Flow and clog in a silo with oscillating exit.

Area of Science:

• Physics of granular materials
• Fluid dynamics of granular flow

Background:

• Grain flow from silos can be blocked by arching at the exit.
• Arch formation necessitates active intervention for flow recovery.

Purpose of the Study:

• Investigate the impact of movable exit oscillation on grain flow rate and clogging.
• Analyze the effects of oscillation amplitude (A) and frequency (f) on silo discharge.

Main Methods:

• Utilized a two-dimensional silo model with a movable oscillating exit.
• Systematically varied exit size (D), oscillation amplitude (A), and frequency (f).
• Measured flow rate (W), clogging, and unclogging dynamics.

Main Results:

• Oscillation maintains finite flow rate (W) even for exit sizes (D) near one grain diameter.
• Flow rate initially increases with oscillation strength (Γ) at small D but decreases at D≥5.
• Intermittent flow occurs at low oscillation speeds (v), with W depending solely on v.
• Phase boundary for intermittent flow follows D∝v^{-7} or D∝e^{-D/0.55}.
• Flow time statistics are Poissonian; recovery time statistics follow a power law.

Conclusions:

• Exit oscillation is an effective strategy to prevent and recover from grain flow blockages in silos.
• The relationship between flow rate and oscillation strength is complex and depends on exit size.
• The dynamics of intermittent flow and clogging recovery exhibit distinct statistical behaviors.