# How to Make a Wind Tunnel

205,553

358

59

## Introduction: How to Make a Wind Tunnel

It's always been cool to see the car commercials depicting the clean, crisp, curvature of cars (namely the Infiniti commercials).   As an aerospace/aerodynamics enthusiast, I spend my free time looking at planes and watching videos about how they work and interact with the medium they travel through, air.  For a while, I've known that planes, rockets, and even cars are designed by subjecting small scale models of them through an instrument known as a wind tunnel.  However, the wind tunnels I know of are either very big, expensive and hard to access unless you have connections or small pitiful demonstrations the science museums use show the airflow around a very limited array of  objects, often times a static display.  I've always desired to see the effects of different objects in wind tunnels for myself so when my physics teacher gave us a end-of-the-year assignment to learn about anything physics related and use what I've learned to teach the class, I thought to myself, this is a perfect moment to make a wind tunnel.  I partnered up with a peer, Ian Kelley (also interested in testing out various objects and seeing their effects) and we set out to build a wind tunnel that was simple and cool at the same time that we would be able to see the effects of air clearly on various objects.   This is a guide documenting our process and how the problem was approached.  Included are images and tips on how to make your very own tunnel cheaply in order to learn about the aerodynamic properties of objects. Hope you enjoy.
UPDATE: Be sure to check out the updated version of this project, here.

## Step 1: Design & Why?

To start off, we knew the basics of wind tunnel.  A air source that is compressed, increasing the speed allowing for various objects to be tested for aerodynamics and air resistance. A source of inspration for making the tunnel was another Instructable that was made previously by user Goalieguy (https://www.instructables.com/id/Cardboard-Wind-Tunnel/ be sure to check it out!).
We also used NASA as a resource into the design of the tunnel.

Now that the tunnel design was set, we had to come up with a way to generate smoke.  Ian thought up of the idea of using a pump and a jar and that can be seen on the bottom right side of the diagram.  Pretty smart idea I gotta say.

Now how does a wind tunnel work? Well the physics behind it are based off the work of Daniel Bernoulli, a Swiss physicist.  Many might remember him from the equation that you learned in physics back in high school of constant= P + 1/2 p v^2 + p g h.  An equation he helped contribute to, the continuity expression in physics of A1V1=A2V2.  This provides the foundation of wind tunnels by showing how if you decrease the cross sectional area, your  speed subsequently increases.  In the case of this specific tunnel that was made, the speed increased by a factor of 3.5 from leaving the fan to being compressed by the contraction section.

## Step 2: Stuff Needed to Build It and Make It Happen

In order to make the wind tunnel, you need the following materials and tools:

~Materials
-Cardboard
-Toilet Paper rolls/ Used paper towel rolls
-Sheet of Lexan (Might be a tad expensive but does not shatter when cutting with a jigsaw)
-Fan
-Duct Tape

~Tools
-Hobby Knife
-Scissor
-JigSaw
-Ruler
-Measuring tape/long straight edge
-Pen/Pencil
-Sand Paper/ Dremmel
-90 degree angle tool
-Gloves
-Safety Glasses

These two lists are purely to make the tunnel itself without the smoke section to make the airflow visible.  Keep in mind that some of these materials and tools are optional and not necessary to complete the project.

## Step 3: Make the Contraction Section

Now it is time to make the part of the tunnel that helps magnify the force of the wind by using Bernoulli's principle to increase the speed of the air that is being pumped from the fan.

Refer to diagram in step 1 on how to properly tape the pieces together.  Remember to tape in the inside and outside to have a smooth transition between two pieces and to reinforce the part.

## Step 4: Making the Flow Straightener

Gather around 20-30 tubes and arrange them in such a way that the outer ones are the largest and the inner ones the smaller ones.  Tape this arrangement together and place into the three sides of the body of the tunnel.  Once you squeezed all of the tubes inside the tunnel, tape on the 4th side and bam you are done!

## Step 5: Testing Section / Exhaust

This section can be of any length, enough to incorporate your flow straighter, the hole for the gas intake, and viewing screen.

For this section, what we did was cut out 3 parts of the 4 and for the 4th part, use a shorter piece cut that in half and have the Lexan sheet in the middle of the two. Don't forget to peel off both sides of the Lexan protector!

The last two images show how to make one of the two stands used to stand the tunnel up since it is at an angle without this part because of the contraction section.  Just cut slots into each piece and shove them together to make the stands.

## Step 6: Smoke Generator (Important Tips Included)

This step is essential to the tunnel since you need some kind of indicator to be able to see the approximate wind flow. As to what the smoke is out of, we first tried using incense for the smoke.  This was a horrible idea since we were stuck testing with this in a dark, closed garage with airflow from a fan for 3 hours.  Incense also clogs up the tubing over time and we constantly had to clear the tubing and reignite the incense if it ran out.  The single most important tip I would give is to use dry ice and warm water if you have access to it.  The purpose of the water is to speed up the process of creating smoke since the cooler the temperature of the system, the less likely the ice wants to sublimate into CO2 gas.  It is also cleaner and doesn't clog up the tubing as much.  Only downside is that you need a water catcher under the tubing when the cold air condenses inside the tubing creating water.
The first image is what you want to make.  Refer to the bottom right corner of the design diagram on step 1 for details.

