[kennybobby]

You may want to have two test chambers--one for small models in addition to the full scale testing.

The inside wall shape will need to be designed by you using aerodynamics just as in wing and foil design. The inside wall could be built like an airplane--structural frame covered by thin sheetmetal skin with countersunk rivets, etc.

The range of speeds you want to test will help determine how much energy and power you need. Determine the volume of the chamber and consider the weight/ mass of this much air moving at your speed as the base, then add the aero drag of the walls and of the test article. That will get you in the ballpark and will be quite large for full scale--that's why folks use small tunnels and models.