Placing an obstacle in front of a bottleneck has been proposed as a sound alternative to improve the flow of discrete materials in a wide variety of scenarios. Nevertheless, the physical reasons behind this behavior are not fully understood and the suitability of this practice has been recently challenged for pedestrian evacuations. In this work, we experimentally demonstrate that for the case of inert grains discharging from a silo, an obstacle above the exit leads to a reduction of clog formation via two different mechanisms: i) an alteration of the kinematic properties in the outlet proximities that prevents the stabilization of arches; and ii) an introduction of a clear anisotropy in the contact fabric tensor that becomes relevant when working at a quasi-static regime. Then, both mechanisms are encompassed using a single formulation that could be inspiring for other, more complex, systems.
We experimentally demonstrate that an obstacle, when suitably placed above a bottleneck, leads to a reduction of clog formation in a silo via two different mechanisms. The first one, already suggested in previous works, is related to an alteration of the kinematic properties in the outlet proximities that prevents the stabilization of arches. The second, that is discovered when working at a quasi-static regime, appears because the obstacle induces a clear anisotropy in the contact fabric tensor. Then, both mechanisms are encompassed using a single equation in which two parameters -one related with the geometrical effects and the other to the kinematic ones- are enough to reproduce all the experimental results
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