Introduction: How to Make a Wind Tunnel
Third Prize in the
Instructables Green Design Contest
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:
-Toilet Paper rolls/ Used paper towel rolls
-Sheet of Lexan (Might be a tad expensive but does not shatter when cutting with a jigsaw)
-Measuring tape/long straight edge
-Sand Paper/ Dremmel
-Hot Glue/ Waterproof adhesive
-90 degree angle tool
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
-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
-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.
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