Re-used Parts Wind Tunnel

A wind tunnel made with cardboard and a Lasko box fan -- my sister came from summer camp with fan she didn't want and wasn't going to use. So, as one does, I made a wind tunnel.

Each step is structured in the following manner:

[

1) step 1

2) step 2... (these should be read)

More paragraphized steps + justifications + other information. (these don't have to be read)

]

Cardboard

Box fan

tape/glue

straws

paper, lego (or anything you would like to use to test)

small kitchen scale

1) Research online about wind tunnels. Great resources are NASA, other instructables, and wikipedia.

2) Consider resources, like what you can use, have access to, or need to buy. Also consider how much effort and time you want to put into your project.

3) Design it! (using the theory you have learned and your consideration of your constraints). You can take designs from the internet (like from here), modify them, or make your own!

Most wind tunnels are composed of a few main sections/components. 1) intake, 2) straightener, 3) test section, 4) diffuser, 5) fan They have a fan pulling air from the back (after the diffuser) for smoother flow. However, due to a lack of materials, my design had to be modified.

My final design, as shown, was 1) fan, 2) contraction area, 3) flow straigtener, 4) test section.

Firstly, as I lacked a clear material like lexan to have direct viewing access to the test section. So, I had to make a design where the test section was directly accessible. This forced me to remove my diffuser and move my fan to the front. While both are usually important, they were less so than the flow straightener. Additionally, because the straws I used were long compared to their diameters, the flow smoothness issue from moving the fan would be mostly mitigated.

1) Made 17 sheets of 17 straws each taped together. Used books to keep sheet sizes and dimensions consistent. Count carefully.

2) Layered sheets on top of each other. Used tape to put all sheets together for a 17 by 17 grid. Used their natural grooves to build them in a left-right-left-right pattern. This does result in the straightener being shorter than it is wide.

3) Measured dimensions of ordered straw bundle.

4) Used these measurements to make the cardboard test section that would be directly attached to it. The cardboard section should fit snugly around the straws without squashing them too much.

5) Not shown, but the top of the test section was covered. This is vital to keep laminar flow consistent throughout the test section.

6) Taped/glued the sections together

Had a 300-pack of straws. The nearest square less 300 was 17^2 = 289, so I decided to make a 17 by 17 grid of straws. I used books to keep straw layers consistent, and constructed them one at a time. Once all layers were made, I taped each layer together. I used their natural grooves to build them in a left-right-left-right pattern. This does result in the straightener being shorter than it is wide.

1) Flow straightener was raised

2) Measured cardboard, sketched cut lines, and made 2 symmetrical top/bottom pieces. If you have the cardboard, I recommend making four, as you can then skip the next step.

3) Made the other two sides with the little remaining cardboard I had along with some index cards.

4) Tape everything together. Make sure to avoid leaving gaps.

The contraction area was built directly onto the flow straightener.

First, the flow straightener was raised using a combination of books and a plastic bin. Then, I measured and cut cardboard to have a 2 symmetric sides for the top and bottom. Unfortunatelty, I did not have enough cardboard to make 4 sides, and the parts that could not be covered in cardboard were instead covered by index cards.

The purpose of the contraction area is to channel all the air pulled in by the fan into the wind tunnel. It must be noted, however, that contracting flow changed flow pressure and speed, as dictated by Bernoulli's equation.

1) Put the box fan into its place. Used string to keep the boxfan fully upright @ ~90 degrees, otherwise, it was tilted slightly up.

2) Further supports were added to keep the structure from sagging and being uneven.

3) Supports were modified with different books, magazine, etc. to have equal height.

This is a step that can be done alonside the previous few. In fact, it may be better structurally to do so.

1) Index cards were used to cover any gaps in the contraction area. For example, the areas next to the corners of the box fan were covered.

2) A small kitchen scale was placed inside the test section, with the information panel facing the back, as shown in the next step.

Before running any experiments or projects in the wind tunnel, I tested the fan in the tunnel. What I found was that a lot of air escaped through every single gap.

1) Make/bring something to test. I used a big ramp to generate downforce.

2) Place the test object on the scale, then tare the scale so that it reads 0.

3) Run the fan! At level 1, I got ~0.9 grams, at lvl 2, 1.9 grams, and at lvl 3, 3.3 grams.

If the scale says 0, consider increasing the area of your test objects lift/downforce surfaces, as they may not be generating enough force to "trip" the scale. That is why my lego object has a index card attached to its rear.

In the future, I hope to acquire lexan or use some other material to make my test section fully sealable. Then, I would 1) turn the fan & test section around to turn the contraction area into a diffuser, and 2) build a intake area.

In addition, I would add some visualisation fluid like dry ice vapor to complement the kitchen scale.

For now, that's all. Was a fun project, and very cheap too. The only thing I had to buy was 300 boba straws for ~ 9 dollars.

Thanks y'all!