ISS: Gravitational Effects on the Faraday Instability

当两种不混溶的液体受到垂直于其界面的振荡力学场作用时，就会产生不稳定性。这种不稳定性表现为在界面处突然产生波和流体运动，称为法拉第不稳定性。研究了重力对液体双分子层界面处振动诱导不稳定性的影响。在国际空间站上进行的实验将测试法拉第不稳定性的起源及其相关的流动模式的理论。本研究将首次尝试利用独特的微重力环境来获取法拉第不稳定性问题的信息。解决这个问题可能会影响地球上的重要过程，包括生物分离中的微流体混合、微尺度传热、增材制造、雾化燃料喷射和图案基板开发。该项目涉及研究生和本科生与空间实施伙伴工程师一起工作。该项目还包括来自农村学校的高中和初中学生，通过暑期科学课程、课堂演示、动手实验和微重力实验的现场展示。法拉第不稳定性的产生是由于施加的振动频率与具有界面的液体系统的固有频率之间的共振。界面形态以重力为主，对界面张力不敏感。我们假设，在没有重力的情况下，不稳定性的长度尺度比地球重力下小得多，从而产生了界面张力的主导作用。反过来，这应该会导致界面在没有重力的情况下在小频率下破裂，而不是在高频率下。本研究项目旨在验证法拉第不稳定性模型，定义在国际空间站上进行的没有重力的实验，并将这些实验与地面实验进行比较。该项目还试图确定界面何时饱和到驻波，以及何时发生灾难性破裂。实验涉及频率和幅度控制下的直接成像，而理论涉及采用高保真谱方法的Floquet和非线性分析。在控制良好、独特的微重力环境下，通过收集无可辩驳的证据来验证模型，有可能转化为其他重要领域，如声学、静电、磁悬浮和流体界面的作用力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

When two immiscible liquids are subject to an oscillating mechanical field that is applied perpendicular to their interface an instability may arise. This instability is manifested by the sudden generation of waves and fluid motion at the interface and is termed the Faraday instability. The effect of gravity on vibration-induced instability at the interface between liquid bilayers will be investigated. Experiments performed on the International Space Station will test theories about the onset of the Faraday instability and its associated flow patterns. This study will be the first attempt to utilize the unique environment of microgravity to obtain information on the Faraday instability problem. Addressing this question could impact important processes here on Earth, including microfluidic mixing in bio-separations, microscale heat transfer, additive manufacturing, atomization-fuel injection, and patterned substrate development. The project involves graduate and undergraduate students working with space-implementation partner engineers. The project also involves both high school and middle school students from rural schools through summer science programs, in-class demonstrations, hands-on experiments, and live displays of microgravity experiments.The Faraday instability arises from resonance between the applied frequency of shaking and the natural frequency of a liquid system with an interface. The morphological patterns of the interface are dominated by gravity and insensitive to interfacial tension. It is hypothesized that, when gravity is absent, the length scales of the instability are much smaller than under Earth’s gravity bringing out the dominant effect of interfacial tension. This, in turn, ought to cause the interface to rupture in the absence of gravity for small frequencies, but not for high frequencies. This research project seeks to validate models for Faraday instability with defining experiments conducted in the absence of gravity on the International Space Station, comparing these to ground experiments. The project also seeks to determine when the interface saturates to standing waves and when it breaks catastrophically to rupture. Experiments involve direct imaging under frequency and amplitude control while the theory involves Floquet and nonlinear analyses that employ high fidelity spectral methods. Validation of models by irrefutable evidence gathered under a well-controlled, unique microgravity environment have the potential to be translatable to other important fields such as acoustic, electrostatic, and magnetic levitation and forcing of fluid interfaces.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.