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Budget ~$5k

Current setup: 2x 20k cfm water-based smoke machines facing each other 6' apart blowing across the top or bottom of a fan or set of fans. I was hoping there could be a way to get a vortex that rose in the sky using a series of fans. I've searched youtube and google to find someone who has done this because I feel like I've seen it before, but they've been no help. This is for a work project in defense.

Limitations: I can't use heat to get the smoke to rise higher due to fire risk.

Specific recommendations on: types of industrial fans to use, many small fans vs a few big fans, configuration/setup, all given the budget above would be very helpful. While googling, I found industrial high-velocity fans like this, but they claim to only project <=100' each, which would be underwhelming for me. I know this a fluid dynamics problem, so even recommendations on a setup that would expedite testing for height would be much appreciated.

Thank you!

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  • $\begingroup$ Even the output from big chimneys gets dissipated by the wind aka atmospheric movement so what do you expect? $\endgroup$
    – Solar Mike
    Sep 7, 2023 at 6:43
  • $\begingroup$ That's a feature for me, not a bug. However, I would like to preserve vertical velocity as much as possible, so as still "chimney" in high-ish winds (~15kts sustained). $\endgroup$ Sep 7, 2023 at 6:49
  • $\begingroup$ maybe a starting point ... science.org/content/article/surprise-tornadoes-form-ground $\endgroup$
    – jsotola
    Sep 7, 2023 at 16:36
  • $\begingroup$ Won't work. If it rises, then it is less dense. If it is less dense, then it will initiate the Rayleigh-Taylor instability. en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instability. Vortex structures can be long-lived, but may or may not have captured the material in the core. But it doesn't matter - you can't generate the sort of vortex that is stabile over time and space using a relatively small device. The machine has to be bigger than the effect. (think big jet engine creating a little vortex at the intake.) $\endgroup$
    – Phil Sweet
    Sep 8, 2023 at 17:43
  • $\begingroup$ Thanks for the feedback. I think there's a misperception about this. I'm not looking to create a tornado/vortex. I'm merely looking to extend the "throw range" of these fans with water/glycol particulate in them. I'm hoping that by arranging my fans, I can extend that range. Any extension would be a win. Thanks! $\endgroup$ Sep 8, 2023 at 22:38

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Your objectives and constraints are not clear, but based on your comment that you "merely looking to extend the 'throw range' of these fans", you may want to consider using an air vortex cannon. The best engineering solution, however, might be to see if you can mitigate the fire risk so you can use real smoke.

Air-Vortex Cannon

As @Phil-Sweet notes in their comment, simply trying harder to force a fluid through a fluid doesn't usually extend the range much because the fluid jet disintegrates because of instabilities. Suitably generated toroidal rings, however, can propagate stably for considerable distances. Check out:

There are at least a couple of potential issues. First, such a cannon is pulsed not continuous. Second, the air vortex can propagate long distances, but the water/glycol "smoke" may become invisible long before the toroid reaches its maximum range.

Buoyant Gases

You could entrain your water/glygol smoke in a buoyant gas, but I think they are all either dangerous/flammable/explosive (e.g. hydrogen and methane), or too valuable and expensive (e.g. helium and neon).

Mitigate the Fire Risk

Since we know that actual smoke from a fire can rise extremely high in the atmosphere, your best approach might be to try to figure out how the fire risk can be mitigated sufficiently to allow using actual smoke or hot-air driven particulates, e.g. rent a barge and do your experiment in the middle of a large lake.

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  • $\begingroup$ And will you get permission to build a large bonfire in the middle of a lake? pollution? removing the remains? $\endgroup$
    – Solar Mike
    Sep 13, 2023 at 7:00
  • $\begingroup$ @Solar-Mike A fire on a barge was just a possibility. It is not clear how "huge" the fire needs to be. People get permission to fire off spectacular amounts of polluting fireworks from barges . Fire researchers burn large structures on land, e.g. this or this. Very large public bonfires are not rare, e.g. Burning Man, summer solstice, Guy Fawkes night, 11th night, … $\endgroup$ Sep 13, 2023 at 15:43
  • $\begingroup$ Bet they guarantee the clean up afte the public bonfires... $\endgroup$
    – Solar Mike
    Sep 13, 2023 at 16:23
  • $\begingroup$ Unfortunately, this isn't a one-off test and any kind of fire is un-possible due to how these will be employed. I appreciate the thorough response! $\endgroup$ Sep 17, 2023 at 18:36

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