Inertial jets from cavity collapse & granular impact

理论/模拟研究的重点是液体和颗粒射流，在自由表面的影响。对于液体流动，研究将检查在空腔塌陷时形成的射流。这项工作将集中在一般的情况下，动力学不是轴对称的，而是完全三维的。对于颗粒流，研究将集中在一个密集的颗粒射流与固体目标碰撞时形成的喷出物片。智力优点：在这两个问题中，许多小规模的偏差是目前在初始状态引起喷射。最近的研究表明，在从坍缩空腔中喷射时，首先形成射流的界面形状一般是完全三维的，其特征在于强烈的方位扭曲。在颗粒碰撞中，射流中的每个非粘性颗粒与目标碰撞，并对平均运动引入小扰动。直觉上，人们会认为这些偏差会阻止喷射并产生无序的响应。强烈扭曲的空腔应该破裂成一簇气泡，而不是形成一个强大的中心射流。颗粒射流在与目标碰撞时，应该破碎成扩散喷雾，而不是形成具有明确喷射角的薄喷射物片。这两种情况下的反直觉结果将它们与流体动力学的核心难题联系起来。在某些情况下，强强迫似乎以组织动力学的方式起作用，在无序的背景中产生连贯的结构（中央喷流或薄的喷出物片）。对这两个特殊例子的研究见解是新颖的，概念上简单，实验上可以实现，可能会改变我们对广泛现象的理解。更广泛的影响：溃坝射流被认为会导致潜艇涡轮机的腐蚀、蒸汽涡轮机的故障以及海岸断裂处的波浪破坏。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。目前正在开发依靠湍流诱导射流精确切割气泡的微流体装置。雪崩，或罗克瀑布，以高速传播，可以最终喷出大量的材料向上时，他们遇到的障碍。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，许多药物和食品被加工成颗粒流。拟议的研究还为研究生提供了良好的教育。它结合了理论和实验之间的密切合作。作为芝加哥大学的一部分，本科生将被招募从事该项目的实验和模拟方面的工作。本科生的研究经验（REU）计划。研究结果也将纳入PI开发的两门选修课程（一门本科生/一门研究生）的课程。

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.