Learning Forum

[Anshul Chandel]

Hi 

I am trying to simulate methane pyrolysis in a reactor chamber using the species from ARAMCO 3.0 mechanism. The problem has 38 reactions and 21 species including C, H, Ar and various C1-C6 hydrocarbons. The model works with all the reactions (36) except for the carbon formation reactions (2). When I try to add Carbon in the species list and add Carbon formation reactions, Fluent crashes and gives the following error in the error log file:

Error [node 999999] [time 2/20/24 15:24:55] Abnormal Exit!

I also see a long list of NaN values before it crashes. Does anyone have an idea why this is happening and how I can successfully add Carbon formation reactions to the model. 

I am using Fluent 2022 R2 on 36 cores. Carbon forming reactions: 

C6H6 = 6C + 3H2 0.75E+5 0 41730

C2H2 + C = 3C + H2 5E+7 0 24044

Thank you

[jcooper]

Hi Anshul:

At what point does Fluent crash?  Does it crash while processing the mechanism, or at run time?

Usually problems with mechanisms occur while the mechanism is read in.  I would check the output from the mechanism preprocessing to be sure there are no errors in the mechanism files.  Mechanism proprocessing output is written to files in the Fluent working directory after the mechanism is imported.

There may also be problem with the thermodynamic data for carbon. There are several different forms of "C", so it is important to reference the correct thermodynamic data, depending on the state of carbon. I would use one of the thermo files that comes with Chemkin for your carbon species.  This is part of the Chemkin installation and can be accessed without a license.  One example of such a file is  mixedcase_therm.dat, which resides in the... ANSYS Inc\v232\reaction\data folder. This file contains C(s) as well as other forms of carbon.

I hope this helps.

Best Regards,

Judy

 

Best Regards,

Judy

[Anshul Chandel]

Hi Judy

Thank you for replying to my question. Fluent crashes at run time after the first few iterations. 

I checked the output file to check and there were no errors in it. Please see the attached screenshot of the output file.

I was not able to find the specific file that you had mentioned but I was able to find a similar file named, grimech30_thermo.dat and when I replaced  C properties in my thermo file using that file, Fluent still crashed same as before.

I went ahead and found C(s) properties from the 'Chemkin Thermodynamic Database' from https://www.osti.gov/servlets/purl/7073290 and tried to replace that in my file and it still did not make a difference. Fluent crashed after the first few iterations again. 

One thing noticed was whenever I import the chemkin files, Fluent gives the warning: 

 

Do you think this might be the culprit? If not, do you have any other ideas that I can look into?

Thank you. Regards.

Anshul

[jcooper]

HI Anshul:

That error does not usually cause a problem.  Can you please show me the output from the Fluent window?  Please restart the run and include a screenshot of everything that happens from the before the start of the first iteration.

If you know when the crash is going to happen, you can also try stopping one iteration earlier and writing out a solution file.  Post processing the results for species mnass fractions and temperature may also give some clues.

Best Regards,