Bifurcations
of periodic and disordered patterns in
oscillating
gas-fluidized granular system
Jie Li, Igor
S. Aranson and Wai Kowk
Argonne National Lab.
We report our experimental study of thin granular layer
fluidized by periodically-modulated gas flow. We observed a sequence of
well-defined transition between disordered states dominated by spontaneous
bubbling-fluidization to ordered periodic sub-harmonic patterns as the
frequency, the amplitude of modulation and the flow rate varied. Ordered states
include periodic square, stripes and quasi-hexagon. More complicated
“flower-like” structure was also observed. As driven frequency increases, we
observed a hysteria phenomenon. Then after, the interaction between driving
flow and bed layer gives a way to the interaction between diving flow and
bubbles. The wavelength of observed patterns is determined by the frequency of
the modulation and mean flow rate. The transition to periodic patterns is associated
with noticeable decrease of pressure drop across the granular layer.
Interestingly, the patterned structures are found to be
closely related to the bed natural frequency and bubble frequency: - it is the driving
oscillatory flow that triggers the resonances of these natural frequencies. As a sequence, it converts the original random
flows to regular flows.