free-slip walls with vicous fluid
 

I try to model the inviscid flow of air in the domain with heat addition. I use the 'Air' as the perfect gas of CFX. and I set the boundary condition of the walls as 'free slip' wall. By the effect of heat source in the domain, the temperaure of the air finally increase about 15 Kelvin.

I was wondering if this is the inviscid flow? I think not, 'cause the viscosity of 'Air' in CFX is not zero. So there's still the viscosity appear in the governing equations. Then what kind of flow do I have now?

I ask this because I try to do the dimensional analysis between the 'big' and 'small' models in CFX. I found the 10% discrepancy between these models. So I suspect that if this is the effect of viscosity in the flow, but how? because there was no friction loss between the flow and the walls.

Thank you for your consideration.