I used to notice something similar in college.<p><i>cough</i> 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.<p>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.<p>I don't know if this is related to the Two Vortex Ring Collision experiment, but it was definitely fun to watch!
There's also 12 hours of footage of all of the stages of the experiment on his second channel: <a href="https://www.youtube.com/watch?v=Cm9l8-qngjM" rel="nofollow">https://www.youtube.com/watch?v=Cm9l8-qngjM</a>
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.<p>This comment would have been better with a whiteboard.
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.<p>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.
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.<p>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.
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.