Low-frequency oscillations and convective phenomena in a density-inverted vibrofluidized granular system.

Low-frequency oscillations (LFOs) are thought to play an important role in the transition between the Leidenfrost and convective states of a vibrated granular bed. This work details the experimental observation of LFOs, which are found to be consistently present for a range of driving frequencies and amplitudes, with particles of varying material and using containers of differing material properties. The experimentally acquired results show a close qualitative and quantitative agreement with both theory and simulations across the range of parameters tested. Strong agreement between experimental and simulation results was also observed when investigating the influence of sidewall dissipation on LFOs and vertical density profiles. This paper additionally provides evidence of two phenomena present in the Leidenfrost state: a circulatory motion over extended time periods in near-crystalline configurations, and a Leidenfrost-like state in which the dense upper region displays an unusual inverse thermal convection.