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Old   December 17, 2004, 09:48
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Dear Users

I am doing two phase simulations in pipe, the simulation ran during which i am experiencing below problems:

1.continuity equation residual that does not lowers below 10-1.

2. Turbulent viscosity limited to viscosity ratio 10+5 initailly to only few cells less than 24 which goes away after some 50 iterations ......but stays constant if i run the case with conidtion as in below case.

3. If i keep backflow volume fraction of air from exit of pipe to be 0.2 it works and if i change it to 1 meaning that none of air reenters pipe than my case diverges. and i receive following messages.

i.e Halting due to end of file on input.

Error: > (greater-than): invalid argument [2]: wrong type [not a number] Error Object: inf

can any one suggest what might be the solution of this?

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Old   December 17, 2004, 18:23
Default Re: error messages
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1) The problem with the continuity residual could be related to improper boundary conditions, but usually it is related to the solver settings.

Try to reduce the momentum under relaxation factor to 0.4 and to increase the pressure under relaxaztion factor to 0.5 or 0.6. Reduce turbulent variables under relaxation factor to 0.4 but *do not* under-relax turbulent viscosity (keep the underrelaxation factor equal to 1).

2) If the turbulent viscosity limitation disappears after a few iteration, it's ok.

3) FLUENT asks you the backflow volume fraction only for secondary phases. If you set the backflow volume fraction equal to 1, all the secondary phase will re-enter the pipe in the case of reversed flow. If you don't want air to re-enter the pipe, you have to set its backflow volume fraction to 0.


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Old   February 19, 2011, 07:30
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How can i set outlet volume fraction when set set pressure outlet?
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