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Author Topic: Sound barrier - pictures?!?  (Read 14366 times)

Offline Alandriel

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Sound barrier - pictures?!?
« on: 05/10/2007 20:48:28 »
A friend of mine sent me an email containing images similar to the ones below.

Is this for real or is someone having a really good time with photoshop?











 

another_someone

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Sound barrier - pictures?!?
« Reply #1 on: 05/10/2007 21:19:34 »
I suspect they are real, but in particular atmospheric conditions (at least plenty of moisture, since it looks like condensation or ice being created behind the shock waves).
 

paul.fr

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Sound barrier - pictures?!?
« Reply #2 on: 06/10/2007 16:46:55 »
I think it is more to do with air molecules under a large force, the force of the air being moved at great speed as the plane moves them whilst going supersonic.
 

Offline DoctorBeaver

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« Reply #3 on: 06/10/2007 17:54:07 »
What would that look like to a ground-based observer? Or on a radar screen?
 

another_someone

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« Reply #4 on: 06/10/2007 18:37:52 »
I think it is more to do with air molecules under a large force, the force of the air being moved at great speed as the plane moves them whilst going supersonic.

Air, even under pressure, is transparent - to see something, you need impurities in the air.
 

paul.fr

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« Reply #5 on: 07/10/2007 10:33:04 »
Quote

A sonic boom is the thunder-like noise a person on the ground hears when an aircraft flies overhead faster than the speed of sound—supersonic.

Air reacts like a fluid to supersonic objects. As the aircraft travels through the air, the air molecules are pushed aside with great force and this forms a shock wave much like a boat creates a bow wave. The bigger and heavier the aircraft, the more air it displaces.

On the sea, there are small ripples in the water. As a boat slowly passes through the ripples, they spread out ahead of the boat. As the boat moves faster, it breaks through the ripples more quickly, forming waves. If it goes fast enough, the waves can't spread out fast enough, and they form a wake. It is formed out of all the little waves that would have spread out ahead of the boat, but couldn't, because of the boat's speed.

When a plane travels through the air, it produces sound waves. Sound waves are not visible. If the plane is traveling slower then the speed of sound, then sound waves can spread out ahead of the plane. If it breaks the sound barrier and flies faster than the speed of sound, it produces a sonic boom when it flies past. All the sound waves that would have normally spread out ahead of the plane are combined together, and boom sound is produced.

Boats moving rapidly through water create bow waves.When you're on the shore of the ocean and a boat zooms past, at first there is no disturbance in the water, but shortly after, a large wave from the wake crashes up to the shore. When a plane flies past at supersonic speeds, the same thing happens. Instead of the large wake wave, you'll hear a sonic boom.

When planes fly through the air at moderate speeds, the air molecules have time to move aside to let the plane through. If the aircraft goes too fast, though, the molecules can't move aside, and the plane slams into them-boom!


http://www.nasaexplore.com/show2_912a.php?id=02-001&gl=912
 

Offline Bored chemist

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« Reply #6 on: 07/10/2007 14:44:44 »
"Air, even under pressure, is transparent - to see something, you need impurities in the air."
Does water, always a constituent of air, count as an impurity? It's frequently visible.
 

Offline Alandriel

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« Reply #7 on: 08/10/2007 15:04:37 »
I'm still not convinced they're real....................
 

another_someone

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« Reply #8 on: 08/10/2007 17:22:47 »
"Air, even under pressure, is transparent - to see something, you need impurities in the air."
Does water, always a constituent of air, count as an impurity? It's frequently visible.

It was certainly my intention to include water, at least in its frozen form, in my term 'impurities'.

Water, in its gaseous form, as far as I am aware is never visible in air (although I am assuming that the changes in pressure within the shock waves may well precipitate water from its gaseous to its frozen form).
 

Offline Bored chemist

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« Reply #9 on: 08/10/2007 20:51:49 »
"Water, in its gaseous form, as far as I am aware is never visible in air "
So? What's wrong with fog or clouds?
My money would be on the liquid form rather than ice.
 

