Need help building a wind tunnel

[arthurleung]

I'm starting a project for my AH Physics. Planning to build a wind tunnel, but wondering what kind of fan should I use to power the wind tunnel? Going to test some aerofoil in it so I'll probably need 5~15m/s going thru the tunnel.

Thinking of fitting may be 8 high speed delta 12cm fans but I'm wondering if they can push enough air through the tunnel to get that kind of wind speed? The tunnel size will be about 31*x cm (where x = 10~31). Those high speed fans cost a lot though So I'm looking for alternative solutions or fans to do the job. Could be an industrial fan or computer case fans. Either running on 12V or mains is fine. But I need a speed control to adjust the wind speed. Thanks everyone

[mmh]

i have an industrial type fan that i use for band usage... it has a controller, but only a 3 step controller, i bought it from currys for £30 i think. its 18" which is alot bigger than u need, but if you make a cone to the size you want, the wind pressure will build up more inside the wind tunnel... maybe too much for what u need though.
Its mains controlled btw... reply to me if you want more info... MMH

[Theo]

If you have any more details about what sort of air movement you'll need I might be able to help

[arthurleung]

I just need a simple wind tunnel with an aerofoil inside to measure lift and drag. Thanks mmh I'll have a look in currys. Hopefully the air pressure will be enough. Coz theoretically a delta 12cm screamer fan will put out roughly 1.1m/s according to my calc.

[Theo]

A TD160 can be had for around £45-60. I'd imagine that a proper ventilation fan would be more up your alley?

[chrestomanci]

Seriously, you will have to do some calculations to work out what you need. You said that you need the air to move at 5-15 m/s, so from and the cross sectional area of the tunnel, that you should be able to work out how much air your fans need to move each minute, and choose appropriately.

I have just done some quick calculations, and I have worked out that if your tunnel is 30cm square, then to move the air at 15 m/s you need to move 1.35 cubic metres per second, or 81 per minute, which is about 2850 cfm. Even if those 8 high speed delta 12cm fans are working at perfect efficiency, I doubt they can each move air at 357 cfm.

Anyway, those are ballpark figures, you need to go away and do some maths, and work out for the size of your wind tunnel design.

Also, I would not assume that your fans will work at better than half their ideal performance, so I would put in more fans than needed, and use a flow meter to measure the air speed, and a rheostat to adjust the fan so as to get the correct speed for you experiment.

Also remember that the air coming of a fan will be quite turbulent, and will contain lots of eddies etc that will interfere with your aerofoil design. To get a laminar flow, you will need to pass the air though a honeycomb like mesh, to get all the air moving smoothly, and in the same direction.