Experiments on fluids and grains

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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.