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Old Jun 8th 2018, 01:46 PM   #1
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Vertical Wind Tunnel and Selection of Fan(s)

Hi, I will like to design this vertical wind tunnel (large nozzle) to shoot air out at 10 m/sec at the exit and a diameter of 8 ft.
However I want to understand the following parameters. Does anyone know about this? and know how to calculate the following parameters ?:

We want V2=10m/sec (outlet velocity at jet)

I want to design a fan or number of fans arranged (or framed together) that can do the job and how can these fans be selected?

1. Does the contraction ratio (Alarge/Asmall or Ainlet/Aoutlet) should be kept at 8 only from a square to circular contraction? or can any contraction ratio should be used?
2. Does the continuity equation applies? Can you find the total required flow rate Q1 if you have V2=10 m/sec? Can you use: Q1=Q2 thus Q1=A2*V2?
3. How do you find the total loss?
4. How do you find the dynamic head (both at inlet and outlet)?
5. How do you find the static head (both at inlet and outlet)?
6. How do you find the total pressure head?
7. How do you find the total power required (horsepower)?
8. How do you find the "Backpressure of the system?
9. How do you find the pressure being pushed through the exit cone?
10. How do you find the total pressure in inches of water?
11. How do you select a fan? what parameters do you need?
12. How do you select a complete multiple fan assembly?
13. Can I place several fans in a rectangular matric at the inlet or can they be placed circular? what is the best way?
14. What is the best material to build this of? (aluminum, steel or plywood?) what thickness is ideal?
15. What is a good physical closing-opening mechanism at the outlet?
16. How can a frame be designed to hold something like this?
17. Can all these parameters be obtained from an Ansys v19 simulation?
18. How can this be developed simple in Ansys 19 fluent if I have the CAD file?
19. How can I develop a Matlab script for something like this?

Thank you
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Old Jun 10th 2018, 08:39 AM   #2
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The answers to your questions are unlikely to be available in a forum like this,
Wind-tunnel design is a specialist subject.
I don't believe the maths is hugely complicated, but there are a large number of mutually interacting factors.
I just did a quick Google on "wind-tunnel design" and was quickly directed to an number of pdf downloads.
I would suggest studying these.
If you have some specific queries arising from these studies, then we may be able to help.
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Old Jun 10th 2018, 07:16 PM   #3
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The way to approach this is to see what other people have done ....

This is about 8 feet diam , it's for people to fly in , so the velocity will be much greater than you require ....Are you sure you want 8 feet dia....??? and your velocity is quite low ...

The biggest challenge is getting a smooth non turbulent flow .... so it's not a good idea to have a fan pushing air through the orifice in your sketch ....

If i were doing this I'd look at a fan like this ....

Only $3 including delivery (eBay) 12 cm square .... it will give the sort of air velocity you are looking for , backpressure in your wind tunnel will be small ....

Buy one of these to check out the air speed , if looks promising then 4 hundred of these joined together (in parallel) will push a smooth air flow over the area you require , you will probably also need a grid of baffles through which the air flows to get a perfectly smooth flow ...

you can also build up slowly , perhaps buy 16 , build a 4x4 tunnel (half a meter by half a meter) ... flow is easily adjusted by changing the voltage

One fan is 3.6W ...you will need about 400 for 8 foot square.... less than $1000 ..... 1.44Kw .....that sounds about the sort of power you will need ....
Also you will probably not need a frame for these fans , tied together at the corners with wire through the small fixing hole , they should form a fairly solid matrix ..
Going the other route of one , or a few big fans will be more expensive , consume more power and make a very turbulent flow ...

Last edited by oz93666; Jun 10th 2018 at 07:25 PM.
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