[GAUSSteam]

Hi all,
I have a problem simulating a exhaust plume of a rocket, in particular I need to simulate species diffusion without reaction. I am using a 2D axisymmetric domain with a gasinlet and a air inlet, for the gas inlet I put the mass fraction of species, with a pressure inlet, and for air (inlet) again a pressure inlet. top edge is a pressure farfield BC, and the outlet is pressure outlet, I am using a density based solver. A courant number of 0.25, and second order upwind. I am using ideal gas law for density, mixing law for Cp and mass weighted mixing law for thermal conducivity and viscosity. Kinethic theory for mass diffusivity and thermal diffusion coefficient. I tried different methods but I always get divergence in species residuals.

I don't know if the error is in wrong boundary conditions.
What should I try to change? I don't think the mesh is a problem since my domain is just a rectangle and I tried different meshes.

Thank you.