The Beverloo's scaling for the gravity flow of granular materials throughorifices has two distinct universal features. On the one hand, much highlightedin the literature, the flow rate is independent of the height of the granularcolumn. On the other hand, less celebrated yet more striking, the flow rate isfairly insensitive to the material properties of the grains (density, Young'smodulus, friction coefficient, etc.). We show that both universal features arelost if work is done on the system at a high rate. In contrast with viscousfluids, the flow rate increases during discharge if a constant pressure isapplied to the free surface of a granular column. Moreover, the flow ratebecomes sensitive to the material properties. Nevertheless, a new universalfeature emerges: the dissipated power scaled by the mean pressure and the flowrate follows a master curve for all conditions of forcing and materialproperties studied. We show that this feature can be explained if the granularflow in the silo is assumed to be a quasistatic shear flow.
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