Drag force granular temperature

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. 

Within CFD-DEM, the granular temperature is a smoothed macroscopic variable. So this addition will shift the average, but not influence the variability. Clearly, the difference between variabihty of the individual particle drag force experienced in DNS and CFD-DEM is due to the smoothed nature of the unresolved flow field in CFD-DEM. 

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