Hope you got lots of money for this as this kind of technology doesn't come cheap.

Years ago I came across a book on windtunnel design. There was some interesting stuff but it soon showed my that I was out of my league pretty quickly.

The 25 cent explanation. Circular is best but square or rectangular with large corner fillets is not too bad either and it lends itself to a decent work area. To move the air you need a fan. The fan needs a powerful motor if you're moving much air at any sort of decent speed. I have no idea how much power you need but for single pass tunnels (open ended) it takes more power than for a closed loop. If you go for the loop idea you need a sets of airfoiled vanes in the corners to prevent turbulence. The wake off the impeller blades needs to be evened up and straightened. Sets of honey combs with the holes about 4 to 6 times as long as the hole diameter in a series were suggested for this. And for very low velocities with very little turbulence they even used a fabric barrier to help even up the airflow across the whole face of the tunnel and to eliminate the last of the turbulence from the honeycombs.

If you're looking for something to do airfoil testing then a fairly small tunnel would fill a good size room. If you need a test area larger than 3 feet x 3 feet x 5 feet then you'd better buy a large lot. You need that much room for the air to run around and settle before it hits' the test area.

You've certainly got my curiosity up. What are you planning on doing with this tunnel that you can afford the 100 grand or so to build it?