Disentangling the free fall arch paradox in silo discharge

S.M. Rubio-Largo, Alvaro Janda, D Maza, I Zuriguel, R.C Hidalgo

Research output: Contribution to journalArticlepeer-review


Several theoretical predictions of the mass flow rate of granular media discharged from a silo are based on the spontaneous development of a free fall arch region whose existence is still controversial. In this work, we study
experimentally and numerically the particle flow through an orifice placed at the bottom of 2D and 3D silos. The implementation of a coarse grained technique allows a thorough description of all the kinetic and micromechanical properties of the particle flow in the outlet proximities. Despite the free fall arch does not exist as traditionally understood –a region above which particles have negligible velocity and below which particles fall solely under gravity action– we discover that the kinetic pressure displays a well defined transition in a position that scales with the outlet size. This universal scaling explains why the free fall arch picture has served as an approximation to describe the flow rate in the discharge of silos.
Original languageEnglish
Article number238002
JournalPhysical Review Letters
Publication statusPublished - 11 Jun 2015

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