OK. For the external boundaries (tunnel ends) you need pressure or velocity, the choice will depend on what you know.
For the ducts it's a little more complicated. Do you need to model flow in the duct, or do you just need to understand the effect of the duct flow on the larger tunnel? Have a look at fan boundary conditions and FIX cell zone conditions, or neglect the inside of the ducts and use velocity boundaries with +/- components to suit.
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