I am currently simulating a fluidized bed reactor. The flow field is laminar. I am using a Eulerian Eulerian model with algebraic granular temperature formulation, Gidaspow drag model and the typical models for bulk, granular viscosity ecc. As for the boundary conditions at the wall I imposed a specularity coefficient of 0.6.
Now, when I analyze simulation's results I can see that even if I am actually imposing a partial slip boundary condition at the wall, the axial velocity of the solid particles is always equal to zero. Even if I change the values of the specularity coefficient, nothing seems to change. The only way to have an actual slip along the walls is to impose a zero shear stress at the wall.
Could you help me understand why velocity is always equal to zero? Is it wrong?