Open Return Wind Tunnel With CNC Cutting

A student from Saint James High school in Hagerstown Maryland. Utilize CNC cutting, 3Dmodeling with Fusion 360, 3D printing, and other tools.

1. 2 pieces quater-inch thick wood cut board(24 inches*48 inches)
2. 4 pieces half-inch thick wood cut board(48 inches*96 inches)
3. 4 peices acrylic boards(36 inches*10 inches)
4. 4 pieces acrylic board(29 inches*30.5 inches)
5. screw and bolts(48 pairs)
6. Fan(19inches*19inches*7 inches)
7. fan information and source: https://www.lowes.com/pd/iLIVING-iLIVING-Automatic-Gable-Mount-Attic-Ventilator-Fan-with-Adjustable-Thermostat-3-10-Amp/1002542142
8. A metal mesh (19inches*19inches)
9. 10 piece cardstock(28inches*22 inches )

The contraction section is where the core of the whole wind tunnel. This section, with the bend of the acrylic board, creates an efficient proportion for air compression intake and maximizes the air speed passing through the test section. To create this contraction, we used a keel-shape board with the slope of the bend. It serves as the backbone of the acrylic board and reinforces the structure of the contraction from deforming. To ensure the structure is durable, we use the idea of mortises and tenons to stick each component together, with wood glue filling up the gapsChallenges:

Our first design was flawed in terms of conflict structure. Thanks to the modeling we did on fusion, we were able to figure out this issue before cutting the pieces out. By resolving this issue, we truncate the corner pieces into smaller pieces that fit in.

Mesurement of the Section:

outer box structure 30 inches*30 inches*30 inches

Cavity on the back(connection with test section) 10inches*10inches

This section consists of 4 pieces of acrylic board(36 inches *10 inches), 48 pairs of flat screws and bolts. Hold these four acrylic boards together in a tunnel shape. We used a 3D-designed locker to ensure that the four pieces of acrylic were in place. With 12 of these lockers and 4 pairs of flat screws and bolts on each locker. To further enhance the structure, we used silicon glue for the extra gaps.

Different from the contraction section, the test section should placed above the ground. For supporting and aesthetic purposes, we design a supporting portion of the test section. Analysis equipment should be placed beneath the test section.

This section is for the pulling of air into the system. The fan at the end tip provides a difference in air pressure within and outside the tube that pulls air from the intake section and forms a cycle of airflow.

The diffuser section consists of two parts. The main structure and the fan holder(with protection)

By using a similar method for the intake box. We utilize the idea of mortises and tenons to connect the four pieces of the main structure(with 5 degrees of tilting )and the fan box. 

When finished cutting, place the fan on the top and cover the fan with a fan box and a piece of mesh on the inside of the end hole.

Cutting Phase:

Application of Vcarve and Shopbot3

Contraction Section:

By using the tools in Vcarve, We have created the floor plan for the intake box. By adding the eight concavity for the convex part of the wave structure on each of the pieces. While doing so please remember to consider the thickness of the board used, to ensure that the inner measurements of the section are 30*30*30inches. Due to the shape of the drill being round, It can not cut out a square-shaped hole. Hence, the use of a dog bone structure allows the shopbot to cut the concave part.

Test section:

Use the cut tables to cut out crelic boards with measurement(36 inches*10 inches)

Using Fusion360 to create the model and print out using Ultimaker Cura

measure and then drill the hols on the acylic board to place the falt screws and the lockers.

Fill up the gaps by applying silicon glue.

Diffuser section:

finish cutting in addtion of applying the caulk in between the gaps to seel them.

The test section needed to be attached with the intake section. Hence, both test section and the diffuser section requires a levitation of 4.5 inches. 

Different from the previous cutting with vacarve. We utilize the Manufacture function of Fusion 360. This section allows cutting path based off the design model on Fusion and created a gcode that can be used for CNC cutting. 

We have decided to have all the sensors stored beneath the test section support, one piece of meter pointing in the horizontal direction, and one pointing up in the vertical direction. With these sticks and force meters, we are able to get the vertical (lift) and horizontal (drag) force of the test object. 

One of the design defects is that the rod going through a hole into the test section can not move on the horizontal piece. Furthermore, the midpoint is not locked with the test section. This means that the rod is not a lever system. In other words, the data from the force meter do not represent its exact lift and drag.

However, later through trials, we can figure out a variable constant based on this design.

The start of the intake section has an average wind speed of 1.6 m/s. Through the compression of the contraction section, the wind speed at the start of the intake section was 6.3m/s

We tested the wind tunnel with a wing prototype as the figure on the side shown. 

To lock the wings on the stick, we decided to temporarily use plasticine. The result wasn't promising. According to the reading from the force meter and the record on the logger pro, the wing is encountering  an average of 0.48 newtons of lift and 0.05 newtons of drag force

Force 1 verticle(lift)

Force 2 horizontal(drag)

The result indicates that the force meter barely read anything. 

Through observation, we think the problem of the test section is that how the wing is attached was somewhat inappropriate. The wing often turned to one side and as it did that, the lift drastically decreased.

Something taht is needed to be fixed;

1. Due to lack of material, we have portion of the curve in the intake section missing and some parts of the connection have minor gaps that can impact the air compression

Solution:

We decide to use poster paper and vinyl cover(stick them on paper to increase rigidity) to cover the acrylic.we add a combination of vinyl covers and poster paper to fill in the minor gaps(shown on the left)

Furthermore, we add extra foam in between the connection of the three sections to seal the gaps and increase the overall airflow performance.

The best representation of the lift and drag once turned on the fans is shown above.

Some of the experiments started when the fans started to run, hence taking the average value of the later parts of recorded data.

Furthermore, all data recorded should be the absolute value of the shown data.

As shown in the box on the left, the Delta Y is the max and mins of the noise.

The experiment data reflected the average lift and drag and all the data's R^2 values.Average Lift: 0.09437N

Average Drag: 0.1414N

Analysis:

Each force(horizontal and verticle components) has a outlier causing the R^2 value to be very low. Despite that, other datas are relatively consistant.

Contraction section fins angle source https://www.grc.nasa.gov/www/k-12/WindTunnel/windtunnel_report.html

Project foundation source https://www.sciencebuddies.org/science-fair-projects/references/how-to-build-a-wind-tunnel