Wall boundary conditions granular flows

Jenkins JT (1992) Boundary Conditions for Rapid Granular Flow Flat, Frictional Walls. J Appl Mech - Trans ASME 59 120-127... 

In Fig. 3, the energy lost due to inelastic collisions and viscous gas are compared. For a mixture flow, compared with inelastic dissipation, the viscous dissipation is relatively small, especially in the region near the boundary wall. Hence it may be acceptable to neglect the effect of the drag force in establishing the boundary conditions. When the granular temperature decreases, the viscous dissipation becomes more important until it is, indeed, greater than the inelastic collision dissipation. 

Jenkins, J. T. 2001. Boundary conditions for collisional grain flows at bumpy, frictional walls. In Granular Gases, edn. T. Poschel and S. Ending, 125-138, Berlin, Germany Springer. 

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