I've observed this effect using a "Zero Blaster" fog ring gun. The package indicated that "technique" was required for optimal performance, so I practiced and was eventually able to make super rings that were star-shaped and would travel faster, straighter (for a time), and further than an ordinary circular ring could. They also had other interesting properties...
I watched these super rings transition from their star-shape (usually 4 to 6 points) to an ordinary circular ring once enough energy had been lost to air friction. Upon "decaying" like this, the whole ring experiences severe turbulence - strong enough to eject parts of the ring from the body before it suddenly re-stabilizes as an ordinary circular smoke ring. It also abruptly changes direction (slightly) and continues to travel at a slightly reduced speed. The bucket experiment is quite different because it's externally powered and thus won't decay.
The ring decay phenomenon was very interesting to me and, combined with the star shapes, gave me the first clues about what's going on and I'm now sure of the solution and that it applies to the bucket experiment too. The theory I came up with was that two vortices are working together to create this effect. The primary vortex is, obviously, the toroidal flow of the smoke ring and the axial flow in the bucket. The secondary in both cases wraps around the primary like a candy cane and makes some number of complete turns around it so it meets-up with itself to form a stable closed-loop vortex.
The fact that regular geometry pops out of this should be no mystery then. Consider that the secondary vortex, however initiated, is likely powered & controlled by the primary and is thus bound to it. As it wraps around the primary, it must make a whole and complete number of turns around it or one of its up-flows will meet a down-flow and it negates its own energy, hence the turbulence and ejected fog during the decay process, which is simply when the secondary fails. Thus, you see what is stable and lasts and not those which don't - a conclusion of profound simplicity.
I noted other observational evidence supports the secondary vortex. In my experiments, this fog was heavier than air and because of that, ordinary circular rings begin to sag and eventually "drip" fog after a time. The fog contents of these star-shaped rings is clearly and visibly rotating axially (perpendicular to the primary) while traveling, however without rotating the ring itself (if you can imagine that - just the fog rotates within a non-rotating star-shaped ring) and keeps the ring from sagging - at least until the ring decays to an ordinary circle in the end anyway.
This theory could be perhaps be verified with a bucket experiment, which I will not attempt, by adding colored dye high-up or low-down and in a corner formed by the air gap opened up by the vortex. If there is a secondary vortex present, the dye should move from top to bottom and/or vice-versa quickly - before it reaches the next corner in fact, as each corner of the shape should represent a complete turn of the secondary vortex around the primary. These results would be interesting to know, but not so useful to me hehe.
Slashdot Mirror
I've observed this effect using a "Zero Blaster" fog ring gun. The package indicated that "technique" was required for optimal performance, so I practiced and was eventually able to make super rings that were star-shaped and would travel faster, straighter (for a time), and further than an ordinary circular ring could. They also had other interesting properties...
I watched these super rings transition from their star-shape (usually 4 to 6 points) to an ordinary circular ring once enough energy had been lost to air friction. Upon "decaying" like this, the whole ring experiences severe turbulence - strong enough to eject parts of the ring from the body before it suddenly re-stabilizes as an ordinary circular smoke ring. It also abruptly changes direction (slightly) and continues to travel at a slightly reduced speed. The bucket experiment is quite different because it's externally powered and thus won't decay.
The ring decay phenomenon was very interesting to me and, combined with the star shapes, gave me the first clues about what's going on and I'm now sure of the solution and that it applies to the bucket experiment too. The theory I came up with was that two vortices are working together to create this effect. The primary vortex is, obviously, the toroidal flow of the smoke ring and the axial flow in the bucket. The secondary in both cases wraps around the primary like a candy cane and makes some number of complete turns around it so it meets-up with itself to form a stable closed-loop vortex.
The fact that regular geometry pops out of this should be no mystery then. Consider that the secondary vortex, however initiated, is likely powered & controlled by the primary and is thus bound to it. As it wraps around the primary, it must make a whole and complete number of turns around it or one of its up-flows will meet a down-flow and it negates its own energy, hence the turbulence and ejected fog during the decay process, which is simply when the secondary fails. Thus, you see what is stable and lasts and not those which don't - a conclusion of profound simplicity.
I noted other observational evidence supports the secondary vortex. In my experiments, this fog was heavier than air and because of that, ordinary circular rings begin to sag and eventually "drip" fog after a time. The fog contents of these star-shaped rings is clearly and visibly rotating axially (perpendicular to the primary) while traveling, however without rotating the ring itself (if you can imagine that - just the fog rotates within a non-rotating star-shaped ring) and keeps the ring from sagging - at least until the ring decays to an ordinary circle in the end anyway.
This theory could be perhaps be verified with a bucket experiment, which I will not attempt, by adding colored dye high-up or low-down and in a corner formed by the air gap opened up by the vortex. If there is a secondary vortex present, the dye should move from top to bottom and/or vice-versa quickly - before it reaches the next corner in fact, as each corner of the shape should represent a complete turn of the secondary vortex around the primary. These results would be interesting to know, but not so useful to me hehe.