Science Buddies: "Ask an Expert"

Hello everyone,
my name is Andrea and for my High school final exam, I decided to build and bring to school a Wind Tunnel.
Looking around the web I found the Science Buddies's project about the Wind Tunnel really interesting and really well done; I so decided to base my project on this guide.
https://www.sciencebuddies.org/science- ... troduction
However, I have some questions and doubts that I hope some expert can answer to them.

1) Which is the SCALE, the Tunnel has been built with?

2) When I test in the Test Section "wing profiles or cars" (Miniatures), do they have to be with the same scale the Tunnel has been built with?

3) If I reduce the dimension of the Wind tunnel of half the size it's suppose to be built (the size the project makes you build), do I also have to reduce the Fan using one that is half the power?

Thanks all for the technical support.

Hi Andrea,

I should say that aeronautics and engineering are far from my areas of expertise. Perhaps one of the other experts will chime in and provide better answers to your questions.

There is a thread in this forum with questions and answers about the wind tunnel that you may find useful:

viewtopic.php?f=2&t=5002

I don't know the scale of the subsonic wind tunnel. The wind tunnel was designed to make lift and drag measurements on wing models. And I think that you can compare results for models of similar dimensions that fit within the test chamber of the tunnel. So it's probably more important to test models of the same scale than to match the scales of the models and the tunnel.

If you are making a smaller version of the wind tunnel, you might want to use a fan of lower flow capacity. A fan rated between 1600 and 2000 CFM (cubic feet per minute) is specified. The cross-sectional area of the test section is 1 square foot. So the wind speed produced by a 1600 CFM fan is 1600 feet/minute (or 18.2 mph). If you reduced the area of the test section to 0.5 square feet and used the same fan, the speed would double to 3200 feet/minute (or 36.4 mph). Using a fan rated at 800 CFM would produce the 1600 feet/minute speed with the 0.5 square foot area.

I hope this helps. Please ask again if you have more questions.

A. Norman