Multiphase Eulerian Gas-Solid Flow

Ssn

Dear All,

I try to simulate gas-solid flow (w/o any reaction) in a 7m-riser with Fluent 6.3 - Eulerian multiphase model (with single solid phase). Air is fed from bottom and solids as side inlets above 0.5 m gas inlet. I have quite a dilute flow (10kg/m2s). Main points of my model:

Solver: unsteady (transient) â€" 2D

Solution Controls: URFs = Defaults

Discretization = First-Order Upwind

Granular Temperature Model: Partial Differential Equation

Gas-Solid Drag : Gidaspow

Viscous model: k-epsilon

k-Epsilon model: Realizable / dispersed

Near-wall treatment: standard wall functions

(No UDFs used for turbulent viscosities)

My current mesh with boundary layer is fine enough. 50 elements in radial direction.

Time step: 1*10**(-4) max. iter. 30 (slowly increased to this and kept constant)

My problem is simulation goes quite well and converges at every time step in the beginning. And particles rise within the riser. After 1-1.5 sec, particles start to get collected near the walls (below 2 m of outlet line). And when it gets dense enough (like a layer/dead zone with a thickness of 20-30 cm), particles suddenly collapse and leave riser from bottom/gas inlet. And I am 100% sure that I am well above choking regime.

Unfortunately I couldn't find a solution for this. Does anyone has a similar experience? And any idea how to solve this case?

Thanks in advance,