UDF Source terms not producing expected results...
 

Hi, I'm hoping some people out there have had a similar experience with modling UDF source terms. My problem is the following:

2 streams with two separate fluids, separated by a solid, basically a conjugate heat transfer problem. The specifics are: 2-D axisymmetric, laminar, pressure-based solver, solving energy and multi-species transport, using the mixture model.

I model source terms in a UDF for each stream, the calculated source terms are exactly what they should be - I have checked with a calculator. If I set it so that there is exactly enough mass of a species coming into each stream, such that the source term uses all of that species up, such that there should be exactly zero mass left at the outlet, then I get an erroneous concentration profile. The simulation does not show expected behaviour... even if i set the mass fractions at the outlets, it doesn't have the right effect - there is still too much of one species in the stream.

I know my solution is wrong because I get the right solution for a different geometrical setup... this makes me think I have set something wrong in Fluent.

Any ideas what it might be?

Thanks,

Emmanuel