I don't understand the BC of FLUENT, overdimension

friskies

Hi everybody,

I am trying to simulate a very easy problem in fluent. I have a single pipe full of water with one specie. I have a velocity inlet defined at 1.07. I want to introduce a variation function in the inlet for the mass fraction of the specie. The problem is that the outflow boundary condition is not working. It gives me 30 degrees less than the rest of the problem. Then if I use pressure-outlet I am overdimensioning the problet cause the specie mass fraction is fixed in the outlet. I want to fix the pressure at the outlet but I want fluent to compute the mass fraction of the specie at the outlet. It seems to me that BC overdimensionalize the problem and I don't fine the way to solve it. could anybody tell me something about this?

thanks in advance