(77f) Rayleigh-Taylor Instability in Vibrated Gas-Fluidized Particles

A Rayleigh-Taylor-like instability^1,2 forms in a binary set of particles of different density subject to upward gas flow and vertical vibration³. “Fingers” and “bubbles” of light particles rise through heavy particles despite a lack of effective surface tension between the two types of particles. CFD-DEM simulations show that gas flow channels through fingers of lighter, larger particles due to a higher permeability of these particles to gas flow, locally increasing drag and causing these fingers to grow³. We demonstrate that the same physical mechanism causes an isolated “bubble” of light grains to rise and an isolated “droplet” of heavy grains to break up forming a binary branching pattern³. We explore how the combination of vibration and gas flow causes a bubble-free fluidization state in Geldart Group B and D particles and how this state can lead to other structured flow patterns.

References

(1) Rayleigh, J. W. S. B. Scientific Papers: 1881-1887; University Press, 1900.

(2) Taylor, G. I. The Instability of Liquid Surfaces When Accelerated in a Direction Perpendicular to Their Planes. I. Proc. R. Soc. Lond. A 1950, 201 (1065), 192–196.

(3) McLaren, C.; Kovar, T. M.; Penn, A.; Müller, C. R.; Boyce, C. M. Gravitational Instabilities in Binary Granular Materials. Proceedings of the National Academy of Sciences 2019, Accepted.