DEFINE_SOURCE cancellation??

mCiFlDk · May 2, 2020, 15:05

Hi everyone,

My doubt concerns the interpretation that ANSYS does to the DEFINE_SOURCE macro, and how it is related to the User-defined Scalar transport equation. Last time I used this function, it was together with a non-zero diffusivity coefficient while simulating plasma, and I don't know if I should use DEFINE_SOURCE again if I'm not solving any kind of partial diff eq.

The equation I'm using is pretty simple (attached below); it only has two variables (x and y) that are referred to the position of the point on which it would be applied and the rest are constant values.

Thanks in advance.

vinerm · May 2, 2020, 16:01

Source terms are used to model generation or depletion of some field due to a reason that is not included in the simulation. What you have is an algebraic equation and can be modeled using a custom-field-function. You do not require a UDF.

mCiFlDk · May 2, 2020, 16:28

Quote:

Originally Posted by vinerm

Source terms are used to model generation or depletion of some field due to a reason that is not included in the simulation. What you have is an algebraic equation and can be modeled using a custom-field-function. You do not require a UDF.

Thanks a lot for the quick response. I've opened Fluent and I've been looking for the field functions that can be applied by the custom field. Sadly, body force [N/m^3] is not included within the options.

I'm even more confused, but as DEFINE_SOURCE is defined by [N/m^3] I thought it was the correct way to do it.

I'll wait for your reply. Thanks a lot

vinerm · May 2, 2020, 16:31

Where is body force being used in the equation? Do you mean the thrust? Fluent only reports field variables and not integrals, which you might need. In that case, you have to write an expression instead of CFF.

mCiFlDk · May 2, 2020, 16:40

Quote:

Originally Posted by vinerm

Where is body force being used in the equation? Do you mean the thrust? Fluent only reports field variables and not integrals, which you might need. In that case, you have to write an expression instead of CFF.

Yes, that's exactly what I meant. The equation output is thrust. Then I'll need a simple UDF where DEFINE_SOURCE is used or I'll need another macro? Because that is my headache.

Thank you.

vinerm · May 2, 2020, 16:42

Output doesn't matter. There is a thrust component in the equation, which is multiplied with $\pi^2$ , what is that? Is that a constant or do you want that to be determined based on some field in the Fluent?

mCiFlDk · May 2, 2020, 16:59

Quote:

Originally Posted by vinerm

Output doesn't matter. There is a thrust component in the equation, which is multiplied with $\pi^2$ , what is that? Is that a constant or do you want that to be determined based on some field in the Fluent?

This equation is defining the maximum thrust per unit depth in X axis that is produced by a plasma actuator. This term has to be applied directly as a source term to the NS equations, and is constant through time, it doesn't depend on any field apart from the distances x and y respect to a point defined by the user.

vinerm · May 2, 2020, 17:01

I'd recommend you to read my first post again.

You need to use DEFINE_SOURCE.

mCiFlDk · May 2, 2020, 17:09

Quote:

Originally Posted by vinerm

I'd recommend you to read my first post again.

You need to use DEFINE_SOURCE.

I've read it and yes, you're right.

Thanks a lot Vinerm

May 2, 2020, 16:01	Define_source	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Source terms are used to model generation or depletion of some field due to a reason that is not included in the simulation. What you have is an algebraic equation and can be modeled using a custom-field-function. You do not require a UDF. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 2, 2020, 16:31	Body Force	#4
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Where is body force being used in the equation? Do you mean the thrust? Fluent only reports field variables and not integrals, which you might need. In that case, you have to write an expression instead of CFF. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 2, 2020, 16:42	Thrust	#6
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Output doesn't matter. There is a thrust component in the equation, which is multiplied with $\pi^2$ , what is that? Is that a constant or do you want that to be determined based on some field in the Fluent? __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

May 2, 2020, 17:01	Source Term	#8
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	I'd recommend you to read my first post again. You need to use DEFINE_SOURCE. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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