A bunker is a combination of a bin and a hopper (Fig. 1.5). The abrupt change in geometry at the bin–hopper transition results in a rich variety of flow patterns, and oscillatory wall stresses. These features pose formidable difficulties for modeling bunker flow. At present, there are no satisfactory models which can capture all the observed features.

Some of the experimental observations are summarized below. This is followed by a discussion of models for the bin section, the transition region, and the hopper section.

EXPERIMENTAL OBSERVATIONS

Flow Regimes

The patterns observed by Nguyen et al. (1980) for the flow of sand through a bunker are shown in Fig. 4.1. For θw < 40°, mass flow (type A) occurs regardless of the value of H/W (Fig. 4.2). Here W and H are the half-width of the bunker and the height of the free surface of the material relative to the exit slot, respectively. (For small values of H, the free surface is not flat. In this case, H is the elevation of the point of intersection of the free surface with the bunker wall.) For θw > 70°, funnel flow of type B occurs when H/W exceeds a critical value (≍3) and funnel flow of type C occurs for a smaller value of H/W. As indicated by the hatched regions in Fig. 4.2, the boundaries between various regimes are not sharply defined. For θw = 60°, there is an interesting transition from mass flow to funnel flow, and back again to mass flow as H/W decreases from high values.