So who here has tried to make a homemade wind tunnel? My first attempt

In summary, the conversation revolves around building a wind tunnel using an 18" centrifugal fan. The original poster is a hobbyist who wants to use the tunnel for testing small winglets for downforce on cars. The fan is powerful, reaching above 2000rpm with 14 horsepower, but concerns are raised about safety and controlling the airflow. The idea of using a honeycomb to straighten out the airflow is suggested, and there is discussion about the best way to measure and control the airflow in the tunnel. Some suggestions include using a water manometer and a digital scale. A website with a similar setup is shared, and there is talk about using a pusher fan instead of a puller fan to achieve smoother airflow in the
  • #1
kazx9r
49
4
Hello all, i posted this on another forum but didn't get much response, I had an 18” centrifugal fan around around and wanted to see if I can push some real air to make a wind tunnel. I'm just a hobbyist, and like to build and modify cars, figured this would be something to look into.

Looks like this:
192622.jpg


Trust me this thing is heavy and pretty big but is it big enough?

Spec picture Shown here page 107
fandimensions.jpg
18-13a, so 18 diameter with about a 18”x18” outlet.

fanhp.jpg

Chart only goes to 723rpm but I got this up to just above 2000rpm, took 14Hp, I may add some more motors.
Excuse the mess just a test run for 2 minutes just a 12 second clip:



Crazy right? This thing really blows some air, my guess 50-70mph (need a wind meter) my plan is to test small winglets for downforce.
My question is the honeycomb, is it needed? Amazon has a few but they're 1/4" holes but only 1", i need probably around 3-6" for a honeycomb? any thoughts.

I would greatly appreciate if someone could share their experiences or critique this project.
 
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  • #2
The honeycomb can be made from short thin-wall tube sections, cut from pipe, then glued side by side in a hexagonal pattern. Select the material and tube size you need. You may be able to throw out many redundant elements from the array where there are double walls not needed for structure.
 
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  • #3
Baluncore said:
The honeycomb can be made from short thin-wall tube sections, cut from pipe, then glued side by side in a hexagonal pattern. Select the material and tube size you need. You may be able to throw out many redundant elements from the array where there are double walls not needed for structure.
would this work?
honey.jpg


https://www.amazon.com/dp/B01AYIZ5MK/?tag=pfamazon01-20
 
  • #4
The manufacturer's maximum rating for that blower is 3 HP. I wouldn't let anyone that I love stand anywhere near it at 14 HP.
 
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  • #5
I hear you Dullard, i told them to stand back. Haha. Thing is heavy, I over built it, 1.75" solid steel shaft almost 26" in length, pillow block balls bearings, but still need to reinforce it, the cage is not that sturdy.
 
  • #6
kazx9r said:
would this work?
That will depend on the length and geometry of the airflow, how much untwisting is needed, and how much variation in velocity across the section can you tolerate? Will you close the airflow cycle?
 
  • #7
Baluncore said:
That will depend on the length and geometry of the airflow, how much untwisting is needed, and how much variation in velocity across the section can you tolerate? Will you close the airflow cycle?
Thank you

It’s pretty turbulent coming out of the fan, I don’t think I have the space to close it.

What are you thinking for measurements? I saw a few videos where people put the wing on vertical sliders, I was thinking of doing that but have calibrated springs to measure sure the distance moved. f=kx b but open to any idea.

And then for drag using the sliders but horizontally, just thinking out loud.
 
  • #8
kazx9r said:
It’s pretty turbulent coming out of the fan, I don’t think I have the space to close it.
Then you may as well give up now.
You must control it, or measurements will be unrepeatable noise.

kazx9r said:
What are you thinking for measurements?
I would measure pressures with a diagonal water manometer, and weigh the forces with a digital scale.
 
  • #9
Baluncore said:
Then you may as well give up now.
You must control it, or measurements will be unrepeatable noise.I would measure pressures with a diagonal water manometer, and weigh the forces with a digital scale.
Thank you, by closed do you mean closed loop or build the contraction, chamber and diffuser? Of course I plan to do this but do I need to have a closed loop?


As for instrumentation, I’ll take a look at the manometer.
 
