[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.

[m20]

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.

[hossein65]

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

[raju.vadlakonda]

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??

[m20]

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??

Please have a look on following thread:
http://www.cfd-online.com/Forums/flu...ying-lift.html

[raju.vadlakonda]

Originally Posted by m20

Please have a look on following thread:
http://www.cfd-online.com/Forums/flu...ying-lift.html

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

[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)

[raju.vadlakonda]

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 :-)

[yuvarajp]

Originally Posted by raju.vadlakonda

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

hi,

im also having the same issues. did u find any solution?