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Divergence in Two phase flow in impeller for Cavitation

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Old   November 5, 2014, 04:39
Default Divergence in Two phase flow in impeller for Cavitation
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Azarbayjan-e Sharqi (East Azerbaijan)
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Hi Dear Friends
We are simulating the cavitation in an impeller, but unfortunately the solution diverges:
Do you have any recommendation

iter continuity x-velocity y-velocity z-velocity k epsilon vf-phase-2 time/iter

reversed flow in 184 faces on pressure-outlet 7.
1 1.0000e+00 2.2754e-01 2.0786e-03 2.2741e-01 1.6760e+02 1.7002e+03 0.0000e+00 48:34:52 9999

turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 2 cells

reversed flow in 135 faces on pressure-outlet 7.
2 3.9495e-01 2.1120e-01 5.1330e-02 2.0287e-01 3.4835e-01 1.0742e+00 0.0000e+00 52:44:50 9998

reversed flow in 136 faces on pressure-outlet 7.
3 4.8944e-01 1.9892e-01 7.2566e-02 1.8881e-01 2.4924e-01 7.2195e-01 0.0000e+00 52:44:45 9997

reversed flow in 158 faces on pressure-outlet 7.
4 4.1480e-01 1.1867e-01 5.1597e-02 1.2584e-01 1.3764e-01 2.6765e-01 0.0000e+00 53:17:57 9996

reversed flow in 163 faces on pressure-outlet 7.
5 4.4587e-01 1.2438e-01 6.2952e-02 1.2580e-01 1.0816e-01 2.0903e-01 0.0000e+00 53:11:07 9995

reversed flow in 163 faces on pressure-outlet 7.
6 4.4594e-01 1.2414e-01 9.4380e-02 1.3768e-01 2.3518e-01 3.0147e-01 0.0000e+00 53:38:54 9994

turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 11 cells

reversed flow in 162 faces on pressure-outlet 7.
7 7.3659e-01 1.0458e-01 1.5275e-01 9.0316e-02 2.9884e+01 8.1153e+02 4.9588e-04 49:34:35 9993

reversed flow in 180 faces on pressure-outlet 7.

turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 198 cells
8 1.2326e+01 1.4642e-01 1.9726e-01 1.2146e-01 7.8176e+02 2.2140e+06 3.9421e-01 46:19:07 9992

reversed flow in 244 faces on pressure-outlet 7.

turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 6369 cells
9 2.0270e+03 3.6374e-02 2.0211e-01 7.3595e-02 2.5758e+03 4.9818e+07 2.3196e-01 43:09:24 9991
# Divergence detected in AMG solver: k -> Increasing relaxation sweeps!
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Old   November 5, 2014, 08:10
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Paritosh Vasava
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There are several reasons for divergence of AMG solver. Your mesh is too coarse, time-step is too large, turbulence boundary conditions not specified correctly and so on.

Also you may want to look at the turbulent viscosity. Although it is very common to have the turbulent viscosity limited to viscosity ratio of 1.000000e+05 warning but if it is not disappearing by the iterations then it is a matter of concern. You can plot turbulent viscosity or viscosity ratio and see where it is high and refine mesh in that region.
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Old   November 5, 2014, 09:33
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I am trying to model two phase of fluid in impeller the primary phase is water second is vapor water
Below is the last result that I got at the final iteration:
How should the vf-phase-2 progress in iteration?...
Thanks



iter continuity x-velocity y-velocity z-velocity k epsilon
vf-phase-2 time/iter
AMG on GPGPU
11 7.7680e+04 5.7695e-02 9.2269e-02 9.3629e-02 3.7974e+01 2.8999e+05 9.3219e-02 25:42:53 9989
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