Learning Forum

[FidelCsB]

Hi everyone.

I'm trying to simulate an electro osmotic flow on Fluent. Does anyone know if it is posible??
I recently discover the MHD module, but I need the Poisson Equation and this model neglected the electric charge density and I need it for my simulation. Maybe with a UDS I could simulate it, but I don't know if the new variable is independent from the other governing equations because I need it inside them.

Thanks in advance.

[Karthik R]

Hello,

If I understand your problem correct, you can certainly use the UDS as an additional equation in Fluent. You can bring the new variable into the other governing equations as sources terms. Please note that these source terms are volumetric and need to be linearized. You can code these sources terms as UDFs and incorporate the variable into other governing equations.

Please let us know if you have any more specific questions.

Thank you.

Best Regards,

Karthik

[FidelCsB]

Thanks Karthik, that could be a solution for my problem. Just two more question, how can I linearized those source terms? and wich macro I need to use for my UDF? 

[Karthik R]

Hello,

Please have a look at the following screenshot from the Fluent Customization Manual I am embedding here. This is in the section on DEFINE_SOURCE in the manual, which is the UDF macro you will be using to define source terms in Fluent. This screenshot briefly discusses on source term linearization.

I hope this helps.

Thank you.

Best Regards,

Karthik

[FidelCsB]

I have another question about the source and the macro, can I bring the same variable that the UDS is solving into its source term??

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This is my equation. I have the variable in the diffusive term and in the source so my UDF for the source needs the same variable, it is posible? I've read in the fluent documentation I can access to the cell variables with C_UDSI macro but I'm not sure if I can access to the same variable.
Thanks for read, hope you can answer

[Karthik R]

Hello,

Yes, you can do this. You should be able to access this variable from the previous iteration for your source term. You can store the previous solution of 'phi' in a UDMI and access this to estimate the source term to solve the next iteration. I hope this helps.

Thanks.

Best Regards,

Karthik