Numerical study of free-fall arches in hopper flows

•DEM simulation of hopper flows were performed on GPUs.•The free-fall arch structures in hopper flows were plotted by statistical methods.•Spatial profiles in the hopper flows were investigated statistically.•The arch structure is consistent with the profiles but different from ideal FFAs.

Beverloo’s law describes the flow rate of grains discharging from hoppers, where the assumption of a free-fall arch (FFA) is very useful in understanding the physical picture of this process. The FFA has been observed in previous experiments but a clear systematic study of the FFA is still necessary. In this paper, dense granular flow in hoppers was studied by numerical simulations, in attempts to explore the free-fall region and its boundary. Generally, the numerical simulation results support the free-fall arch assumption, although the statistical description of the FFA is not exactly equivalent to its strict definition.