# Bubble column simulation with Lift coefficient UDF

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June 26, 2013, 03:55
Bubble column simulation with Lift coefficient UDF
#1
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Balraju
Join Date: Feb 2011
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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??

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 custom_lift.c (1.7 KB, 35 views)

June 29, 2013, 04:22
#2
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Quote:
 Originally Posted by raju.vadlakonda 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.

 June 30, 2013, 00:41 #3 Member   Hossein Join Date: Oct 2010 Location: Greensboro, NC, USA Posts: 30 Rep Power: 9 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 __________________ Hossein Amini PhD student in Biochemical Engineering; Computational Science and Engineering department; North Carolina Agricultural and Technical State University

June 30, 2013, 05:58
#4
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Balraju
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Quote:
 Originally Posted by m20 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??

June 30, 2013, 06:21
#5
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Quote:
 Originally Posted by raju.vadlakonda Hiii, Yes,the first coefficient is 0.00105. In simulations iam getting usually "Divergence detected in AMG solver". How to handle this problem??

http://www.cfd-online.com/Forums/flu...ying-lift.html

July 2, 2013, 02:25
#6
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Balraju
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Quote:
 Originally Posted by m20 Please have a look on following thread: http://www.cfd-online.com/Forums/flu...ying-lift.html

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 ".

Regards,
Raju

 July 6, 2013, 08:47 #7 New Member   Join Date: Nov 2012 Posts: 3 Rep Power: 7 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)

July 11, 2013, 09:19
#8
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Balraju
Join Date: Feb 2011
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Quote:
 Originally Posted by m20 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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