[idomeneo]

Hi everybody,
I have a doubt about defining the boundary condition at outlet for a progress variable in a non-premixed combustion simulation case.
Actually, my progress variable Y is defined as linear combination of 3 species mass fractions and it is implemented through a UDS transport equation.
I've set the outlet boundary as pressure-outlet. Since I've already set Y as constant for coflow and fuel BC (calculated respect to the species mass fractions values of these inlets), now i'm not sure about what kind of BC i need to choose for the oulet: since the 2 possibilities for UDS boundary conditions are SPECIFIED VALUE and SPECIFIED FLUX, which one could be more suitable for this kind of simulation?

I sincerely appreciate any kind of suggestion.