# Low speed wind tunnel - design and fabrication

1. Jun 22, 2009

### josh.k

Hello,

I'm a senior year ME undergraduate and I'm building a low speed (velocity=30-45 m/s) wind tunnel for my college as a final year project.

The initial size for the tunnel was 300mm x 300mm in the test section with an open circuit configuration.

I've read some papers on the design of a wind tunnel's components such as Design Rules for Small Low Speed Wind Tunnels - Bradshaw and Mehta, among others and I have some questions:

1. What is the difference, besides the obvious, between a 2D and a 3D tunnel? If size is a factor, what is the minimum test section size for a 3D tunnel?

2. For the wall profile of the contraction, if a defining equation is used, why is it necessary to have its second derivative zero at the two ends?

3. For the square contraction (area ratio 8 -12), if the equation for the wall profile is known, what method could be used to fabricate it out of sheet metal?

(I used NX sheet metal to develop one of the walls after i modeled it with a transformation of Bell and Mehta's curve, so that I could see its shape when unformed, if that could help, but I don't know what needs to be done after that)

Also, papers that have a lot of information about the performance and design wind tunnel components mostly have to purchased from their publications. Is there a source where these materials can be obtained freely?

If I have left out any relevant information, please let me know.

Thank you.

2. Jul 14, 2009

### Nick Bruno

This advice may be a little late, but I suggest you do not build a wind tunnel for a project. I did something similar and it is too sensitive and there are too many parameters to consider.

A lot of the time, it is good to normalize or scale down ur wind tunnel for calculations. Were you looking for laminar or turbulent flow? The longer your wind tunnel is, the more developed your flow will become.

You could use straws or flow straighteners... but since you are using sheet metal, i assume you are riveting it together. These rivets will effect your flow near the walls.

You would need a real long wind tunnel also if ur inlet is 30 cm to get a fully developed flow. Check it w/ a pitot tube.

3. Jul 15, 2009

### Cyrus

You should get a copy of low speed wind tunnel testing by Pope & Barlow.

Barlow is a good guy, and his book is well written.