Anisotropic orthotropic species diffusivity
 

Hi,

Does anybody have an idea how anisotropic or orthotropic species diffusion coeffients can be used in FLUENT via UDFs. I searched everywhere but did not find any information about this issue.

thanks.

Hi again Gemini ,

You can try to implement your species as UDS's, then use DEFINE_ANISOTROPIC_DIFFUSIVITY to define you diffusion coefficients. (I know that this will be really hard if you have more than 6 or 7 species).
To account for reactions, you can add thier effect as sources in the energy and the species equations.

Regards,
MJ

Hi MJ :)

I think the only way to implement anisotropic species diffusivity is the way you stated. FLUENT has drawbacks in this point and also definition of diffusion coefficients in full multicomponent diffusion.

I was considered the way you mentioned above before, but I am in the last six months of my work and I am not sure that I can handle the equations for 4 species in this limited time (numerical stability etc.). Also, in my work I always faced up limitations of FLUENT, so I am hesitating to implement my custom species transport balance.

Anyway, for example if I try to implement species transport as UDS, I think, I

- need to define new fluid material without having species transport enabled and momentum+energy balance activated.

- need to write density, viscosity, thermal conductivity, molecular weight, Cp, UDFs without accessing fluent database since without enabling species transport I assume that I have no access to Fluent database indise UDF

- need to write diffusion coefficient udfs

- need to learn how to implement energy source due to species transport. In this case definition of Cp is sufficient?

is there any point that I missed?

Thank you.

Best wishes,
Gemini

I think this is all. I am not sure if you need also to account for enthalpy of formation as a source term in the energy equation.

good luck,
MJ

Thank you MJ, I'm working on it, I will write here if I came up any interesting issues about modeling.

bye..

Have you solved the problem? I need help in the same.