[Eko]

Hey guys I need your help.

I am working on a natural convection case and am looking at a building with openings in the walls and ceiling.
The air in the building/room is heaten up by a heat source implemented via fvOptions. So far so good, this works fine.
The problem I have is that there is no transport between the air in my room and the air outside of it. Whether U or T seems to change.
I don't really know which boundary condition I should set for U at the coupled patches. (Air_to_Umgebung, Umgebung_to_Air)

    Air_to_Umgebung
    {
        type            compressible::turbulentTemperatureCoupledBaffleMixed;
        value           $internalField;
        Tnbr            T;
        kappaMethod     fluidThermo;
    }

Which boundary condition should I use for U?
Any help or tip is appreciated

Attached a small picture (colouring according to U)
Green=air room
Blue=air outside
Was using noSlip as boundary condition, don't ask me why :/
zeroGradient isn't working either (temperature blows up)