Offline Alandriel

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« Reply #10 on: 08/10/2007 21:22:26 »
ohhh...... I can take bets!  ;D

10 to 5 it's liquid
20 to 7 it's ice

100-5 this is real

1-1 I need to go to bed!

just ignore me..... see ya tomorrow!

YAY!  :o look at that time stamp - DEFINITELY BED TIME..... this is eeeeerie
 

another_someone

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« Reply #11 on: 08/10/2007 21:34:48 »
"Water, in its gaseous form, as far as I am aware is never visible in air "
So? What's wrong with fog or clouds?
My money would be on the liquid form rather than ice.


Fog and clouds are not gaseous - they are liquid or solid suspensions.

I would not discount liquid droplets, but it does look a bit too bright to my mind for that, but that is by no means to say it is not that.
 

another_someone

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« Reply #12 on: 08/10/2007 21:36:28 »
YAY!  :o look at that time stamp - DEFINITELY BED TIME..... this is eeeeerie

You don't expect to believe the time stamps on the forum, do you (I suppose they would do alright for Switzerland).
 

Offline Alandriel

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« Reply #13 on: 08/10/2007 21:41:17 »

I'm an early bird ......
10pm is usually tops as I read for a good hour and then get up at the crack of dawn....
The time stamp just threw me because of the near 22:22:22

nighty night  :)


 

Offline DoctorBeaver

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« Reply #14 on: 08/10/2007 22:09:54 »

I'm an early bird ......
10pm is usually tops as I read for a good hour and then get up at the crack of dawn....
The time stamp just threw me because of the near 22:22:22

nighty night  :)




3 Desmonds - Tutu Tutu Tutu!  :D
 

paul.fr

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Sound barrier - pictures?!?
« Reply #15 on: 09/10/2007 03:51:10 »
Ok, what about this: a type of vapour trail, but not a conventional one. I tried to combine most ideas and get this: there are water vapour molecules present as the plane goes supersonic, the water and other molecules are under high pressure and the air is humid, thus forming a 'vapour trail'
 

another_someone

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« Reply #16 on: 09/10/2007 04:29:41 »
As I rather suspected, it is more due to low pressure than to high pressure, but otherwise you are about correct.

http://en.wikipedia.org/wiki/Transonic#Interesting_facts
Quote
At transonic speeds intense low-pressure areas form at various points around an aircraft. If conditions are right (i.e. high humidity) visible clouds will form in these low-pressure areas as shown in the illustration; these are called Prandtl-Glauert singularities. These clouds remain with the aircraft as it travels. It is not necessary for the aircraft as a whole to reach supersonic speeds for these clouds to form.

http://en.wikipedia.org/wiki/Prandtl-Glauert_singularity
Quote
The Prandtl-Glauert singularity (sometimes referred to as a "vapor cone"), is the point at which a sudden drop in air pressure occurs, and is generally accepted as the cause of the visible condensation cloud that often surrounds an aircraft travelling at transonic speeds, though there remains some debate. It is an example of a mathematical singularity in aerodynamics.

One view of this phenomenon is that it exhibits the effect of compressibility and the so-called "N-wave". The N-wave is the time variant pressure profile seen by a static observer as a sonic compression wave passes. The overall three-dimensional shock wave is in the form of a cone with its apex at the supersonic aircraft. This wave follows the aircraft. The pressure profile of the wave is composed of a leading compression component (the initial upward stroke of the "N"), followed by a pressure descent forming a rarefaction of the air (the downward diagonal of the "N"), followed by a return to the normal ambient pressure (the final upward stroke of the "N"). The rarefaction may be thought of as the "rebounding" of the compression due to inertial effects.

These condensation clouds, also known as "shock-collars" or "shock eggs," are frequently seen during space shuttle launches around 25 to 33 seconds after launch when the vehicle passes through the area of maximum dynamic air pressure, or max Q. These effects are also visible in archival footage of some nuclear tests. The condensation marks the approximate location of the shock wave.

