[syble]

Hello,

My simulation is of a CO2-air variable composition mixture through a geometry. The geometry has an inlet (with a specific velocity profile and CO2 mass fraction) and an opening with a zero relative pressure. I would like to set a Neumann boundary condition (for CO2 mass fraction) on the opening boundary. Ie that the spatial gradient of CO2 mass fraction is zero on this opening boundary (since I do not know what the CO2 mass fraction at this boundary is but there should be no flux/rate of change of CO2 at the boundary).

However the only option in CFX pre is to specify the exact mass fraction.

Is there a way of having a Neumann boundary condition on this opening?

Thanks in advance for your help.