Basically, you will need the following to make this
~Materials
-Jar w/ lid
-Hand pump of some kind
-1+ ft of Airline tubing (fish tank)
-Hot Glue/ Water tight sealant
-Incense / Dry Ice + warm water

~Tools
-Drill w/ right bit for the tubing and pump head to fit into

WARNING: NO MATTER WHICH WAY YOU DECIDE TO GO, PROCEED WITH CAUTION AND AT YOUR OWN RISK.  IF USING INCENSE BE SURE TO AERATE THE ROOM AND BREATHE IN AS LITTLE OF THE SMOKE AS POSSIBLE.  IF USING DRY ICE, BE SURE TO WEAR GLOVES AND HANDLE WITH CARE SINCE IT CAN STICK TO SKIN WITH DIRECT CONTACT AND CAUSE SEVERE INJURY.  DO NOT BREATHE THE GAS FROM THE ICE SINCE IT IS CARBON DIOXIDE AND YOU NEED OXYGEN TO LIVE.

## Step 7: Final Touches

This makes everything stand out and look nicer and stand out especially those that are far from the tiny viewing screen.  Attach a string of Christmas lights into the tunnel.  Since they were a pretty long sting, we tried putting one part at the top and weaving it back around the bottom.  It looks great but has a reflection when taking images to we just opted to stay with the lights at top.

Next, adding a back background to your testing section helps give a good contrast to the smoke/gas and helps with viewing the thin wisps of smoke if you happen to be using that.

Lastly, in order to splay the tubing ends, you get a pair of scissors, put into the tube about 3/4'' and cut that multiple times around the tube to achieve the effect.

## Step 8: Experiment!

These are pictures of things I used to test and what it looked like with the fan on and the smoke blowing.  I did this testing with smoke, which did not look as good as dry ice + water but I did not get pictures of those.  Try out different things and see what effects you get with them. Personally, I thought the paint scraper sponge was the coolest since it was porous and it curved the smoke upwards slightly.

Post your tests below in the comments!  I can't wait to see what others have to try!

## Step 9: Finale

I would like to thank Ian Kelley for helping me with this project and Mrs. Hester for allowing us to bring it to school and teach kids about how wind tunnel testing affects the designs of everyday modes of transportation.

Thanks for viewing this Instructable!

Third Prize in the
Instructables Green Design Contest

Participated in the
Epilog Challenge V

Participated in the
Craft Contest

72 6.3K
6 1.6K
29 3.2K
48 7.0K

## 59 Discussions

What size is the sheet of Lexan?

hey you got a good thing done over there
great wind tunnel.congrats
i just have a tip that incense stick need not be used with a tube
in my wind tunnel i used incense and kept it in front of the fen like another tweeny bit of section seperated for smoke from incense

Hello. I am planning to build and control a wind tunnel for my final year project. I am interested in your design and would like to design a similar one. Do you have an operating video?

I think every school should have a wind tunnel. I have built a simple one for our school, and it is immensely popular!

what grade are you in? there are thousands of experiments all schools should have.

whats the use of sand paper in this project

I liked this project very very much. I wanted a project for my science exhibition and I have got it. thanks.

I wish you the best of luck with your science exhibition project. I'm sure you can make your wind tunnel even better than mine by integrating some sensors! :)

Very NIce.
Now I have a headache. I want to build a wind tunnel to test my VAWT. 24"x24". My question is Scaling. How much larger should the test section be than the object being tested? With that I think I can figure out the math for the rest of the tunnel.

Thanks,
AAron

The rule of thumb is that the frontal area of the model seen by the flow should be less than 7.5% of the cross-sectional area of the test section. So if you want to test a full size VAWT you will need a very large wind tunnel. It would be more practical to test a scale model and relate the model results to the full scale prototype using similitude and pi groups.

I am not sure exactly of how large you should make it, my guess is that you should just make it big enough to be able to fit the test subject into the tunnel with enough clearance for instruments and taking in and out. As a high schooler, I am still limited on my knowledge of aerodynamics since they do not teach this stuff at school. You might have a better answer if you ask one of these professionals on this incredible website. Thanks. :)

Thank you James. I do love the avatar.

High School? That is AWSUME!! You can think and learn own you own!

Much respect to you!

I found some where, (1' item = 2' test area) 2x size larger than the item being tested.

Thank you, AAron

I think Coroplast (corrugated plastic, the stuff election candidate signs are made out of) would be a great material for a flow straightener.

That is a good idea to use!
I wish I thought of that before I cut all my straws for my new tunnel... haha
Thanks for the suggestion. :)

For airflow straightener you might want to Google "Laminar Flow" but straws seem to be the most common things used for this scale.

If you mount your model on a scale you can measure lift (or downforce). Many supermarkets or electric stores sell cheap digital scales with accuracy of 0.1 oz or 1 grams. Mounting another scale behind the model and use a lever to convert horizontal force to vertical force will give you the drag of the model. The scales will not be accurate without calibration but will be good indication and are very useful for comparison between objects.

For my new wind tunnel, I used an array of straws to straighten the air. As for the scale, I looked into measuring the amount of drag in the tunnel but found that to be over my \$100 budget. If I obtain the resources and time to keep adding and improving to the tunnel, I will look into this because I also encountered a professional at MakerFaire that commented on doing this. Thank you.

Great little project.

I am going to try to build a couple myself - hopefully one large enough to take a bicycle.

I'm in Asia though and it can be difficult to get some things here.

For a larger one, say around 1.5mx1.5m for the main tunnel section, what would be the preferred diameter of the flow straighteners? I'm thinking about using some kind of plastic sheathing used for fluorescent tube bulbs or something similar, probably 1 inch in diameter or so and around 10 inches in length. I'd probably build a set of 4 fans attached to a plywood board.

Would I need to have additional fans on the intake side to keep the air moving? I was thinking about using several smaller fans just to increase airflow, but the more I think about it, the more I am questioning whether they would be helpful.

I am thinking about putting a set of fluorescent tubes at the top with a half foot recess and straight edges to make some directional light from the top, with black velvet at the back of the viewing area. That should light up the smoke. Maybe need some lights on the bottom too.

Thoughts?

Build Your Own Inexpensive Wind Tunnel