  • #10
kazx9r said:
Thank you, by closed do you mean closed loop or build the contraction, chamber and diffuser? Of course I plan to do this but do I need to have a closed loop?
There are two possibilities: You could get out of the wind by shutting yourself in a fixed position, closed box, or you could control the circulating air by enclosing that in a box.

You need to keep your body from disturbing the returning airflow. Until you close the tunnel, your body is part of the experiment.
 
  • #11
Baluncore said:
There are two possibilities: You could get out of the wind by shutting yourself in a fixed position, closed box, or you could control the circulating air by enclosing that in a box.

You need to keep your body from disturbing the returning airflow. Until you close the tunnel, your body is part of the experiment.
balan, thank you

Someone posted this,

https://www.frh.utn.edu.ar/media/empresa/laboratorios/03_LA_fluidosytunel.pdf

is this what you have in mind? This looks similar to what I had in mind. So in order Fan, contraction, honeycomb, test chamber and then diffuser.
 
  • #12
kazx9r said:
Someone posted this,
My Spanish class was decades ago. Maybe you could provide a translation of any part that confuses you?

Also, I don't know if this has been mentioned already (sorry for skimming you thread), but you can achieve a lot smoother airflow in your test section of the wind tunnel by using your DIY air pump at the outlet, instead of trying to use it as a very turbulent pusher at the inlet...
 
  • #13
berkeman said:
My Spanish class was decades ago. Maybe you could provide a translation of any part that confuses you?

Also, I don't know if this has been mentioned already (sorry for skimming you thread), but you can achieve a lot smoother airflow in your test section of the wind tunnel by using your DIY air pump at the outlet, instead of trying to use it as a very turbulent pusher at the inlet...
Thank you, I have no idea what the pdf says I meant the setup they had in it
D6DCACAB-66A8-47D4-95AA-7046F035191E.jpeg

That looks like a pusher fan so I’m going with a similar setup so we need to straighten out this airflow, I don’t think I can go with a puller setup. I have seen other setups with similar setups but I understand the pusher will take a larger fan but I think I have the size and power to achieve this part. Some other setups
01C9F3E8-C566-4AFA-8D61-B08B96A3EC36.jpeg

The above used straws for honeycomb.

Differences:
200E71F4-FB57-492C-91C0-803F82073E75.jpeg
 
  • #14
Stepping back for a second, I’m hoping someone can school me this, I understand for a lift and drag experiment the flow should be smooth and consistent however my setup is a downforce and drag experiment of a car wing or other car wing parts, I’m not trying to check airflow or vacuum under a car, only on top of a wing, a if I stuck a big ugly wing on my car with a strain gauge under it, and drive the car at say 70mph, would I never get a consistent strain gauge reading due to too much turbulent air?

It’s not like I can ask the flowing air to smooth out for me so I can get a reading.

Isn’t a turbulent air in a closed chamber a more realistic experiment than spending all this time trying smooth out the air with honeycombs and perforated sheets of metal.
 
  • #15
kazx9r said:
I hear you Dullard, i told them to stand back. Haha. Thing is heavy, I over built it, 1.75" solid steel shaft almost 26" in length, pillow block balls bearings, but still need to reinforce it, the cage is not that sturdy.
He’s probably more concerned about the fan blades failing from spinning it a 3 times the rated rpm. The applied forces on them should increase as ##F \propto v^2## in each principal direction( radially, and tangentially)?
 
Last edited:
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  • #16
kazx9r said:
is this what you have in mind?
I think that system is a first approximation to an open system. I would enclose the system in two distinct counter-flow channels.

You are working at low speed, well below the speed of sound, where air is assumed not compressible. Anything you do downstream will be reflected, to contaminate your test space. The test space needs a smooth flow without turbulence.

Put the test chamber in a restricted section of the front channel, with orderly contraction, collimators, and then orderly expansion.

Put the fan in the return flow channel where there can be some vibration isolation, noise and turbulence reduction.

Turning the corners between the two channels or ducts, with internal curved sheet guides in the bends, will be calming, and easier than designing and building an inlet horn for smooth flow, then working in the wind.

Start with several standard sized cardboard boxes, and discover why it is called "duct tape".
 
