ABSTRACT

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.

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