Granular shear flow dynamics and forces: Experiment and continuum theory

摘要

We analyze the main features of granular shear flow through experimentalmeasurements in a Couette geometry and a comparison to a locally Newtonian,continuum model of granular flow. The model is based on earlier hydrodynamicmodels, adjusted to take into account the experimentally observed couplingbetween fluctuations in particle motion and mean-flow properties.Experimentally, the local velocity fluctuations are found to vary as a power ofthe local velocity gradient. This can be explained by an effective viscositythat diverges more rapidly as the random-close-packing density is approachedthan is predicted by Enskog theory for dense hard sphere systems. Experimentand theory are in good agreement, especially for the following key features ofgranular flow: The flow is confined to a small shear band, fluctuations decayapproximately exponentially away from the sheared wall, and the shear stress isapproximately independent of shear rate. The functional forms of the velocityand fluctuation profiles predicted by the model agree with the experimentalresults.