Mysterious Sound Waves Can Destroy Rockets 193
Ponca City, We love you writes "Scientists believe that powerful and unstable sound waves, created by energy supplied by the combustion process, were the cause of rocket failures in several US and Russian rockets. They have also observed these mysterious oscillations in other propulsion and power-generating systems such as missiles and gas turbines. Now, researchers at the Georgia Institute of Technology have developed a liquid rocket engine simulator and imaging techniques to help demystify the cause of these explosive sound waves and bring scientists a little closer to being able to understand and prevent them. The team was able to clearly demonstrate that the phenomenon manifests itself in the form of spinning acoustic waves that gain destructive power as they rotate around the rocket's combustion chamber at a rate of 5,000 revolutions per second. Researchers developed a low-pressure combustor to simulate larger rocket engines then used a very-high-speed camera with fiber optic probes to observe the formation and behavior of excited spinning sound waves within the engine. 'This is a very troublesome phenomenon in rockets,' said Professor Ben Zinn. 'These spinning acoustic oscillations destroy engines without anyone fully understanding how these waves are formed. Visualizing this phenomenon brings us a step closer to understanding it.'"
Brown noise (Score:5, Funny)
Re:Brown noise (Score:4, Funny)
Re:Brown noise (Score:4, Funny)
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This was just something me and my friends say now and then "Rocket Surgery" and "Brain Science".
However, I will take the credit!
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Anyone want to try an experiment? This page - http://www.learner.org/jnorth/tm/spring/PicturingSound.html [learner.org] has an audio file of a 5,000 Hz signal. See if you either explode like these rocket or crap your pants.
http://www.learner.org/jnorth/sounds/Tone5000Hz.wav [learner.org]
Layne
Re:Harmonics (Score:4, Interesting)
It generally takes about 110dB to shatter a wine glass via oscillation, but it isn't direct exposure to the pressure that causes that.
Depending on the quality, glass will begin to shatter above 160-165 dB, independant of its resonant frequency. Of course, if you are dealing with flexible glass, that value will increase.
It is quite possible to have a sound wave impact with enough force on a specific area in a rocket engine to cause enough fatigue which will result in a failure without actually resonating.
So why is this news? Because depending on the atmospheric pressure, once you get above 194 dB, the soundwave becomes distorted, it would be difficult enough to model a soundwave in a motionless, inactive engine, but I can't even begin to comprehend how complex the modeling must be of an engine that is generating sound waves in excess of 200dB in such an extreme and dynamic environment.
That they are able to model this is amazing.
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Good news! (Score:5, Funny)
Re:Good news! (Score:4, Funny)
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You may now resume saying "Well, this isn't rocket science"
Except that this is rocket science.
Re:Good news! (Score:5, Insightful)
But shockwave instability in rocket propulsion systems has been a known problem since the very beginning of rocketry. They've been solving it repeatedly for decades. Heck, the Saturn V's F1 engine had it bad in early designs. Solving the F1's shockwave problem required significant innovations in testing methods and tools, and in fuel injection techniques, but solved it was.
The only thing going on today is the same thing that's been going recently in a lot of fields from building architecture to aerodynamics: the replacement of empirical trial-and-error problem-solving methods with highly complex mathematically-driven computer simulation methods.
Indeed, this advancement of the state of the art will make rocket science easier, since it allows researchers to model different designs in much greater detail, without having to physically build them.
I've been a member of slashdot for some time (Score:5, Funny)
Vibrator?? (Score:2, Funny)
Re:Vibrator?? (Score:5, Funny)
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What the gp asked and what the parent referred to. [uncyclopedia.org]
Re:Vibrator?? (Score:4, Funny)
>>of course. we've got lots of pictures. =D
Yeah, and I know all about womens emotions and stuff. Like, chicks HATE it when you call them broads.
I can finally be of use to science (Score:5, Funny)
Re:I can finally be of use to science (Score:5, Funny)
Oh great, Mr. Goatse himself is now posting on slashdot.
Re:I can finally be of use to science (Score:5, Funny)
Thats impossible. In order to get a good sound out of that it'd have to be a bit tighter and able to make a good PHHHHHHBBBBBTTT sound. The way Mr. Goatse is now it would just kind of go phooooo. Even then I doubt if there is enough of a seal left to keep it from leaking out long enough to build up sufficient volume and pressure to do anything noticable.
Re:I can finally be of use to science (Score:5, Funny)
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phoooooo.
