Force on a sphere suspended in flowing granulate

Jing Wang, Bo Fan, Tivadar Pongó, Tamás Börzsönyi, Raúl Cruz Hidalgo, Ralf Stannarius

Research output: Contribution to journalLetterAcademicpeer-review


We investigate the force of flowing granular material on an obstacle. A sphere suspended in a discharging silo experiences both the weight of the overlaying layers and drag of the surrounding moving grains. In experiments with frictional hard glass beads, the force on the obstacle was practically flow-rate independent. In contrast, flow of nearly frictionless soft hydrogel spheres added drag to the gravitational force. The dependence of the total force on the obstacle diameter is qualitatively different for the two types of material: It grows quadratically with the obstacle diameter in the soft, low-friction material, while it grows much weaker, nearly linearly with the obstacle diameter, in the bed of glass spheres. In addition to the drag, the obstacle embedded in flowing low-friction soft particles experiences a total force from the top as if immersed in a hydrostatic pressure profile, but a much lower counterforce acting from below. In contrast, when embedded in frictional, hard particles, a strong pressure gradient forms near the upper obstacle surface.

Original languageEnglish
Article numberL062901
JournalPhysical Review E
Issue number6
Publication statusPublished - Dec 2023


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