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5-Regular Member

## 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?
FLOW Q1?
VELOCITY V1?

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 in Mathcad file? or should it be done in Matlab script instead?

20. How can I obtain Inches of water in Mathcad?

Thank you

2 REPLIES 2
23-Emerald I
(To:jrodriguez-9)

Wind tunnel design is as much "black art" as science.  A short pass at a few of the simpler answers:

• Mass flow is conserved, not volume flow.  Air is compressible, density changes (not much, but it changes.)  So density times velocity times area is constant.
• You want as large a contraction ratio as you can accommodate.  The 10 m/sec should be the fastest air speed in your design.
• The dynamic pressure at the exit (density times velocity squared/2) plus the static pressure at the exit (one atmosphere?) is the total (or stagnation) pressure.  The fans need to be able to accommodate the mass flow required AND develop that pressure rise.
• The largest loss in your system will be the diffuser that "catches" and decelerates the air after your test section.  The loss in your contraction section will be small by comparison.

There are a number of books.  Low Speed Wind Tunnel Testing, Pope and Rae, might be a good place to start.  There are newer editions, an older one might have more "rules of thumb."

24-Ruby II
(To:jrodriguez-9)