oscillating gas-fluidized granular system
Jie Li, Igor S. Aronson 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.