Luke Fullard (Massey Univ, NZ) - Transients in dense granular flow: an experimental, numerical, and modelling study

Mathematical modelling of the flow of a dense granular material in a hopper, silo, or bunker has been a topic of interest for some time. Models, such as the kinematic model, describing such flow often assume that the solids fraction is constant in the system. Additionally, the flow is usually assumed to be at steady state, and there is little work in the literature about transients in simple granular flow systems. We perform x-ray fluoroscopy and particle image velocimetry (PIV) experiments to observe the development of the flow profile. It was found that the system has three transients: 1) a very rapid (less than a second) transition from zero mass flow rate to the Beverloo rate, 2) a longer (of the order of a minute) transient to steady state flow, after which the system velocity is constant in space and time, and 3) an initial rapid vertical dilation wave. During this transient period, we observe the rapid development of a dilation wave, whose vertical velocity was at least an order of magnitude higher than the flow velocity. We also introduce a method to approximate the solids fraction using the PIV measurements and the known initial packing fraction, and we contextualize our work by the discussion of transient and steady state measurement of residence time distributions in such systems. Finally, I outline some related future research goals for the purpose of stimulating discussion about potential solutions approaches.