Wind Tunnel for Small Models

This is a wind tunnel that is perfect for small, 3D printed scale models of airfoils and other things! Easy and affordable to assemble, and very easy to use, this wind tunnel is perfect for class projects and experiments involving fluid dynamics and lift/drag analysis. Do not let its wooden structure deceive you, its humble 50 cm by 8 cm size is enough for laminar flow and large enough for placing in and testing cheap and scalable models of anything, from a model turbine to an airfoil, and anything else you'd like!

Supplies

To the wind tunnel itself, there are only four main "materials," namely, balsa wood, straws, an acrylic sheet and a DC computer fan. The balsa wood and acrylic were purchased at Michaels, but can also be bought at Hobby Lobby or Amazon. The straws (about 150 in use) were purchased at Walmart. The fan was purchased on Amazon. Additionally, a hot glue gun, some thin coffee stir sticks, and black paper were used as well.

For the convencince of everyone, here are Amazon links for the materials used and their respective prices.

List:

Balsa wood (FOUR 4" x 12" sheets): $9.99

https://www.amazon.com/CRAFTIFF-Sheets-Unfinished-Pieces-Crafts/dp/B0893W2BXH/ref=sr_1_5?crid=EW70CZXC5BN4&keywords=balsa%2Bwood%2B6%2B12&qid=1699514601&sprefix=balsa%2Bwood%2B6%2B12%2Caps%2C113&sr=8-5&th=1

Stir Sticks: $7.99

https://www.amazon.com/Count-Inch-Wooden-Coffee-Stirrers/dp/B093298WC3/ref=sr_1_6?crid=V5FCIDXR2788&keywords=stir%2Bsticks&qid=1699514467&sprefix=stir%2Bsticks%2Caps%2C119&sr=8-6&th=1

acrylic ( any clear plastic sheet of at least 2mm thick should work): $6.99

https://www.amazon.com/Langaelex-Thickness-Extruded-Plexiglass-Replacement/dp/B09KXZCPWR/ref=sr_1_6?crid=2G2E2OJT6HR0O&keywords=5%2Bx%2B7%2Bacrylic%2Bsheet%2B2mm%2Bthick&qid=1699514700&sprefix=5%2Bx%2B7%2Bacrylic%2Bsheetv%2B2%2Bmm%2Bthick%2Caps%2C107&sr=8-6&th=1

Straws: $6.99

https://www.amazon.com/Plastic-Neon-Disposable-Drinking-Straws/dp/B07L8MK983/ref=sr_1_5?crid=9EG22J5B8TYN&keywords=150%2Bstraws&qid=1699514863&sprefix=150%2Bstraws%2Caps%2C108&sr=8-5&th=1

80mm x 80mm DC fan: $7.11

https://www.amazon.com/dp/B071WLX5JZ?psc=1&ref=ppx_yo2ov_dt_b_product_details

Also needed will be 1 rubber band and 1-2 pieces of paper, preferably black construction paper.

A strong glue gun is what I used for this project and what I recommend, although a typical glue gun should work well. I also recommend looking at local stores for better prices and quantity of goods.

I also use a 2 AAA battery holder, but a 9 volt battery can work as well. Voltage should be above 1.5 V, I am working with 3 V.

Step 1: Inlet and Laminar Flow Assembly

The first thing to make is the inlet, made up of the straws, which allow for laminar flow into the tunnel itself. If not present, the airflow in the tunnel is turbulent. The straws are necessary to straighten out the airflow from the fan before reaching the tunnel so that we can see changes in airflow over an object placed in the tunnel.

First, assemble the inlet out of the rubber bands and the coffee stir sticks. The fan I am using is 8cm by 8cm and first cut 4 sticks out of the stir sticks measuring about 8.2 cm (the additional 2 mm is for offsetting with the other sticks) hot glue the edges and let it dry. Repeat two more times, stacking frames on top of each other.

Then attach the fan by gently fitting it into the frame. DO NOT GLUE THE FAN TO THE FRAME. This is to make sure the size fits. Remove fan when satisfied with size and fit.

Then, using sharp scissors or a knife, cut the straws from the base to the bottom of the bendable section, or about 5.5 inches (14 cm). Take the rubber band and wrap it around the straws until the diameter is about 80 mm. Place the straw bundle in the center of the wooden frame, and glue a frame out of the stir sticks to hold the straws in place. Glue the gaps between the straws and the frame, and add more straws where needed. The corner gaps should be covered with paper to prevent back flow.

When glue between straws and frame has dried well enough, the fan can be placed back to test fit. Splice fan connection and attach to battery holders if available/desired.

Step 2: Tunnel

As in Step 1, a frame should be made, but this time it does not need stacking, nor should it be glued to the straws or the fan.

Next, take the balsa wood and cut out 4 pieces that are 8cm wide and at least 30 cm (12 in) long. Glue one wide edge (8cm) to the INSIDE of the frame. Let dry before gluing second piece. Let dry before gluing third piece.

The forth piece will contain the viewing port. If using a 5x7 acrylic sheet, cut out an area in the center of the last piece just slightly smaller than 6 in long and leave 0.25 in at the bottom. Reference clear acrylic sheet and make sure to leave overlap. Place the acrylic sheet over cut out area, and glue stir sticks around border of sheet. Do NOT glue sheet to sticks or balsa wood. Add framing with stir sticks on edges where necessary. Remove acrylic sheet, notice it should slide outward of the pocket you just made with the sticks and the balsa. Glue final wall to complete tunnel. Trim and paint as desired.

(Optional but recommended, cut out 2 strips of paper 8cm x 30 cm and place on inside of tunnel, opposite of the viewing port and one on the floor. This will allow our viewing of the flow to be seen more easily)

Step 3: Assembly and Test

Take the inlet and fit it into the tunnel, the distance of the inlet into the tunnel can be adjusted as necessary. The straws ended up near the edge of my viewport. Turn on fan with battery to see if it works, if the fan spins, congratulations! You have a wind tunnel! However, this can seem slightly dull if we have nothing to test, or if we cannot see the airflow. Print out or place any object that will fit into the wind tunnel, whether it be a airfoil, a mini airplane model, or a toy car. I used an airfoil, which I attached to a cut straw and placed on a rail I've used for other experiments (See attached if desired).

To see the airflow, two things are required, a good light source (I recommend a flashlight at the exit of the tunnel) and some dry ice, which can be bought at a convenience store. place a small amount of dry ice in a small cup or bowl, and then fill the bowl 75-80% with warm to hot water. The vapor produced by the dry ice should be dense and fast. Place this bowl in front of the running fan and you should be able to see the airflow into the wind tunnel and around your object.

Looking forward to see what others can do with this, Enjoy!