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-   -   DO Model giving wrong results for optically thick media ? (https://www.cfd-online.com/Forums/fluent/83682-do-model-giving-wrong-results-optically-thick-media.html)

pprllo January 7, 2011 09:58

DO Model giving wrong results for optically thick media ?
 
First of all, hello everyone as this is my first post here ! :D

Now, the problem.

I set up a very simple case, 2 walls at set temperature separated by a fluid. No gravity. No scattering.

Then i tried solving it:
- Without radiation
- With Rosseland radiation model.
- With P-1 radiation model.
- With DO radiation model.

Well, while Rosseland and P-1 results are consistent across a range of temperatures and absorption coefficient, I noticed that the wall fluxes calculated with the DO model are always higher than those calculated with Rosseland or P-1.

At this point i set the absorption coefficient at an extremely high value (10^9) and, while the Rosseland and P-1 models give me the predictable result (i.e. radiation heat transfer become negligible), the DO model still gives very high values of radiation heat transfer.

Any ideas ?

pprllo January 11, 2011 16:39

Upping the thread. Maybe someone has an idea. :D

Nikolopoulos January 21, 2011 13:45

Which version of fluent are you using?

i_flying April 16, 2013 21:27

Quote:

Originally Posted by pprllo (Post 289601)
First of all, hello everyone as this is my first post here ! :D

Now, the problem.

I set up a very simple case, 2 walls at set temperature separated by a fluid. No gravity. No scattering.

Then i tried solving it:
- Without radiation
- With Rosseland radiation model.
- With P-1 radiation model.
- With DO radiation model.

Well, while Rosseland and P-1 results are consistent across a range of temperatures and absorption coefficient, I noticed that the wall fluxes calculated with the DO model are always higher than those calculated with Rosseland or P-1.

At this point i set the absorption coefficient at an extremely high value (10^9) and, while the Rosseland and P-1 models give me the predictable result (i.e. radiation heat transfer become negligible), the DO model still gives very high values of radiation heat transfer.

Any ideas ?

I have get the same answer as you said, and when the optical thickness is very large, the convergence by do model with do/energy coupled is very fast , the P1 model is very low. which model you selected last?


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