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-   -   Multiphase phase (gas-solid) flow using Eulerian-Granular medel ( divergence problem) (http://www.cfd-online.com/Forums/fluent/84395-multiphase-phase-gas-solid-flow-using-eulerian-granular-medel-divergence-problem.html)

 jessie January 27, 2011 22:45

Multiphase phase (gas-solid) flow using Eulerian-Granular medel ( divergence problem)

Hello everyone,

I'm facing a problem in modeling a FCC riser. I am using an Eulerian granular multiphase model to simulate the flow pattern. A 3-D, steady state, k-e turbulent, non-reacting, isothermal flow is being simulated using the E approach. There are two phases in the riser right now, gas and solid. There are two different gases flowing into the system from two different inlets and the particle feed into the riser from one of the inlets.

The problem is when I change the drag coefficient relationship between the two gases and the particle from schiller-naumann to syamlal-obrien, the case just diverged. I already tried different meshes and reduced the relaxation factor, however there is no improve at all. The fluent showed "Divergence detected in AMG solver: mp-x-momentum -> Decreasing coarsening group size!......"

If I just use the schiller-naumann, the case can converge. And if I just simulate the flow of one gas and the particle using syamlal-obrien or two gases, at least the case would not be diverged. Does anyone have any idea why this is happening and how can I fix it?

 Angeline January 28, 2011 02:09

 jessie January 28, 2011 11:09

Quote:
 Originally Posted by Angeline (Post 292583) use unsteady simulation.......
Hello Angeline,
I tried unsteady condition, but the case still diverged.

 jipaz May 29, 2014 11:05

Hi Jessie:

I have almost the same problem, I'm simulating a 2D riser with two phases gas-solid. I've been using Syamlal-O'Brien drag model until now and everything has run ok.

The I changed the drag model to EMMS, and I got

# Divergence detected in AMG solver: mp-x-momentum -> Decreasing coarsening group size!

Divergence detected in AMG solver: pressure correction

at the very beginnig of the simulation, it does not start to converge.

Every previous research work sets as inital conditions that "no gas or air into the riser" so I understood that Vg=0, Vs=0, and vol fraccion of solids=0, what it means that at the begginig the riser is full of static air, and not solids at all.

I changed the initial condition setting Vg=5.2 m/s, and the simulation runs for 3-4 iterations but it crashses again, now only with

Divergence detected in AMG solver: pressure correction, error.

Is correct to set Vg=0, Vs=0, and vol fraction of solids=0 when "no gas or air into the riser" is said?

Ignacio

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