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I have a question regarding my wind tunnel design. Originally the system had a 90mm dc fan pulling air, upon testing I find the design unsatisfactory as air movement was very "weak" ( I used my hand to feel the air moving at the front end ). So I decided to replace it with a 140mm noctua ippc fan, an extra adapter had to be design to fit the new fan.

My question is how severe will air flow be affected by the sudden expansion at the end of the diffuser originally meant to mount a 90mm fan? I am also willing to start over with a new design if that's easier than fixing this. My design is based on this paper

Below are pictures of my design:

  1. Sideview of the wind tunnel, 140mm fan is represented as the box at the end of the wind tunnel, with the adapter preceding it. Missing walls at the testing chamber and diffuser will be covered with thin transparent plastic. enter image description here

2.Angled view of the wind tunnel enter image description here

3.Front view of the adapter, connected to diffuser enter image description here

4.Rear end of the diffuser, connected to 140mm fan

enter image description here

5.Cross-sectional view of the adapter, the angle of expansion was first decided at a constant 22.5 degrees then "smoothen out" enter image description here

Thanks for reading through all these, would appreciated any input.

Kevin Nan Woon Kai
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  • I think it depends on the output of the wind velocity/pressure of each fan can produce. – r13 Sep 23 '21 at 19:29
  • @r13 Thanks for your input, few month back I have ditched this idea and went for a rectangular wind tunnel instead, it gives me more space to work with things – Kevin Nan Woon Kai Sep 25 '21 at 10:41
  • I hope my message has come across that a more powerful larger fan does not necessarily produce a stronger wind than its smaller counterpart. The fact is simple, a floor fan can cool a room while a handheld mini fan can cool you effectively and faster, the speed and intensity are what that counts. A calculation of forced flow through varying areas can provides you with the answer you are seeking. – r13 Sep 25 '21 at 19:25
  • @r13 will look into that, a better fan is definitely needed to replace the current weak fan, thanks for the info – Kevin Nan Woon Kai Sep 27 '21 at 03:10

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Since you already have a complete model, I think the best way to determine that is by performing a CFD simulation and measuring the turbulence that is generated.

More specifically, I would try to change the angle of the diffuser and measure the effect of the turbulence where the air foil will be situated.

NMech
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NASA has A Java app for open wind tunnels that lets you change the parameters and see the difference. if you have not seen it already.

here is the link:Java app

kamran
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