Boundary condition
 

Suppose I were running an external plus internal aerodynamic flow simulation for an automobile, what boundary condition should I give for the windows? Considering that I would be studying the flow going through them and inside the automobile as well.

You can use interface. For example consider the car a region and the rest another region. Then the windows as interface boundary conditions.

The default option under Interface will do? Thank you!

Another small query. In case I need to switch between wall condition and interface i.e determine the aerodynamic effect of closing and opening windows on the body. How would the region splitting part work then?