[Xinyu Du]

Hi, I want to use Fluent to simulate the effect of ethylene dilution by N2 on carbon fume, but the Moss-Brooks model is based on methane study, and parameter correction is needed, what operation is needed to modify the carbon black nucleation rate constant in the Moss-Brooks carbon fume model? Is it programmed with UDF itself to set it? I hope you can give me an answer, thank you!

[fabiu50]

Hello!

I also worked a lot with these type of models. You can write UDFs to define nucleation rates for moss-brookes model in Fluent or you can simply type in fleunt terminal
"define/models/soot"
to activate soot model, and from then you can go to
"define/models/soot-parameters"
from here you can press enter and see all the options.
If you type in
"s-m-p" short for "soot-model-parameters" you can modify the constants for the Moss-Brookes model.

If you want to do some calibration for carbon black formation, this can be done by fitting the model with the aid of experimental data or taking a look at the "sticking coefficients" which is a specific coefficient to model soot formation for different fuels, and I imagine that your carbon black formation may come from a heavy fuel, so this may help you try to model it. Search for sticking coefficients in the Fluent Theory Guide, it will supply you with the original paper of this discussion.

Hope this helps.

[Arash_Fakharnezhad]

Hi Fabio

Could you please help me with the following issue if you are familiar with this model?

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/Se...ne_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.

https://i.postimg.cc/MTTs23BX/Picture1.png

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/Se...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?

https://i.postimg.cc/850Z1dd4/Picture2.png


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

Arash

[fabiu50]

Hello Arash,

This is rough without seeing the UDF itself.
Do not forget to include the
#include "udf.h"
#include "sg_pollut.h"
In the beggining of your UDF.

Anyway, this could be something to do with the version you are working on Fluent, and the version of the UDF manual as well.

In the worst case scenario, I think you could implement Moss-Brookes model completely via UDF. I have done it, it is simple. Here is my code, I literally copied what is done in Fluent Theory Guide.
I have done this in order to vary a lot of model constants at the same time, what was not possible via direct implementation on Fluent.

Hope it helps.

Fabio

[Arash_Fakharnezhad]

Hi Fabio,

Thank you for your reply.

An Ansys Employee replied to my question and I found that the UDF is actually only allowed for Pdf based combustion models. Here, I am using the species model to simulate the ethylene laminar diffusion flame! They mentioned that "this limitation is being removed for V 24.2 and it will be usable with species model as well in the future"

Thank you so much for your suggestion about implementing the Moss-Brookes model completely via UDS and UDF. Your code was really helpful and helped me understand how to do that. You saved me! I appreciate that.

Arash