Low speed wind tunnel - design and fabrication

In summary, the conversation discusses the building of a low-speed wind tunnel for a final year project. The size and configuration of the tunnel are mentioned, as well as the reading of papers on wind tunnel design. The conversation also includes questions about the differences between 2D and 3D tunnels, the necessary conditions for the wall profile of the contraction, and the fabrication of the contraction out of sheet metal. Additionally, the conversation touches on resources for obtaining information on wind tunnel performance and design. Lastly, advice is given to not build a wind tunnel for a project and a book recommendation is made.
  • #1
josh.k
1
0
Hello,

I'm a senior year ME undergraduate and I'm building a low speed (velocity=30-45 m/s) wind tunnel for my college as a final year project.

The initial size for the tunnel was 300mm x 300mm in the test section with an open circuit configuration.

I've read some papers on the design of a wind tunnel's components such as Design Rules for Small Low Speed Wind Tunnels - Bradshaw and Mehta, among others and I have some questions:

1. What is the difference, besides the obvious, between a 2D and a 3D tunnel? If size is a factor, what is the minimum test section size for a 3D tunnel?


2. For the wall profile of the contraction, if a defining equation is used, why is it necessary to have its second derivative zero at the two ends?


3. For the square contraction (area ratio 8 -12), if the equation for the wall profile is known, what method could be used to fabricate it out of sheet metal?

(I used NX sheet metal to develop one of the walls after i modeled it with a transformation of Bell and Mehta's curve, so that I could see its shape when unformed, if that could help, but I don't know what needs to be done after that)


Also, papers that have a lot of information about the performance and design wind tunnel components mostly have to purchased from their publications. Is there a source where these materials can be obtained freely?

If I have left out any relevant information, please let me know.

Thank you.
 
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  • #2
This advice may be a little late, but I suggest you do not build a wind tunnel for a project. I did something similar and it is too sensitive and there are too many parameters to consider.

A lot of the time, it is good to normalize or scale down ur wind tunnel for calculations. Were you looking for laminar or turbulent flow? The longer your wind tunnel is, the more developed your flow will become.

You could use straws or flow straighteners... but since you are using sheet metal, i assume you are riveting it together. These rivets will effect your flow near the walls.

You would need a real long wind tunnel also if ur inlet is 30 cm to get a fully developed flow. Check it w/ a pitot tube.
 
  • #3
You should get a copy of low speed wind tunnel testing by Pope & Barlow.

Barlow is a good guy, and his book is well written.
 

1. What is a low-speed wind tunnel?

A low-speed wind tunnel is a facility used for testing the aerodynamic properties of objects at low speeds, typically between 5-100 meters per second. It is designed to simulate the flow of air around an object in a controlled environment, allowing for accurate measurements and analysis.

2. How is a low-speed wind tunnel designed?

Designing a low-speed wind tunnel involves considering factors such as the required test section size, air flow velocity, and control systems. The overall design also includes components such as a fan, nozzle, contraction, and diffuser to create a uniform and stable air flow. Advanced design techniques, such as computational fluid dynamics, are often used to optimize the design for specific testing requirements.

3. What materials are used in the fabrication of a low-speed wind tunnel?

The materials used in the fabrication of a low-speed wind tunnel vary depending on the specific design and testing requirements. However, common materials include steel, aluminum, and composite materials. The test section, where the object being tested is located, is typically made of transparent materials such as acrylic or polycarbonate to allow for visualization of the flow around the object.

4. What are the benefits of using a low-speed wind tunnel?

The use of a low-speed wind tunnel allows for accurate and repeatable testing of objects in a controlled environment. This enables scientists and engineers to study the aerodynamic properties of objects, such as airplanes, cars, and buildings, and make design improvements to increase performance and efficiency. Low-speed wind tunnels are also more cost-effective than high-speed wind tunnels, making them accessible for a wider range of research projects.

5. How is data collected and analyzed in a low-speed wind tunnel?

Data collection in a low-speed wind tunnel involves using various instruments, such as pressure sensors, strain gauges, and flow visualization techniques, to measure and record the aerodynamic forces and flow patterns around the test object. This data is then analyzed using mathematical models and statistical methods to understand the behavior of the object and make design improvements. Computer software is often used to process and visualize the data, allowing for more detailed analysis and accurate predictions.

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