What TFA leaves out (Score:3, Funny)
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Defense System? (Score:4, Insightful)
Re:Defense System? (Score:5, Funny)
Moha deeb.... rocket go boom
Re:Defense System? (Score:5, Insightful)
No. We're talking about pressure waves inside the engine, at pressures measured in tens or hundreds of psi, that resonate with the injector to build power -- think about blowing across the top of a beer bottle. The small power input from your breath induces a higher power oscillation. Same effect, where the bottle is replaced by the combustion chamber and your breath by the injectors. Except the power involved is a hundred million times higher (maybe more, I didn't do the math very carefully).
These waves can't be set up unless the engine will support them, and if it will then they'll happen on their own. If you could deliver that much energy to the engine remotely, you could just as easily destroy the rocket. It's the *resonance* that's the problem, not the fact that there's a crapload of sound energy available.
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Re:Defense System? (Score:5, Interesting)
The laser beam is way more feasible, even if you ignore considerations of range. Not to mention that when a liquid-fueled military rocket is operating, it's going to be either over the horizon or in vacuum -- we're not talking about small tactical missiles here.
We're talking about loud sounds here -- and not just a little bit loud. 1 pascal of pressure wave is 94dB SPL -- a fairly loud sound. 1 psi is 6894 pascals; we're talking about many psi of pressure variation. A 10 psi wave would be 190dB. That's not just loud enough to cause hearing damage; that's well past loud enough to knock over buildings. Overpressure from large bombs is less than that at the edge of the blast radius.
It should be obvious why that's destructive when it happens inside a rocket chamber, especially since oscillations like that tend to start small, grow *rapidly*, and not stop growing until something breaks. It should also be obvious why you won't be able to create such a wave via external influence unless the chamber can already resonate in that mode. When developing the F1 (Saturn V main engine) NASA had trouble with instability; in order to see whether the engine was barely stable or had plenty of margin, they had to find techniques to induce these waves. What they developed, and still use today, is a set of techniques for putting an explosive charge *inside* the engine, bringing the engine up to normal operating conditions (making the charge survive this is nontrivial), and *then* detonating it to see how the engine responded.
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Sutton discusses that resonant mode (spinning tangential) briefly in Rocket Propulsion Elements (pg 353, 7th ed). There are plenty of more detailed discussions of combustion instability in general elsewhere in the literature. There are a variety of other resonant modes as well, this just happens to be the one the researchers looked at.
You can indeed add features to the chamber to de-tune it. It's anything but simple, though, and is mostly trial and error at present. Making the features not burn up is
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That sounds WAY more easy than star wars, as long as you arrange it all before they launch.
Actually, maybe there isn't as much in it as I thought.
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In space, no one can hear you scream.
-JS
If you play them backwards (Score:4, Funny)
Jimi at Berkeley (Score:2)
The Captain has known since 1986 that sound waves, particularly the very potent tones of Jimi at Berkeley, can destroy oncoming rockets.
Reference: Riders of the Storm [imdb.com]
And then... (Score:3, Funny)
Summary is a bit off (Score:5, Informative)
The new result here isn't acoustic instabilities; those have been known for a long time. The interesting result is a new set of imaging techniques that give a better understanding of *why* they occur, rather than simply observing on pressure traces that they *do* occur. After a bit more research, this may turn into techniques to more reliably avoid them in the design stage, rather than having to go through various tweaks on the injector / combustion chamber to remove them should they appear.
This is very cool work. Of course, it's rocket science, not rocket engineering, so it's unlikely to impact new designs for several years yet.
Re:Summary is a bit off (Score:4, Interesting)
Or I could be full of crap, which is also a distinct possibility.
Re:Summary is a bit off (Score:5, Informative)
No, you're on the right track, but not quite there. Computational techniques are only barely able to simulate rocket chambers well; combustion dynamics are complex and not well understood. That's a large part of what makes this work interesting (the other part being the imaging techniques to actually photograph the waves).
The problem isn't actually the chamber or nozzle walls resonating, it's the acoustic cavity -- exactly analogous to an organ pipe. There are a variety of techniques used to de-tune the resonance modes. (It also happens in the chamber, not the nozzle -- gas in the expansion portion of the nozzle is locally supersonic, so sound can't propagate backwards, which means no resonance.) For example, the SSME has some of the injectors protruding further into the chamber than others, creating interruptions in the flat surface of the injector face. There exist other techniques, and some google searching will turn up some. Also, playing with the metals in the chamber wall is probably right out -- they're basically already decided by thermal considerations, and high performance engines almost universally use copper.
