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Old Feb 07, 2002, 08:14 PM
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zagisrule!'s Avatar
Edgewood, NM
Joined Jan 2002
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Wind Tunnel Smoke

Hi!
I need to make smoke for my homemade wind tunnel for flow visualization.

Any ideas?
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Old Feb 07, 2002, 08:26 PM
high-speed freak
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San Jose, CA
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dry ice? don't want to light anything on fire...
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Old Feb 09, 2002, 04:08 AM
rebmeM roineS
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Incense sticks?
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Old Feb 09, 2002, 07:02 AM
jrb
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This is actually more of a challenge than you might think.

Asuume you are using a prop/fan to establish the airflow thru your tunnel?

How have you straightened (removed the swirl) the flow?

If the flow has much swirl to it, the smoke will defuse very quickly and you won't get a nice streamline effect.

If you can afforde the pressure drop a window screen works well, or use some sort of an egg crate/honeycomb.

Some folks have had success using smoke bombs in a coffee can with a tube for the smoke probe.

I used to use some chemical (its clear) that turns to a white smoke in the presense of air; don't remember what its called. I would stick a piece of balsl into the chemical and could get a point source of smoke or a "sheet" of smoke.

It worked well, though it couls stain plexiglass if not cleaned fairly quickly.
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Old Feb 09, 2002, 04:43 PM
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I am using a vacum cleaner for the air flow, and think dry-ice might be good.

Thanks!
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Old Feb 10, 2002, 04:01 AM
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Seattle
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Quote:
Originally posted by jrb
How have you straightened (removed the swirl) the flow? If the flow has much swirl to it, the smoke will defuse very quickly and you won't get a nice streamline effect.
The thing that came to mind was a stack of corrogated cardboard. Cutting a series of cardboard pieces about an inch wide and stacking them to fill the wind tunnel should align the flow.

Quote:
Originally posted by jrb
I used to use some chemical (its clear) that turns to a white smoke in the presense of air; don't remember what its called. I would stick a piece of balsa into the chemical and could get a point source of smoke or a "sheet" of smoke.
Heating and cooling shops use a smoke generator that consists of a small glass tube and a hand bulb. The ends of the tube snap off and the hand bulb pulls air through the chemicals inside. Each squeeze of the bulb produces a thin stream of white smoke. They use it to track airflow in forced air systems.

The cheapest way would be to buy a pack of Marlburos. Stick a cig in one end of rubber tubing and stick the bottom half of a bic click pen into the other. The vacuum in the wind tunnel should pull the smoke through the tube. Just inject it into the wind stream upwind of the smoothing vanes.


Silver
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Old Feb 10, 2002, 03:42 PM
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Gladstone, NJ. USA
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When I was in Junior High school...I fabricated a real working wind tunnel! It used a vaccum cleaner blower/sucker to generate the flow. through the approx 1.0" wide x 8" deep champber that was made of plexiglass on both sides. Light was generated by 4 50 watt light bulbs with black painted surface to show contast. The smoke generator consisted of a glass jar..Quart size Helmans mayonaise Jar! with metal cap. To this was soldered 2 tubes 1 for inlet (fresh air) the other connected via about 1 inch dia light rubber hose to the smoke distributor, which consisted of a streamlined balsa block with an adequate hole running down the center (span wise, if you will) to this was connected maybe 20 or 30 brass tubes that protruded from the trailing edge of the "block" by about an inch. getting back to the smoke generator...At first I used "Lionel" train smoke liquid! But then found that ordinary "Mineral Oil" worked just as good..and much much less expensive! If I remember correctly I had a wick...think it was some old dt fuse actually....and around that was wound a pc of Nichrome wire heated via a model train transformer. when the wick was soaked in Mineral oil and heated to the proper temp...Not too high..or it might eventually ignite! It produced great amounts of thick wihite smoke! (In the jar) which was then transported to the distributor and tubes via suction developed by the passing air over the tubes....It took a little sorting out to get the flows correct...but when adjusted the system would show very accurate lines of laminar flow over various shaped airfoils and shapes....It was quite an achievement for a 14 year old.! I won the Science fair! How ever I do remember that the "Fire department" was about to be called by the "Principle" until he noticed that my "Wind tunnel" was the source for all the smoke in the auditorium! Use some kind of ventilation sys and you'll be fine... By the way....Model Airplane News actually had a plan for this very wind tunnel...I guess you could call them to digh through their archives....from the late 1950's
Sincerely,
Jon B. Shereshaw
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Old Feb 10, 2002, 08:38 PM
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A real cheap laminiser can be made of a packet of drinking straws cut into 25-50 mm sections, then stacked up like firewood in the intake of the wind tunnel...
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Old Feb 10, 2002, 11:27 PM
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The drinking straws make a good air flow straightener. Fire works punk produces about 6" of decent smoke trail.
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Old Feb 12, 2002, 09:40 PM
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Thanks for the help!!!
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Old Feb 13, 2002, 05:30 AM
rebmeM roineS
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Rockingham, Perth - Western Australia
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Quote:
Originally posted by jrb
This is actually more of a challenge than you might think.

Asuume you are using a prop/fan to establish the airflow thru your tunnel?

How have you straightened (removed the swirl) the flow?

If the flow has much swirl to it, the smoke will defuse very quickly and you won't get a nice streamline effect.

I had imagined he would have sucked the air in, thats how I would do it.
That is, theres an open end to the tube, the opening is nicely rounded like a trumpet to allow smooth flow in, the model is positioned about mid way in the tube and the fan is at the other end, sucking the air through.
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Old Feb 13, 2002, 08:33 AM
jrb
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MrBungle, actually it doesn’t matter (in a subsonic tunnel, open or closed circuit) whether the fan is B4 or after the test section, swirl is still a problem. Though, the debris screen generally reduces this a bit.

Using a vacuum cleaner probably eliminates any swirl (fan induced) problems.

Will be in Perth (WA) in March, is there a lot of electric flight activity there?
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Old Feb 13, 2002, 01:27 PM
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Idaho
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This has got me somewhat interested. I am now wondering what size everyone uses for a wind tunnel? Is it pretty small and then you just reduce the size of the model you're producing or is it big enough to house a very large model? Also what is everyones tunnel made from.

Thanks for the help
Josh
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Old Feb 13, 2002, 01:35 PM
zen pilot
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milwaukee WI USA
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years ago i belonged to a rocket club that had a windtunnel. it used a blower froma furnce and paper towel cardboard tubes to straighten the flow. it worked very well but we didnt have smoke .the tunnel its self was made from plywood and was about two foot sqaure on the inside.good luck with your project.
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Old Feb 13, 2002, 03:08 PM
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San Jose, CA
Joined Sep 2001
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there is actually a guy on ebay selling wind tunnels every now and then, but they look like two fans with a pipe connecting them... doesn't sound nearly as good as the ones you guys have built! btw, what use is a wind tunnel without the smoke??

I am a bit curious what actual use a wind tunnel is for slow-flying models like ours... you can see the flow, I know but...
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