Influence of an inserted bar on the flow regimes in the hopper* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11705256 and 11905272), National Postdoctoral Program for Innovative Talents, China (Grant No. BX201700258), and West Light Foundation of the Chinese Academy of Sciences (Grant No. 2018-98).

Abstract

We investigated the influence of an inserted bar on the hopper flow experimentally. Three geometrical parameters, size of upper outlet D 1, size of lower outlet D 0, and the height of bar H, are variables here. With varying H we found three regimes: one transition from clogging to a surface flow and another transition from a surface flow to a dense flow. For the dense flow, the flow rate follows Beverloo’s law and there is a saturation of inclination of free surface θ. We plotted the velocity field and there is a uniform linear relation between the particle velocity and depth from the free surface. We also found that the required value of D 1 to guarantee the connectivity of flow is little smaller than D 0. For the transition from a surface flow to a dense flow, there is a jump of flow rate and the minimum θ for flowing is two degrees larger than the repose angle.