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"Hand Held" Supersonic Wind Tunnel, and you probably already own one.

AaronT

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This is pretty simple guys.

If you have ever removed the optics from a laser then shined the "flashlight beam" around you are 99% of the way there.

If you have notice the sharp shadows it cast and made some shadows you are 99.99% of the way there.

Do you have a can of "air duster"?

Possibly a new picture fad in the forum...

Using your laser project to show off color and supersonic "shock cones"

Setup


Results










Crummy pictures from an Iphone 4 on max diigital zoom. I think with a bit of an extended trigger for the can and my Iphone set to 1-1 zoom I can do better.

Some of you guys should be able to stun us with absolutely amazing photos.
 

Benm

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That would involve using a mirror though?

I think what we're seeing here is just changes in speckle, and i'm pretty sure that gas doesn't exit a spraycan like that at supersonic speeds.

I must admit they look a bit like mach/shock diamonds, but their cause is completely different.
 

AaronT

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That would involve using a mirror though?

I think what we're seeing here is just changes in speckle, and i'm pretty sure that gas doesn't exit a spraycan like that at supersonic speeds.

I must admit they look a bit like mach/shock diamonds, but their cause is completely different.
It only takes about 60psi to push air to mach in the right conditions.

Those conditions include air compressors and most aerosol propellant cans.

The air duster can cools and the pressure drops, the can has to be room temp for this to work. It works better the warmer you get it.
 

AaronT

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Resembles Schlieren photography.
Video. Take a look. https://youtu.be/UqyBK61favs
Spot on, the method I'm using simply forgoes the mirror. I may dig out some candles or light some matches to demo using this setup.

I'm using source that is more than 2 watts. I don't need the mirror to boost the light source. I can simplify the design.

I would call this a Schlieren Projector, and I am attempting (lamely) to photograph the projection.



I am never too eager to hook things to computers. If I had a good "HD" cam, I have a 10 foot chunk of aluminum I-beam I could build into a dedicated Schlieren device, at that point, I might want to consider a large volume air compressor and a loop of 1 foot pipe that narrows to some 6 inch clear tube for a larger scale supersonic air tunnel. It would also double as a subsonic air flow tunnel by swapping in a 1 foot size chuck of clear.



I think this month I will play with what I have, add a dry erase board as the projection surface. Then see if I can work out the math for the shock angles, calculate speeds etc. I may pick up a cheep air compressor from the pawn shop.
 
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paul1598419

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I seriously doubt the gas escaping the can is traveling at at least 1116.5 feet/second. That is the lowest mach speed there is. It is likely caused by the difference in temperatures between the air and the escaping gas.
 

AaronT

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I seriously doubt the gas escaping the can is traveling at at least 1116.5 feet/second. That is the lowest mach speed there is. It is likely caused by the difference in temperatures between the air and the escaping gas.
A tank pressurized to 35psi (air duster is between 75 - 100 psi) has a 3 micron hole, air escapes at a rate of at least 100 cc/m (dunk and bubbles captured) indicating a gas velocity of .82 or so (with the resistance and pressure of being submerged).

When you double velocity energy x4s.

A gas pressure of anything over 75 psi is plenty to push an air stream super sonic.

The shape of the hole in the tank matters quite a bit. The Straw in the air duster is pretty ideal. No straw at all is dramatic but sucks up liquid spoiling the shots.

It is not likely the hole in the tank observed was ideal, it was a rupture from an external impact.

 
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paul1598419

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While in fluid dynamics fluids can be made supersonic, what you are filming is likely not. If you are using a tube at the end of the can, the gases escaping the tube is not supersonic. If you have a link to a formula that proves your point, provide it. What you have here proves nothing and I'm too lazy to go looking for one.
 
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AaronT

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Q = V*A*K Flow Rate Calc

Yet once again, I will state simply, getting supersonic flow from just 60psi is reasonable...

"air duster" is 75 - 100 psi...

Go, test, verify, don't be lazy when you have the answer a few keystrokes away, just because you already know the answer will prove your knee jerk assumptions wrong.
 




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