
Two Vortex Rings Colliding in Slow Motion [video] - cptroot
https://www.youtube.com/watch?v=EVbdbVhzcM4
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JohnDotAwesome
I used to notice something similar in college.

 _cough_ We were smoking a lot of... various things. I had setup a chill room
that didn't have any air conditioning (so it was actually very hot; a hot box
if you will). Just a small room where smoke would accumulate.

At any rate, I got very good at blowing smoke rings. In the still room, you
could blow a smoke ring and it would expand for about a minute before
dissipating. The more substantial rings would do something really crazy.
They'd spawn a new, smaller ring, but going the opposite direction. I believe
this was only the case if the ring was blown upward.

I don't know if this is related to the Two Vortex Ring Collision experiment,
but it was definitely fun to watch!

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tlarkworthy
Vaping and youtube has taken smoke ring blowing to new level
[https://youtu.be/zVXR7xttUeo](https://youtu.be/zVXR7xttUeo)

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TheSpiceIsLife
I don't see any reason why this shouldn't be an Olympic sport.

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cptroot
There's also 12 hours of footage of all of the stages of the experiment on his
second channel:
[https://www.youtube.com/watch?v=Cm9l8-qngjM](https://www.youtube.com/watch?v=Cm9l8-qngjM)

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theothermkn
The reason for the secondary rings, and the explanation for their outward
travel, is a straightforward application of potential flow, namely that lines
of vorticity induce rotational motion that falls off at 1/r. As the rings
approach each other, they induce outward motion, and any instability or
imperfections in the rings cause closer points between the two rings to induce
more motion. With a bit of mental squinting, you can see how the primary rings
would pinch off to form the secondaries. A similar thing can happen to
passenger jet contrails, causing paired contrails to form a string of rings.
Conspiracy enthusiasts point to these as evidence for “Aurora” or other exotic
propulsion schemes, but they’re really just a rolled out version of the
phenomenon in Dustin’s tank.

This comment would have been better with a whiteboard.

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eponeponepon
> This comment would have been better with a whiteboard.

Actually, I think you nailed it. I'm no physicist, but you made the mechanism
behind it very clear and intuitive :)

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knolan
Herein lies a lot of the difficulty in doing experimental fluid mechanics. My
own PhD ended up conprising a few minutes worth of data after years testing
and retesting.

That said, I wonder if such an experiment would be better with PIV or even
Schlieren as there would be no need to refill the tank each time.

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Firerouge
The uncut video made it sound like a motivation for replicating the research
was to see if the number of secondary vortices were a function of the
velocity; however, it's not clear if that was ever determined.

Hopefully these videos and the specially built machine helps additional
scientists to study this effect and come up with more answers and conclusions
about what's going on here, as it still seems largely shrouded in mystery.

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exabrial
Destin is an incredible dude! Humble, kind, and really smart

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ehsankia
Him and his family are truly role models for how I want to be when I grow up.
Easily one of my favorite creators.

I mean, look at this!
[https://twitter.com/smartereveryday/status/10084779939482828...](https://twitter.com/smartereveryday/status/1008477993948282880)

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akeck
Congratulations, Destin! Amazing story, amazing result, amazing video. Three
years is a long time. Thanks for sticking with it.

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_audakel
wow there was a beautiful video. I like at the beginning how he explains how
difficult it was to actually create this experiment, so I could understand how
important this actually was. Also that it hasn't been done in like 40 years or
whatever.

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ztratar
3 years is a long time. I appreciate that people like this exist.

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ojuara
I second this. Really great!

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pvsukale3
Can this be recreated accurately using something like blender?

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ta848347
I think something like Ansys would be more suitable.

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rambossa
Implications of this?

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ISL
Thanks for the reminder that the internet is good.

