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Bubble column simulation with Lift coefficient UDF

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Old   June 26, 2013, 03:55
Default Bubble column simulation with Lift coefficient UDF
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Balraju
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Hii ..

Iam doing two phase cfd simulations of bubble column in FLUENT.I want to study the effect of lift force,so i wrote UDF.when i running with UDF in FLUENT its getting divergence.While compiling UDF,its not showing any errors.How to overcome this problem??

Please suggest me.
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Old   June 29, 2013, 04:22
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Quote:
Originally Posted by raju.vadlakonda View Post
Hii ..

Iam doing two phase cfd simulations of bubble column in FLUENT.I want to study the effect of lift force,so i wrote UDF.when i running with UDF in FLUENT its getting divergence.While compiling UDF,its not showing any errors.How to overcome this problem??

Please suggest me.
I think there is nothing wrong with your UDF, just one coefficient in line 43:
"f1=0.0105*pow(mod_etvos,3)-0.0159*pow(mod_etvos,2)-0.0204*mod_etvos+0.474;"
This equation is Tomiyama' equation and the first coefficient is 0.00105 instead of .0105.
Getting convergence by considering lift force is not simple in bubble column and you should have a look on solution controls and AMG solver.
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Old   June 30, 2013, 00:41
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the problem of writing a UDF aside, did you obtain reasonable velocity distribution? because when I simulate a bubble column, every thing looks fine, except velocity. the inlet velocity is 0.1m/s (air) but after some time steps, the maximum velocity in the system goes to 1.1 m/s. it seems like a air jet in the inlet, so it messes every thing up
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Old   June 30, 2013, 05:58
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Quote:
Originally Posted by m20 View Post
I think there is nothing wrong with your UDF, just one coefficient in line 43:
"f1=0.0105*pow(mod_etvos,3)-0.0159*pow(mod_etvos,2)-0.0204*mod_etvos+0.474;"
This equation is Tomiyama' equation and the first coefficient is 0.00105 instead of .0105.
Getting convergence by considering lift force is not simple in bubble column and you should have a look on solution controls and AMG solver.
Hiii,

Yes,the first coefficient is 0.00105.
In simulations iam getting usually "Divergence detected in AMG solver". How to handle this problem??
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Old   June 30, 2013, 06:21
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Quote:
Originally Posted by raju.vadlakonda View Post
Hiii,

Yes,the first coefficient is 0.00105.
In simulations iam getting usually "Divergence detected in AMG solver". How to handle this problem??

Please have a look on following thread:
2 Phase flow - applying Lift
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Old   July 2, 2013, 02:25
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Originally Posted by m20 View Post
Please have a look on following thread:
2 Phase flow - applying Lift

Thank you for your help.

I have started simulations with that idea,but after some iterations simulation getting divergence.

The error is coming like this "turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 120589 cells ".

Please help me to overcome this problem.

Regards,
Raju
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Old   July 6, 2013, 08:47
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You can consider one of the following things:
1. Change AMG solver coefficients
2. Run the simulation in laminar condition at first then switch to turbulent
3. Do initialization with best initial guess (this Is very important)
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Old   July 11, 2013, 09:19
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Quote:
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You can consider one of the following things:
1. Change AMG solver coefficients
2. Run the simulation in laminar condition at first then switch to turbulent
3. Do initialization with best initial guess (this Is very important)
Thank u :-)
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