Expert: Paul Soderman - 2/3/2012

Question
sir i,m willing to design and construct a wind tunnel so what are all the basic things needed to design. i need basic ideas and details to design to design wind tunnel. would u please help us.

Answer
Vinodh
I get many questions about wind tunnel design. Like any experimental facility, a wind tunnel design depends on the project requirements and objectives, which are unknown to me. So, I can only offer a generic answer as follows:

The type of research or testing to be accomplished is needed to estimate what turbulence and velocity distributions are required. If you don't need especially clean test-section flow you may not need any screens or honeycomb.  If the flow must be very clean, you may need several stages of flow treatment.  

You can find a discussion and guidelines for wind tunnel circuit design including contractions, screens, honeycomb designs, and diffusers in W. Rae and A. Pope:  Low-Speed Wind Tunnel Testing. Although the guidelines are pretty straightforward, the subject is too complex to get into here in detail.

An inlet and settling chamber and contraction are key components. The challenge for contraction design is that there are adverse pressure gradients at the entrance and exit.  Flow separation can occur. In addition, at the corner of rectangular contractions the boundary layer can get large. I offer the advice for a contraction shape from my friend and former NASA wind tunnel designer Ken Mort:

'The shape should be an S shape with cubics at each end. The inflection point should be much closer (1/4-1/3 of the length) to the inlet than the exit.  I like the guides given in the following.

Rouse, Hunter and Hassan, M. M.: "Cavitation-Free Inlets and Contractions". Mechanical Engineering, Vol. 71, March 1949, pp 213-216.

The same guides are also given in NASA TN D-8243.'

If you can get the following references, you can see what others have done with honeycomb and screens:

R. Loehrke and H. Nagib: Experiments on Management of Free-Stream Turbulence, AGARD Report 598, Sept 1972.

R. Loehrke and H. Nagib:  Control of Free-Stream Turbulence by Means of Honeycombs:  A Balance Between Suppression and Generation. J. Fluids Engineering, 342-353, Sept 1976.

If screens are required it would be good if you could remove the screens for cleaning because they tend to trap dust and change their performance.  If multiple screens are used they should be spaced 30 times the mesh size or 500 times the wire diameter, whichever is larger, according to Rae and Pope.

See Rae and Pope for design of diffusers, turning vanes, drive fans, etc. You can also find examples of existing wind tunnels that may be similar to what you need. Be aware that performance depends on flow Reynolds number so scaling a large facility to small scale might lead to problems. Good luck.
Paul