Learning Forum

[orland_one]

Hello,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?Thank youn

[Surya Deb]

Hello, nSpecularity coefficient is a measure of the amount of tangential momentum that is imparted by the particles to the walls. So theoretically, a value of 0 means full slip and a value of 1 means no slip conditions.nThe specularity coefficient will also have an effect on the volume fraction of particles near the walls. nSince this is a fluidized bed simulation, I am hoping that you are comparing time averaged results. nCan you check if changing the specularity coefficient changes time averaged volume fraction and velocity distributions?nYou can use 3 different specularity coefficients to test : 0.006, 0.06 and 0.6 , respectively to get an idea.nAlso make sure to have a good ball park estimate of the particle friction factor.nRegards,nSuryann

[orland_one]

Currrenly, I don't have any avaraged result yet. The issue however remains. If I put specularity = 0, I should get a certain velocity along the wall, different from zero. This doesn't happen. n

[Seek]

Hi All,

I am having same trouble in understanding the velocity results after applying non-zero specularity values. The instant velocities are indeed zero on the walls. I would appreciate if someone has found explanation for this and can discuss here.

Regards-