Gas-driven subharmonic waves in a vibrated two-phase granular material
Department of Physics & Center for Nonlinear and Complex Systems, Duke University, 27708-0305, Durham, NC, USA
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Accepted: 7 March 2008
Published online: 18 April 2008
Vibrated powders exhibit striking phenomena: subharmonic waves, oscillons, convection, heaping, and even bubbling. We demonstrate novel rectangular profile subharmonic waves for vibrated granular material, that occur uniquely in the two-phase case of grains, and a fluid, such as air. These waves differ substantially from those for the gas-free case, exhibit different dispersion relations, and occur for specific shaking parameters and air pressure, understandable with gas-particle flow models. These waves occur when the gas diffusively penetrates the granular layer in a time comparable to the shaker period. As the pressure is lowered towards P =0, the granular-gas system exhibits a Knudsen regime. This instability provides an opportunity to quantitatively test models of two-phase flow.
PACS: 45.70.-n Granular systems – / 47.20.-k Flow instabilities –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2008