Visualizing the changes in air density with the Schlieren effect

By Shawn Knight · 8 replies
Aug 30, 2016
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  1. Odds are, you’ve probably never heard of the Schlieren effect (I hadn’t until today). In layman’s terms, it’s simply the ability to see changes in air density, like when you turn on a hair dryer or open a can of soda (we know air is rapidly moving, we just can't see it). That’s probably not a very helpful description but you’ll see what I mean in the clip above from YouTube user brusspup.

    Using a concave mirror, a light source, a razor blade and a camera, brusspup was able to visualize these invisible changes in air density. It almost looks like special effects or camera tricks but the user claims it is 100 percent science so I’ll take their word for it. All I know is that it’s incredibly impressive and I want to try it for myself.

    Found is a TechSpot feature where we share clever, funny or otherwise interesting stuff from around the web.

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  2. mbrowne5061

    mbrowne5061 TS Evangelist Posts: 747   +357

    I used to work in my Uni's supersonic wind tunnel. Schlieren lighting was how you capture the super-sonic air flow in its various stages. By focusing the light into the point, and then placing the razor blade right at that focused point, you can 'split' the entire image, allowing only one half to continue on into the camera lens. The result is that all the light distortions are visible.
  3. Adhmuz

    Adhmuz TechSpot Paladin Posts: 1,828   +633

    It's been features on several episodes of Mythbusters over the years, 100% a real thing and not simply camera trickery.
  4. stewi0001

    stewi0001 TS Evangelist Posts: 1,681   +1,080

    I'm still trying to figure out the purpose of the razor blade. All I can figure is that it is cutting down the amount of light coming to the lens.
  5. davislane1

    davislane1 TS Grand Inquisitor Posts: 4,736   +3,757

    It shaves down unwanted light to produce a silky smooth stream of visual distortions.
    stewi0001 likes this.
  6. Uncle Al

    Uncle Al TS Evangelist Posts: 3,321   +1,970

    LOL ..... we were capturing it on still camera's back in the mid-70's and it was nearly as incredible as trying to pump our high speed photographs up with some of the first electronic flashes .....
  7. So...why don't we just get a picture with a razor blade in the middle?
  8. mbrowne5061

    mbrowne5061 TS Evangelist Posts: 747   +357

    By placing the razor blade right at the narrowest point of the beam, you 'block' half of the information contained in the shadows. This leaves the light distortions 'unbalanced'. Think of the razor blade here like a diode in an AC-DC transformer. Looking at a normal AC wave, with an AC meter, and you will see a steady voltage. Place a diode in the circuit, and look at it with an AC meter, and you'll see just half of the Vpp - giving you an idea about the waveform itself.
    stewi0001 likes this.
  9. Uncle Al

    Uncle Al TS Evangelist Posts: 3,321   +1,970

    Exactly right, good answer .... glad you got to him before me, your answer was much more clear and avoided a 60 minute physics lecture! ROFL

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