Hackaday Prize Entry: Non-Computational Fluid Dynamics

Computational Fluid Dynamics, or CFD, and is applied to everything from aircraft design to how good of a wing a new skyscraper will be. Of course, the science of building airfoils is much older than CFD, leading to the question of how airfoil design was done before computers.

The answer, of course, is a wind tunnel. Walk around a few very good air museums, and you’ll find wind tunnels ranging from the long wooden boxes built by the Wright brothers to fantastic plywood contraptions that are exceptionally interesting to woodworkers.

[Joel] needed final project as an upcoming aeronautical engineer, but he wanted his project to be something physical, and a tool that could be used again. He decided to build a wind tunnel that’s also his entry for The Hackaday Prize.

This wind tunnel isn’t a gigantic device the size of a building. The very first wind tunnels were simple devices just a few meters long. With a fan at one end, a section to stabilize the wind, a chamber, and a place for the air to go, it’s also a very simple device. Just because something is simple doesn’t mean anyone has built one recently, though: [Joel] couldn’t find anyone who built a wind tunnel with step-by-step instructions. This project is just that – an Open Source wind tunnel.

The design of this wind tunnel is simple enough, built out of fiberglass with relatively simple molds. The design can be adapted to various electric fans, and the most fun part of the build – the smoke machine – is already complete.

21 thoughts on “Hackaday Prize Entry: Non-Computational Fluid Dynamics

  1. The trick is to get a laminar flow at your chosen airspeed so the smoke ribbons don’t break until they hit the airfoil.
    I did a science fair wind tunnel to show how a stall works by having a box fan, several small fans, several layers of screen, and then the best idea was several thousand bamboo skewers glued extending through the last three screen layers and into the airflow to break any spirals; so many nights of work while watching 321 contact and nova, my trs-80 got lonely. The whole thing in a 2.5m plexi and plywood tunnel for a model airplane with the engine removed(should have done just a section of airfoil). I used a smoke bomb and injected the smoke with copper pipe run through all layers of the screen. The trick was to make everything fight the spiralling of the fans and also break up the eddys from everything in the airflow, the skewers really helped. This setup was fragile and while it worked got a bit messed up schlepping it outside when they wouldn’t let me do smoke ribbons in the gym. Being America the 80s they at least didn’t arrest me for being a kid with a pyrotechnic device, though I can pass for white if I wear the right clothes.

          1. Those just have a bunch of soda straws in them which the water has to flow through. Essentially you’re forcing turbulent air or water through a lot of small passages to subdue the turbulence and make the fluid flow in a straight line.

    1. “..the best idea was several thousand bamboo skewers glued extending through the last three screen layers and into the airflow to break any spirals..”

      Do you have a picture/diagram/drawing of that somewhere please? Or a little more detailed explanation how the skewers sat in the flow and were mounted?
      Were the skewers perpendicular to the flow or in parallel to it?
      What size of tunnel did you have?
      How large were the skewers in comparison to that?
      The project this article is about doesn’t touch the stabilizer section at all.. I’ve collected a couple of articles from around the web and have some ideas how the big boys do it, but I’ve not seen someone mention skewers before :-)

      1. It looks like a good idea, but the length to cell size is too short. At least 5:1 is required to smooth out the imperfections. On top of that they create some turbulence with the flat faces down stream. Thin walled straws are really the best for straightening, though they can have high drag from the large surface which lets boundary layer develop. Still, it’s better to have low turbulence and pay for it with a higher electrical bill, particularly at the reynolds number of interest in tunnels this size.

    1. They use less power, and as mentioned can use different gasses or produce specific environmental conditions. Those criteria are typically far beyond what a user of a tunnel this size needs, and they can significantly increase the cost and complexity.

    2. You use closed loop tunnels to safe on energy costs for accelerating the air and conditioning it (dry/wet/hot/cold/etc..).
      For science projects or small tunnels one usually doesn’t need that, so the air is just recirculated within the room.

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