the interface which first forms into a jet is generically fully three-dimensional, characterized by strong azimuthal distortions. In granular impact, each non-cohesive grain in the jet collides with the target and introduces a small disturbance to the mean motion. Intuitively one would expect that these deviations would prevent jetting and create a disordered response. The strongly distorted cavity should break up into a shower of air bubbles instead of forming a strong central jet. The granular jet, upon colliding with the target, should break up into a diffuse spray instead of forming a thin ejecta sheet with a well-defined ejection angle. The counter-intuitive outcomes in both cases connect them to a central puzzle in fluid dynamics. Under some circumstances, strong forcing appears to act in such a way as to organize the dynamics, producing a coherent structure (a central jet or a thin ejecta sheet) out of a disordered background. Insights from research into these two particular examples, which are novel, conceptually simple, and experimentally accessible can potentially transform our understanding of wide class of phenomena. Broader Impacts: Collapse-induced jets are believed to cause erosion of turbines in submarines, failure in steam turbines as well as wave-damage on shore breaks. Spray and atomization technologies rely on the formation of thin, fast moving jets that break-up into many droplets. Microfluidic devices that rely on collapse-induced jets to cleave bubbles with precision are being developed. Snow avalanches, or rock falls, propagating at high speeds can end up ejecting a great deal of materials upwards when they encounter an obstacle. On a slower scale, the craters formed by raindrop impact in a heavy downpour can be an important mechanism for soil erosion. Finally, many drugs and food products are processed as streams of particles. The proposed research also provides an excellent education for graduate students. It combines close collaboration between theory and experiment. Undergraduates will be recruited to work on both the experimental and simulation aspects of the project as part of the University of Chicago?s Research Experience for Undergraduates (REU) program. Results from the research will also be incorporated into the curriculum of two elective courses (one undergraduate / one graduate) that the PI has developed.