Abstract
When grains flow out of a silo, flow rate increases with exit size . If is too small, an arch may form and the flow may be blocked at the exit. To recover from clogging, the arch has to be destroyed. Here we construct a two-dimensional silo with movable exit and study the effects of exit oscillation (with amplitude and frequency ) on flow rate, clogging, and unclogging of grains through the exit. We find that, if exit oscillates, remains finite even when (measured in unit of grain diameter) is only slightly larger than one. Surprisingly, while increases with oscillation strength as expected at small , decreases with when due to induced random motion of the grains at the exit. When is small and oscillation speed is slow, temporary clogging events cause the grains to flow intermittently. In this regime, depends only on —a feature consistent to a simple arch breaking mechanism, and the phase boundary of intermittent flow in the plane is consistent to either a power law: or an exponential form: . Furthermore, the flow time statistic is Poissonian whereas the recovery time statistic follows a power-law distribution.
- Received 26 May 2017
DOI:https://doi.org/10.1103/PhysRevE.96.032906
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