Inertial jets from cavity collapse & granular impact

理论/模拟研究的重点是在自由表面上撞击的液体和颗粒射流。对于液体流动，研究将检查空腔崩塌时形成的射流。这项工作将集中在动力学不是轴对称而是完全三维的一般情况下。对于颗粒流，研究将集中在密集堆积的颗粒射流与固体目标碰撞时形成的喷射层。智力优势：在这两个问题中，在初始状态中存在许多小规模偏差，从而导致喷射。最近的研究表明，从塌缩空腔喷射时，首先形成射流的界面形状一般是完全三维的，其特征是强烈的方位扭曲。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产生小的扰动。直觉上，人们会期望这些偏差会阻止喷射并产生混乱的反应。强烈扭曲的空腔应该分裂成一簇气泡，而不是形成一个强大的中央射流。颗粒射流在与目标发生碰撞时，应破碎成弥漫性喷雾，而不是形成具有明确喷射角度的薄喷射片。这两种情况的反直觉结果都将它们与流体动力学中的一个核心难题联系起来。在某些情况下，强作用力似乎以这样一种方式组织了动力学，从无序的背景中产生了一个连贯的结构（一个中央喷流或一个薄的喷射层）。从对这两个特殊例子的研究中获得的见解是新颖的，概念上简单的，并且可以通过实验获得，这可能会改变我们对广泛现象的理解。更广泛的影响：坍缩引起的射流被认为会导致潜艇涡轮机的侵蚀，蒸汽涡轮机的故障以及海浪对海岸的破坏。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。依靠坍缩诱导射流精确切割气泡的微流体装置正在开发中。雪崩或岩石坠落以高速传播，当它们遇到障碍物时，最终会向上喷射出大量物质。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，许多药品和食品都是以粒子流的形式加工的。拟议的研究也为研究生提供了良好的教育。它结合了理论和实验的紧密合作。作为芝加哥大学的一部分，本科生将被招募来从事该项目的实验和模拟方面的工作。美国本科生研究经验（REU）项目。研究的结果也将纳入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.