Building the Tunnel Structure
The idea is pretty simple and the exact dimensions are not critical. You need a box fan, some cardboard boxes and a sheet of thin clear plastic. The core of the tunnel is about a foot square, which can be made from one box. Another, larger box is modified to flare from the tunnel section to the size of the fan. The actual dimensions will be dependent on the size of the boxes you have available. The length of the straight tunnel section should be at least three or four times the width of the tunnel. The tunnel in these photos is a foot square and the straight section is 38 inches long. We tried various features and made modifications along the way as we learned what worked best.
Cut a window in the side so you can see the test article in the middle of the tunnel. For this, we used an inexpensive document frame that had a plastic cover. The original window was just taped on. During the rework, we added some cardboard slots so the window could slide out for better access to the test article.
We made a grid using large diameter soda straws (see photos below). This grid only needs to be one to two inches long. Pieces of the straws are stacked and glued together. Note that the grid is a separate unit that can easily be removed. A tight rectangular grid made of thin cardboard would also be effective.
Links:
Summary
Part 2 - Test Section
Part 3 - Lesson Plans