Experiments on fluids and grains

非技术摘要这个项目关注的是流体中一组远离平衡的现象，这些现象似乎违背了我们的直觉。有六个具体的目标：(I)了解液滴在击中干燥的固体衬底时如何飞溅的机制。结果发现，去除环境空气可以完全抑制液滴的飞溅能力；(Ii)研究粘性指进不稳定性是如何在去除稳定力即表面张力时改变其基本性质的，粘性指进不稳定性是由于较低粘性的流体在两个平板之间的细缝中取代较粘性的流体而发生的。研究发现，它不仅不会变得更加不稳定，反而可以完全停止指进；(Iii)了解液滴在外部流体中合并时如何合并。研究发现，外部流体的粘度通常在动力学中起着微不足道的作用；(Iv)测量莱登弗罗斯特液滴的动力学。这样的水滴漂浮在它们自己的蒸汽层上；(V)研究两个粒子簇之间的碰撞中能量是如何消散的。当干扰锋横扫星系团时，能量会迅速损失；(Vi)研究一种新形式的记忆，这种记忆存储在流体达到最终稳定状态之前的瞬时行为中。这种记忆最初会记住所有的输入，但随后会失去记住它们的能力，即使它们不断地应用。更广泛影响的三个不同方面将被解决：(I)所述现象对技术过程具有重要影响；(Ii)从高中生到博士后，让年轻科学家参与研究仍将是一个高度优先事项；(Iii)将把对尖端科学的兴趣带给普通公众，包括与博物馆合作，将继续进行。技术摘要本项目旨在研究处于远离平衡状态的流体。第一个主题是了解去除环境空气可以完全抑制水滴飞溅能力的机制。第二个主题是研究Hele-Shaw几何中的粘性指进不稳定性如何在去掉稳定力(表面张力)后变得更加稳定。第三个项目将是了解液滴在外部流体中融合时如何聚合。在第四个实验中，将研究莱登弗罗斯特液滴的动力学。第五个实验研究了两个粒子群之间的碰撞中能量是如何消散的。最后，将研究一种新的记忆形式，这种记忆可以存储在流体达到最终稳定状态之前的瞬时行为中。将解决更广泛影响的三个不同方面：(I)应用：所述现象对技术过程具有重要影响；(Ii)教育和培训：将年轻科学家，从高中生到博士后，带入研究仍将是一个高度优先事项；(Iii)拓展：将把对尖端科学的兴趣带给普通公众，包括与博物馆合作。

Non-Technical AbstractThis project focuses on a set of far-from-equilibrium phenomena in fluids that seemingly defy our intuition. There are six specific goals: (i) to understand the mechanism of how a liquid drop splashes when it hits a dry solid substrate. It was found that the removal of the ambient air can completely suppress a drop's ability to splash; (ii) to study how the viscous-fingering instability, which occurs as a less viscous fluid displaces a more viscous one in a thin gap between two flat plates, changes its fundamental nature when the stabilizing force, the surface tension, is removed. It was found that, instead of becoming more unstable, it can stop fingering completely; (iii) to understand how fluid drops coalesce when they merge inside an outer fluid. It was found that the viscosity of the outer fluid often plays an insignificant role in the dynamics; (iv) to measure the dynamics of a Leidenfrost drop. Such drops float on a layer of their own vapor; (v) to study how energy is dissipated in the collision between two clusters of particles. The energy is rapidly lost as jamming fronts sweep across the clusters; (vi) to investigate a new form of memory that is stored in the transient behavior of a fluid before it reaches its final steady state. Such memories initially remember all inputs but then lose the ability to remember them even as they are continually applied.There are three distinct aspects of broader impacts that will be addressed: (i) The phenomena addressed have important implications for technological processes; (ii) Bringing young scientists, from high-school students to postdocs, into research will remain a high priority; (iii) Bringing the fascination with cutting-edge science to the general public, including working with museums, will continue to be pursued.Technical AbstractThis project seeks to investigate fluids that are in states far-from-equilibrium. The first topic is to understand the mechanism whereby removing the ambient air can completely suppress a drop's ability to splash. A second topic is to study how the viscous-fingering instability in the Hele-Shaw geometry becomes more stable when the stabilizing force, the surface tension, is removed. A third project will be to understand how fluid drops coalesce when they merge inside an outer fluid. In a fourth experiment, the dynamics of a Leidenfrost drop will be investigated. A fifth experiment studies how energy is dissipated in the collision between two clusters of particles. Finally, a new form of memory that can be stored in the transient behavior of a fluid before it reaches its final steady state will be studied.There are three distinct aspects of broader impacts that will be addressed: (i) Applications: the phenomena addressed have important implications for technological processes; (ii) Education and Training: bringing young scientists, from high-school students to postdocs, into research will remain a high priority; (iii) Outreach: bringing the fascination with cutting-edge science to the general public, including working with museums, will continue to be pursued.