[Marcel95]

Dear CFD Users,

i am working on a freejet simulation with StarCCM+.

Because the freejet consists of hydrogen and the ambient gas is air, the jet will be especially further downstream buoyancy dominated. I think this buoyancy makes some problems in this case, because with gravitation deactivated (and therefore no buoyancy) the fluctuations do not appear.

Simulation Details:

- steady
- multicomponent Gas (H2 and Air)
- non reacting

BC:
Inlet (bottom of the picture, the beginning of the tube): Velocity Inlet with species condition 100% Hydrogen
Walls (left and right side in the picture): Wall with species condition: 100% Air
Outlet (Top of the picture): Pressure Outlet with ambient pressure and species condition 100% air

Problem: At some area the jet has heavy fluctuations, i attatch a picture of the Mole Fraction of H2 after 1000 iterations

I attach a picture of the residuals plot as well.

Someone any idea how to solve this Problem? I want to validate my CFD result later with experimental data, so it would be perfect to get a smooth, steady result to do that.

Thanks for your help!