Unfortunately, I am not a big fan of wind tunnels.
While one can scale the model, you cannot scale the air. There are a few full scale wing only tunnels I believe, but again, I have not seen results that match what has been measured in-flight.
I would also point to wake turbulence modelling. After over 40 years of trying, the model, transport, and generation has yet to be understood, nor able to be recreated in any form of modelling medium (wind tunnel, computer, etc)....
There is the never ending winglet/sharklet/xwing configuration issue. If the wing dynamics were understood, there would not be an issue.