  • #17
erobz said:
He’s probably more concerned about the fan blades failing from spinning it a 3 times the rated rpm. The applied forces on them should increase as ##F \propto v^2## in each principal direction( radially, and tangentially)?
I get the thing about the safety and pushing this thing too fast, it needs to be checked for any blade damage or bending and also put some safety mesh.

thank you.
 
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  • #18
Baluncore said:
I think that system is a first approximation to an open system. I would enclose the system in two distinct counter-flow channels.

You are working at low speed, well below the speed of sound, where air is assumed not compressible. Anything you do downstream will be reflected, to contaminate your test space. The test space needs a smooth flow without turbulence.

Put the test chamber in a restricted section of the front channel, with orderly contraction, collimators, and then orderly expansion.

Put the fan in the return flow channel where there can be some vibration isolation, noise and turbulence reduction.

Turning the corners between the two channels or ducts, with internal curved sheet guides in the bends, will be calming, and easier than designing and building an inlet horn for smooth flow, then working in the wind.

Start with several standard sized cardboard boxes, and discover why it is called "duct tape".
thank you, I’m having a hard time visualizing this, any sketches of this setup online that you can link? All very interesting, thanks.
 
  • #19
Normally, we are skittish about dangerous topics here on PF. You're lucky this thread has been allowed to continue.

May I suggest wood as an effective and inexpensive shield around that overspeeded fan. 4x4 beams, or old railroad ties, or sections of tree trunk, might do the job. Hardwood (not pine) is good at absorbing the energy of impacting objects.

When I worked at General Electric, we had a turbine overspeed test stand. It was shielded by steel plate, plus 6 feet (2 m) of railroad ties in all directions. One day, a blade broke off the turbine being tested. It penetrated the shield and the roof of the building, went high in the air, then came down through the roof again several hundred meters away and killed an engineer who was sitting at his desk.
 
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  • #20
anorlunda said:
Normally, we are skittish about dangerous topics here on PF. You're lucky this thread has been allowed to continue.

May I suggest wood as an effective and inexpensive shield around that overspeeded fan. 4x4 beams, or old railroad ties, or sections of tree trunk, might do the job well. Hardwood (not pine) is good at absorbing the energy of impacting objects.

When I worked at General Electric, we had a turbine overspeed test stand. It was shielded by steel plate, plus 6 feet (2 m) of railroad ties in all directions. One day, a blade broke off the turbine being tested. It penetrated the shield and the roof of the building, went high in the air, then came down through the roof again several hundred meters away and killed an engineer who was sitting at his desk.
Thank you, that’s the next step. Putting mesh and shielding.

If the mods don’t like it then I have no issue with them deleting it. Forum is pretty dead except for Balun helping out.
 
  • #21
anorlunda said:
You're lucky this thread has been allowed to continue.
Yeah, good point. I hadn't been checking this thread very closely, and just now realized it's based on an overspeed blower. That's not a good design.

Thread is closed on that basis.
 

Related to So who here has tried to make a homemade wind tunnel? My first attempt

1. What materials do I need to make a homemade wind tunnel?

To make a homemade wind tunnel, you will need a large cardboard box, a fan, a plastic sheet or clear plastic wrap, scissors, tape, and markers for labeling.

2. How do I set up the wind tunnel?

First, cut a rectangular opening on one side of the cardboard box. Then, attach the fan to the opening using tape. Cover the other side of the box with the plastic sheet or wrap, making sure it is tightly secured. Finally, label the top and bottom of the tunnel for airflow direction.

3. What should I use as the test object in the wind tunnel?

You can use various objects such as paper airplanes, small toy cars, or even household items like feathers or cotton balls to test in the wind tunnel. Be creative and have fun experimenting with different objects!

4. How do I measure the wind speed in the tunnel?

You can use an anemometer or make a simple one using a small plastic cup attached to a stick. Place the anemometer in the tunnel and record the wind speed in miles per hour (mph) or meters per second (m/s).

5. What can I learn from making a homemade wind tunnel?

Making a homemade wind tunnel can teach you about aerodynamics, air pressure, and how different objects behave in different wind speeds. It is a fun and interactive way to learn about science and engineering principles.

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