Intermittency and velocity fluctuations in hopper flows prone to clogging

Area of Science:

• Experimental physics
• Fluid dynamics
• Granular materials science

Background:

• Granular media discharging from hoppers often exhibit a critical outlet size (D_c) above which clogging is presumed to cease.
• Understanding the dynamics of granular flow and clogging is crucial for various industrial processes.

Purpose of the Study:

• To experimentally investigate the dynamics of granular media in a discharging hopper.
• To determine if a critical outlet size (D_c) exists and to analyze flow behavior for D < D_c and D > D_c.
• To characterize velocity distributions and temporal intermittency in granular flow.

Main Methods:

• Experimental study of granular media flow in a discharging hopper.
• Measurement of time-averaged velocity distributions and temporal intermittency.
• Characterization of vertical velocity distributions using standard deviation and skewness.
• Quantification of intermittency using the two-sample Kolmogorov-Smirnov (D_KS) statistic.

Main Results:

• No discontinuity or kink was observed in velocity distribution measures or intermittency as a function of outlet size.
• The findings suggest that a well-defined critical outlet size (D_c) does not exist, and clogging remains a possibility regardless of outlet size.
• The intermittency time scale is dictated by the speed of grains exiting the hopper.

Conclusions:

• The absence of a critical outlet size implies that granular hopper flow clogging is always possible.
• The exit grain speed is a key factor in setting the intermittency time scale.
• Results align with models where clogging arises from independent sampling of stable exit configurations.