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I have to visualize flow over some designs in my wind tunnel. However, my advisor has stated that previous students have wrecked the machine when they have used oils and I think Dry Ice might interfere with the results owing to its different density and the fact that it will probably sink to the bottom of the tunnel (it is the horizontal kind).

Saif Ul Malook
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  • Do some baseline tests with object with known aerodynamic properties. – ratchet freak Jun 30 '17 at 11:23
  • Have you looked to see what, say, NASA uses, or what is recommended by any manufacturer of wind tunnels? – Carl Witthoft Jun 30 '17 at 14:29
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    Duplicate of How to make smoke for a small wind tunnel? – 410 gone Jun 30 '17 at 21:16
  • This question asks about a "smoke" like substance that leaves no residue. The apparent duplicate question & its answers do not address the issue of no residue remaining. This question is thus, not a duplicate. – Fred Jul 01 '17 at 11:59
  • @Fred that was precisely my issue with that thread. – Saif Ul Malook Jul 01 '17 at 14:46
  • And I have checked with the manufacturer (ELD). They dont have anything on their webpage and I believe NASA has huge wind tunnels that you can enter and clean up anyways. I havent found anything yet on these smaller ones. I will keep digging – Saif Ul Malook Jul 01 '17 at 14:48
  • I spent some time several years ago looking for something similar to inject into industrial compressed air lines feeding manufacturing machines. I wanted to demonstrate the appalling air leaks we had and locate them. I learned a few things: (1) Most (all?) gases are colourless. (2) Any kind of smoke is particulate. (3) DuPont apparently at one time made a red dye which might have worked for me. They discontinued it, as far as I know, because it gummed up the pneumatic valves. – Transistor Aug 29 '17 at 17:29

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In any normal wind tunnel, the wind speed will completely nullify the effects of thermal/density convection - unless you're testing some ultra-light apparatus that would work with airspeeds of order of 1m/s, just use dry ice - at ~5m/s airspeed the effects of density change and sinking rate will already be below threshold of other errors, and normally wind tunnel tests should involve airspeeds much higher.

SF.
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I would recommend using an ultrasonic fogger/mister in a containor with distilled water. You would have to pump some air into the sealed containor with a diaphragm pump and then have a line running from the other side of that containor to the location in the wind tunnel where you need it. The shorter the distance the better, but the ultrasonic mister should sufficiently atomize it to travel without much loss. Once in the wind tunnel it will disappear quickly as the mist evaporates. I would recommend just increasing the quantity of mist to go a further distance. It wont create a mess, since you can control how far it travels before the mist evaporates.

Here is a small unit Here is a larger unit

If you want to go the dry ice route you could do it the same way, as the "smoke" you see is just condensed water vapor from the dry ice temperature. The CO2 will proprell the mist so you won't need the diaphragm pump. It will just cost more labor/money if your test is very long or frequent. It will also be much more difficult to regulate.

Also, I agree with SF. that the density difference will not likely affect your results. The amount of visualizing mist is very small compaired to the primary wind tunnel stream.

ericnutsch
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