Here is my NACA0012 project, it’s my playground for trying weird things so excuse the mess. The best example is validationMK2, to get an idea of setup (ignore the failed runs 
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But essentially the walls above, bellow, upwind and downwind are set to inlet-outlets, where they don’t ‘know’ about what lies outside them (such as surrounds or wind tunnels) they ‘know’ that air is travelling in a direction that is going into the domain, if flow exits the domain, then it acts as if it just moves out of it, to us that is zero gradient. So there will be no deflection from any wall external to it, nor will the walls themselves make the flow behave any differently to if they were orientated with the flow.