{"id":168762,"date":"2022-04-22T08:35:18","date_gmt":"2022-04-22T08:35:18","guid":{"rendered":"\/forum\/forums\/topic\/solid-gas-granular-mixture-rapidly-diverging-after-100-iterations\/"},"modified":"2022-05-04T11:27:01","modified_gmt":"2022-05-04T11:27:01","slug":"solid-gas-granular-mixture-rapidly-diverging-after-100-iterations","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/solid-gas-granular-mixture-rapidly-diverging-after-100-iterations\/","title":{"rendered":"Solid-Gas granular mixture rapidly diverging after 100 iterations"},"content":{"rendered":"
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Hi,<\/p>\n

I am simulating a steady multiphase flow case, consisting of air and sawdust particles, using the ganular mixture model, but the simulation rapidly diverges after approx. 100 iterations. <\/p>\n

My Setup: The density ratio is rho_p\/rho_f=700, with d_p=1E-6 m and a volume fraction of 10% at the inlet. I am using the Syamlal Obrien Model for the granular viscosity. All other settings are kept the same. <\/p>\n

I am using the coupled solver with Presto, QUICK and second-order discretizations, when available. For turbulence I am using the k-omega SST model. I tried it with coupled or SIMPLEC, but for both cases it diverged.<\/p>\n

The geometry is the air surrounding a disc (the saw with 150 mm), a curved housing and a suction tube with diameter D=75 mm. The boundary condition on the surface of the disc is defined as velocity inlet, using a velocity profile obtained from a simulation with the real saw geometry. For simplicity, it can be assumed as the tangential velocity of the saw (40 m\/s) and a lower radial component of about 10 m\/s. The second phase enters the domain through the curved surface of the disc with a thickness of 10 mm, and leaves the domain through the suction tube, where a pressure oulet condition with -700 Pa results in a mean velocity of 20 m\/s. The surrounding was set as a pressure inlet with P=0 Pa. Gravity is active in -y direction.<\/p>\n

The mesh is refined around the disc, with an element size of 0.4 mm and gets coarser as it gets away from the disc (3 mm). I am using a tetahedral mesh, without prism layers.<\/p>\n

The residues stay at a stable level (around 1E-2 to 1E-3) up to approx. 100 iterations where the residue of k and omega just jump to 1E0, 1E4 and up to 1E71, as in the figure: <\/p>\n

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\n\"divergence.png\"
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