Dept. Colloquium: Wendy Zhang, Physics, James Franck Inst., Center for Integrative Science, UofC
Title: Still water: dead zones and collimated ejecta from the impact of granular jets
Abstract: Children learn that liquids are an intermediate state of matter: like gases, they flow easily but, like solids, they exist in a condensed state due to inter-particle attractions. In graduate school they may be taught that liquids can be simulated without attractions if the particle density is kept high by confinement. However, even without attractions or confinement, non-cohesive particles can behave like a liquid: when a high-density jet of
grains hits a target it ejects particles in a thin sheet similar to the water bells created by liquid-jet impact3. Our experiments, simulations and continuum modeling show that such ejecta sheets are generic and independent of the jet's internal kinematic features and the target shape. We show that this insensitivity arises because, surprisingly, the highly dissipative dense granular jet impact is controlled by the limit of
perfect fluid flow. In contrast with the expectation that scattering provides sufficient information to reconstruct the internal state, the macroscopic observables, e.g., thin-sheet ejection angle, give little information about the jet dynamics when the density is high.