Wind Tunnel Testing Now Available To The Common Man

DIY Wind Tunnel

If you are in the market for a DIY wind tunnel the folks over at sciencebuddies.org have got you covered. They have done a great job documenting how they built their own wind tunnel. Most of the structure is made of plywood with the test chamber is made of plexi-glass so that the operator can visually observe what is happening during a test. A common gable-mount fan provides the air flow, you may have one installed in your attic to keep it cool. The only non-widely available components are the force sensors that feed data to a computer for logging.

airflow through a wind tunnel

This DIY wind tunnel works the same way as most open-circuit wind tunnels do. Air enters the Contraction Cone, where the inlet is larger than the outlet. This reduction in chamber size speeds up the air as it enters the tunnel. The air then passes through a Settling Chamber that straightens out any turbulent airflow by passing the air through a screen or mesh. Up next is the Test Section where the model is mounted on force sensors. The sensors in this particular wind tunnel are set up to measure the force resulting from the air pushing rearward on the model (think drag) and also how much lift is generated from the geometry of the model (in this case an airfoil). By the time the air reaches this point it is moving straight and parallel with the tunnel which avoids unwanted forces from turbulent air applied to the model. Ideally, all forces applied to the model will be a direct result of the aerodynamic properties of the model. Any wind speed sensors would also be placed in this section. Rearward of the Test Section is a Diffuser which is a chamber that slows down the air by gradually increasing in cross-sectional size. The final portion of the wind tunnel is the Drive Section that contains the fan. Having the fan at the end of the tunnel almost sounds counter-intuitive but doing so reduces turbulence of the incoming air.

Comments

  1. Biomed says:

    Pressure sensors are more important than wind speed, but still locked in their relationship. Some terms to know, are viscosity, laminar flow, and Reynold number is a huge item to understand, then terminal boundaries, boundary flow, boundary layer, boundary separation…. then NACA, stop here, heck with it… this is a whole ‘nother field just as complex and complete as electronics that allows calculation of wings thru propellers. It’s a whole second library of books too! Luckily the same books apply to gasses as well as liquids with just the viscosity changing (hence hydrofoils become easy as well.). Wright brothers built their own tunnel for testing… My friends, welcome to a whole new world to explore (if you’ve not already invaded it).

    Best thing is your electronics mind is totally suited to the work already!

    • scorinth says:

      My fluid mechanics class alone pushed me over from “probably going into industry with a bachelor’s” to “DEFINITELY applying for grad school.”

  2. Thinkerer says:

    For what it’s worth, the Wright Brothers did likewise. History seems to consider them to be some kind of yokel bike mechanics, though they were meticulous engineers – hackers of their day.

    http://www.grc.nasa.gov/WWW/Wright/airplane/tunnel.html

  3. JimBob says:

    I remember Estes Rockets published plans for a homemade wind tunnel. I seem to remember it was a squirrel cage fan powered with a bicycle drive.

    • David says:

      I made my own wind tunnel back in the 70’s. Did slow-mo 8mm of white smoke flowing over different wings. Best part was the science teacher taught me how to make great white smoke – equal parts salt peter and sugar….which lead to my exploration of making my own gun powder. Amazing what you can do in junior high!

  4. Nice plans in Scientific American Amateur Scientist section in about 1962. I dig the PowerMac. (Reynolds Number has an ‘s’.) I think the baffle should be stacked about 4 deep to work really well. Anyone know the proper length for eliminating turbulence of a certain size and fluid velocity? A big bundle of drinking straws works well for water. How long for air?

  5. Biomed says:

    Big bundle of drinking straws….. near the exact description of laminar flow transducers for precision measurement of gas/liquid flow rates. Quite precise and easily calibrated. .

  6. Galane says:

    What the Wright Brothers discovered was that small airfoils don’t scale up linearly to ones large enough for an aircraft to carry people. At a small scale, air functions as if it’s much thicker.

    Scale up something the size of insect wings to the size of a tennis racket, and slow the speed proportionately, to get the same forces the wings have to be moved in a light sugar syrup. There’s a guy doing exactly that because it’s far easier to observe the vortices that enable a bumblebee to fly when the wings are moving slow enough to see and don’t have to be viewed through a magnifier. ‘Course everything around his test rig is sticky from the sugary water splashing about. Sticky science…

    • lageos says:

      It scales with the Reynolds number, therfore it is possible. Problem is that if you want to explore something fast moving (i.e. airplane) a small model needs a high fluid velocity and that is a difficult task. Supersonic regime is another boundary (there aren’t many scientific supersonic wind tunnels at all).

      It would be possible to use for example water with a small model, or go to a large scale model with reduced fuid velocity.

  7. echodelta says:

    I have seen and touched their longer more curvy wooden tunnel in Dayton. The sharp angled intake is rough on flow, the light grid near useless.
    Up until the Wrights, sailing was the model for flight. It took bicyclists to realize it’s not just set for angle etc. It’s very unstable and needs lots of control. They had a plane that could fly straight and level in the 1870’s, but you could not control it.

  8. DougM says:

    Go down to the local furnace installer and ask for the squirrelcage blower off the dead furnaces they remove. They’ll give them to you for free and those things move a *lot* of air.

  9. Smorges Borges says:

    I remember the mechanical flight simulator wind tunnel in the Chicago Museum of Science.

    It was a long chamber with an air flow and a model plane with control surfaces you controlled. I thought it was really cool as a kid.

    Is it still there?

  10. Mental2k says:

    Seed the flow with some oil, laser and high speed ccd and you’ve got a piv setup. Probably doable for a reasonable price these days.

    As others have mentioned perhaps a better laminar section, but hey these things are modifiable.

    I remember seeing the tunnel at tu delft on a visit. Beast of a working section, I think they planned on using it for their formula student car.

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