Since heat does not leave the affected air mass, this change of pressure is adiabatic, with an associated change of temperature. In humid air, the drop in temperature in the most rarefied portion of the shock wave (close to the aircraft) can bring the air temperature below its dew point, at which moisture condenses to form a visible cloud of microscopic water droplets. Since the pressure effect of the wave is reduced by its expansion (the same pressure effect is spread over a larger radius), the vapor effect also has a limited radius. Such vapor can also be seen in low pressure regions during high–g subsonic maneuvers in humid conditions.

Prandtl-Glauert singularity effects can be readily observed on a humid day by successfully cracking a whip. A visible cloud is produced at the point where the tip of the whip goes transonic.

Notes
    1. It is important to recognize that the pressure profile rise-drop-rise is only figuratively described by an "N" and, indeed, it is better described as a "stylized-N" since the profile takes place within an ambient pressure context with pressure starting from, and returning to, the same ambient point afterward. Therefore, the "free-tips" on the end of the "N", relative to the centre of the diagonal do not begin as low, nor end as high, as is implied by the normal shape of the letter N.

« Last Edit: 09/10/2007 04:33:36 by another_someone »
 

paul.fr

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« Reply #17 on: 09/10/2007 04:44:01 »
As I rather suspected, it is more due to low pressure than to high pressure, but otherwise you are about correct.
Quote
no way! Ok, not wishing to go against the guys and gals at wiki. But, could there haue been a high pressure system and one of the actions of the planes speed was or is to cause a localised low pressure?
 

another_someone

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« Reply #18 on: 09/10/2007 04:57:33 »
As I rather suspected, it is more due to low pressure than to high pressure, but otherwise you are about correct.
no way! Ok, not wishing to go against the guys and gals at wiki. But, could there haue been a high pressure system and one of the actions of the planes speed was or is to cause a localised low pressure?

I think you misunderstand - it is all about local pressure around the plane - the vapour cloud is condensed in the low pressure region just behind the shock wave.
 

paul.fr

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« Reply #19 on: 09/10/2007 05:22:52 »
To be honest george, i have not yet read the wiki article, something that long on a 1.5 inch screen is too much for me. I was just going off where you said low pressure and i had this big about high pressure. The confusion is mine.
 

Offline Alandriel

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« Reply #20 on: 09/10/2007 12:03:29 »
Prandtl-Glauert singularity

Now how cool is that???

 [8D] [8D] [8D]

Thanks George  ;D
you timestamp on that post..... Did this keep you up all night????



***jumps off the fence***




Now just immagine me saying very casually over coffee next time I see my friend Prandtl-Glauert singularity


Gosh I really ought to take some course work.....

 ;D ;D ;D
« Last Edit: 09/10/2007 12:07:36 by Alandriel »
 

another_someone

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« Reply #21 on: 09/10/2007 14:23:33 »
you timestamp on that post..... Did this keep you up all night????

Is the small lettering to make sure I am awake when I answer you? :)

I am your opposite, more the owl (maybe even a bat) than the lark - and I was up doing other things - but yes, up later than I wanted.
 

Offline Alandriel

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« Reply #22 on: 09/10/2007 14:51:57 »
Quote from: George
Is the small lettering to make sure I am awake when I answer you?

Never thought of it that way - but why not?!?!? LOL
No, that's how I whisper......

You're the bat man, aye?


Wonder if I'll see ya tonight on my bat walk in Hyde Park



gotta love bats........














and snow owls#











.................. and right back on topic..................




 ;D

 

Offline iko

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« Reply #23 on: 09/10/2007 18:15:23 »
...more supersonic pics here!

 

Offline techmind

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Sound barrier - pictures?!?
« Reply #24 on: 25/10/2007 13:55:23 »
As I rather suspected, it is more due to low pressure than to high pressure, but otherwise you are about correct.
http://en.wikipedia.org/wiki/Prandtl-Glauert_singularity

Quote
Prandtl-Glauert singularity effects can be readily observed on a humid day by successfully cracking a whip. A visible cloud is produced at the point where the tip of the whip goes transonic.
Looks like something to try on one of those steamy-kitchen days...  true kitchen-science  :)
 

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« Reply #24 on: 25/10/2007 13:55:23 »

 

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