[pablop]

I have to create a boundary condition PROFILE in UDF, in which I can fix a UDSI value between two adjacent zones (like coupled walls) and at the same time create a discontinuity in the value of its flux. The trouble is that with only one interface (coupled walls) I can only set up one profile for fixing one of them.

I dont know if it is possible to create four adjacent interfaces for that purpose. Anyone has an idea?

[vinerm]

For the coupled walls, Fluent does not enforce conservation of flux. Those are just default conditions, for temperature as well as for UDS. User can choose different flux values on each side and even flux on one side and value on the other. Of course, then those are not coupled anymore.

[pablop]

Thank you for your message

I know that coupled walls does not mean conservation, what I want to do is set conservation on the scalar and at the same time establish a different flux on the wall but I can only chose between Neumann and Dirichlet b.c condition. It would be like introducing a flux source on the interface

[vinerm]

You can separate first layer of cells from the interface and apply a source term. Applying both, value and flux, may lead to conservation issues. Assuming this UDS represents energy, then applying a temperature and a heat flux may not maintain flux conservation with the other boundaries. So, source at the cells could be one way.

[pablop]

To clarify continuing with the energy equation analogy I should multiply the flux with the cell area and apply it as a source in the cell, no?

Thank you.

[vinerm]

Whenever a source is applied, it is always a volumetric source. Fluent will multiply this value with the cell volume and then apply it. A big difference in flux and source is that the flux is a vector while source is not. However, since you will apply source adjacent to the interface, it will automatically create gradient depending upon the field value in the adjacent cells. As far as value is concerned, you may have to iterate over it since you may know the flux value but flux will depend upon gradient. So, you have to try a few values of the source before you get it right.

[pablop]

I only know the difference in flux between the interface, so introducing this source which would represent the jump, should be sufficient. Ok thank you I will try

[vinerm]

Yes, the source would create a jump, however, you will have to fine tune the value of the source so that you get the desired jump.

[pablop]

Hi,
Thank you! It worked, by any chance do you know if it is possible to write a single source for momentum equation so that I can get the equation component from a macro, instead of writing 3 different sources for each component.

[vinerm]

Fluent doesn't care about what you write in source function and where do you hook. It will just use the values and apply it as source. So, you can hook same code as mass source, all three momentum source, energy source, etc.