Learning Forum

[afakharnezha]

Hello, 

I'm currently utilizing the Moss-Brookes model within the species model framework for predicting soot. While the model performs adequately, I'm interested in incorporating my own nucleation rate using the User-Defined Function (UDF) option provided by the Moss-Brookes model. Despite implementing the UDF template exactly as provided in the UDF manual (https://ansyshelp.ansys.com/Views/Secured/corp/v231/en/flu_udf/flu_udf_ModelSpecificDEFINE.html#flu_udf_sec_define_soot_nuclei), it appears that the Fluent solver is disregarding it. Even when I modify values or add print commands within the UDF file, there's no observable change in the nucleation rate or any output in the console.

It's worth noting that when I utilize the soot oxidation model within the model settings, using the template in the UDF manual for soot oxidation rate (https://ansyshelp.ansys.com/Views/Secured/corp/v231/en/flu_udf/flu_udf_ModelSpecificDEFINE.html#flu_udf_sec_define_soot_oxidation), it operates as expected showing that compiling process is fine! However, as I mentioned earlier the user-defined soot nuclei rates or user-defined soot mass rate seem to be ineffective! Has anyone successfully employed this option (User Defined Functions) before? Is there something crucial that I might have overlooked?

 

 

I'd greatly appreciate any insights or assistance regarding this matter.

 

 

[afakharnezha]

Just a friendly bump to see if anyone has any thoughts on "Soot_Moss-Brookes_UDF"

Arash

[jcooper]

Hi Arash:

It turns out that here are two issues here 

 

1. The UDF is actually only allowed for Pdf based combustion models. This limitation is being removed for V 24.2 and it will be usable with species model as well in the future
2. The UDF example in the tutorial guide is only valid when the nucleation precursor species is chosen from the available species (species that are part of mixture or pdf mixture). The UDF will NOT work with precursor correlations. In principle, it could work with any method, but implementing nucleation for a precursor correlation is quite a bit more involves and would reveal too much in-house code.

We will modify the documentation to clarify these points.

 

Best Regards,

Judy

[afakharnezha]

Hi Judy,

Thank you for your reply.

It seems that in my case, the issue is likely related to the first point you mentioned. I am attempting to simulate an ethylene laminar diffusion flame using the species transport model. However, regarding implementing the soot model with a UDF, I can confirm that I am choosing nucleation precursor species from the available species option!

I am relatively new to combustion in Fluent, and it appears that "Pdf based combustion models" are not applicable for laminar conditions. What about using a UDF in the method of moments for soot dynamic? I wonder if the same limitation applies.

Additionally, I would appreciate it if you could suggest an alternative option for accounting for soot dynamics while allowing me to incorporate my own soot nucleation rate.

Best regards,

Arash

[jcooper]

Yes, it does.  Sorry, I don't know of any alternate methods for incorporating soot nucleation.  I would conduct a literature study to see what others have done.

Best Regards,

 

Judy

[afakharnezha]

Thank you Judy and you were right, the UDF option for the method of moments does not function with the transport species model, as you mentioned.

I’m glad to hear that this limitation is set to be resolved in version 24.2. Could you please provide information on the release date for this version? Additionally, can you confirm that this limitation indeed be addressed in V 24.2? I ask because I need to plan my PhD project accordingly however I’m also exploring alternative options.

Regards,

Arash

[jcooper]

Hi Arash:

The *.2 releases are usually around the mid-year mark.  I don't think there is an official date yet.  The limitation is supposed to be addressed, but, as with any new changes that does not preclude problems under certain conditions.  I would advise checking with your model conditions as soon as the release becomes available.

Best Regards,

Judy