Abstract: We investigated the influence of an inserted bar on the hopper flow experimentally. Three geometrical parameters, size of upper outlet D₁, size of lower outlet D₀, 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 D₁ to guarantee the connectivity of flow is little smaller than D₀. 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.

Key words: hopper flow, inserted bar, flow type transition, free surface, velocity distribution