In high school, I struggled to find the tools necessary to test my aerodynamic prototypes. Testing a line of code, for example, is simple: you find the right development environment (IDE) and compiler, feed your code, look at what is wrong, and refactor your code prototype.
For aerodynamics, on the other hand, not very simple. Even if you are taking the computational/simulation approach, the least you have to do to make changes is redraw the CAD file for your prototype. For budding prototypers who don't have access to the computing power necessary, testing aerodynamic innovations is an impossibility. Unless, of course, you have access to a tiny windtunnel. I was in this precise state in my aerodynamics journey as a student in grade 12. "What if we made new holes in the wing?" I thought. What would it do for the lift of the aircraft. I wasn't able to understand how I could possibly test. I tried the simulation route, but having access to a computer system with enough RAM was tedious to work with. I knew one person with such a system - he was a professor at IISc. Using his system to test was tedious, nonetheless. What if I had to change something? What if he wanted to use it while my simulation ran? Many such variables makes this extremely impractical.
I had no choice but to build a windtunnel, and due to a lack of materials, a simple one out of scrap materials. I backed my design with research to produce the windtunnel project.
Full Tunnel Design
Biomimetics
Something important that isn't mentioned on the main website of this project is that the suction mechanism is inspired from nature. It is ridiculously hard to get clean flowing air on the corners of the rectangular cube.
The suction mechanism used by fish, specifically Micropterus salmoides in the study referenced [1], involves a combination of the mouth’s muscles and the ventral/dorsal ones that are primarily used to power their movements.
While attempting to find more power for the wind tunnel, the apparatus that directs air into its chamber to study aerodynamics, I mounted old PC fans to channel the air from the starting end.
This is inspired by the fish’s mouth movements that partially power their suction, leaving the heavy lifting to the rear muscles - similar to the main suction coming from the tunnel’s main power pod. The image shows the computer cooling fans mounted on the corners of the contraction section, replicating the mouth suction mechanism that initiates the flow but doesn’t fully power the suction.
Research Backed Design
To determine the correct length, angle, and dimensions of each of these components, I delved in the data provided by reviewing the literature of various researchers who studied the design of a windtunnel. It was at times difficult to determine the empirical benefits of a particular design; however, I completed this by running tests of my own. Below, I will provide an example of the design we developed of the flow straightener.
The flow stabiliser, as seen in the image adjacent, is the first component that the air entering encounters. After the air passes through a screen, it turns turbulent for a small length until it stabilises. The air must be allowed to pass untouched for a distance known as the settling distance before it enters the next component - the contraction section. This length is given by Bradshaw and Mehta's research who recommend a distance of 0.2 times the diameter of the opening.
The honeycomb is generally the first component that the flow encounters in an open circuit suck-through tunnel. Its purpose is to reduce large scale turbulence in the flow and remove twist from the incoming air.
A honeycomb is made up of several cells of a minute diameter. While a hexagonal shape is recommended, ours will be circular since we’re using straws to pan out the availability of the project.
Printable Plans
Since I knew the trouble of developing this apparatus, I found a way to provide a method to reproduce these. Anyone who whished to build a windtunnel now had access to this research backed design. Just like you can cut up six squares and glue them together to make a closed cube, you could download the design as a pdf and trace it over your material of choice to erect the windtunneld.
An example of such a pdf is here.
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