Initial- and Boundary Conditions for Particle Phase Equations

6 Initial- and Boundary Conditions for Particle Phase Equations 

To solve the equations of granular flows, appropriate boundary conditions for the velocities and for the granular temperature are required. The boundary conditions proposed by Ding and Gidaspow [30] are generally adopted in most granular flow simulations. 

At the impermeable wall, the no-slip condition is generally not appropriate for granular flows. Nevertheless, the granular phase velocity component normal to the wall is normally set to zero. However, the granular phase is usually allowed to slip along the wall. A velocity slip proportional to the velocity gradient at the wall is 

The slip parameter takes the value of the mean free path of the molecules. Xd is normally estimated by  

Although there might be a granular temperature flux through the wall, little is known about the magnitude of such a flux. Hence, a simple zero gradient boundary condition 

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