Historically, the design process has involved experienced engineers, rules of thumb, and lots of testing. Computer models will help, but they'll never really replace the "lots of testing" stage. At least for small engines (up to several thousand pounds of thrust), it's cheaper, easier, and more accurate to just build the thing.
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Re:Summary is a bit off (Score:5, Informative)
Titanium may melt at 1900K, but rocket chambers operate in the realm of 2500-3500K. They have to be cooled, and copper is the material of choice for the same reason it makes good CPU heat sinks -- excellent thermal conductivity. Some older thrust chambers were made of steel (WAC Corporal, iirc), and it works at low chamber pressures (less heat flux), but it doesn't work as well and there are corrosion issues in storage. As performance increases and chamber pressures rise, metals other than copper look less and less appealing.
Some nozzles are uncooled in the aft portion (as the gas expands and accelerates, it cools down, so the environment gets easier to handle). The Kestrel engine used in the Falcon 1 upper stage, for example, has a radiatively cooled Niobium nozzle. Titanium has been used, but Niobium and a few others tend to perform better in that environment -- the combination of hot reactive gases is hard to handle.
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"I cannot be played on [rocket engine] X".
Everything has resonant frequencies. Most phenomena do not input enough energy at those frequencies to cause damage to arbitrary man-made devices, but when they do - Watch out Tacoma Narrows.
In the case of a rocket engine, you have a LOT
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Tacoma narrows had very little to do with resonance. The problem there was that a small amount of torsion changed the aerodynamic profile of the bridge so that it would pick up more energy from the wind, which increased the amount of torsion, which changed the aerodynamic profile even more, which caused the bridge to p
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Mr. Tortoise? Is that you? Now that you've messed up Mr. Crab's hi-fis, you've decided to screw up his rockets too?
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Especially considering the fact that major new liquid-fueled rocket engines are designed at a rate of about one per decade...
Dune? (Score:2)
This has got to be joke (Score:5, Funny)
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Weapon (Score:2, Interesting)
Nigel Tufnel Explains (Score:2, Funny)
Experiment IV (Score:2)
All they wanted
Was a sound that could kill someone
From a distance.
Instead, it killed the rockets!
Powerful sound waves? (Score:4, Funny)
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Turn it inside out. (Score:5, Interesting)
Re:Turn it inside out. (Score:4, Interesting)
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http://en.wikipedia.org/wiki/Image:Aerospikeprinciplediagram.gif [wikipedia.org]
In the linked illustration on the right, look along the top edge of the aerospike, where the flames are coming from. All of the little canisters along both edges (where the flames come
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Of course, this was long ago, and I was at the bottom level of the work, and only worked a very short time on that.
Pogo Oscillations (Score:4, Interesting)
http://en.wikipedia.org/wiki/Pogo_oscillations [wikipedia.org]
Re:Pogo Oscillations (Score:4, Informative)
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The reference I read indicated that there was a pogo fault on the center engine on the first st
hmm (Score:2)
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Addicted to bass... (Score:3, Funny)
Sonic Tools (Score:3, Funny)
How simple can this be? (Score:2)
What's so hard about that?
Rocket science.... Hrumph!
Ithorians (Score:2)
More technology to misuse (Score:2)
Combustion instability is an old problem (Score:4, Interesting)
Combustion instability is an old problem with rocket engines. The Saturn V main engine had serious combustion instability problems, which were fixed by trial and error testing. The Apollo booster people had to resort to setting off small bombs inside engines on test stands to induce instability, then trying different patterns of holes in the plates the distributed fuel to find a stable configuration.
The SR-71 engine had serious combustion instability. That, too, was fixed with something of a hack, an automated "sympathetic unstart" system which, when one engine had a stall, would stall the other one, then restart both.
Better simulation tools in that area can't hurt. Not many big supersonic engines are designed any more. As Scott Crossfield pointed out just before he died a few years ago, every aircraft that went significantly over Mach 3 is now in a museum.
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As Scott Crossfield pointed out just before he died a few years ago, every aircraft that went significantly over Mach 3 is now in a museum.
There is little if any need now for piloted aircraft that can reach those speeds. Even as early as the 1960s, it was clear to everyone involved that guided missiles would obviate the need for supersonic manned bombers and other similar weapons systems. The mach 3+ reconnaissance aircraft survived somewhat longer in the form of the aforementioned SR-71 but even that eventually fell by the wayside as satellites and now remote piloted (and cheap) drones have replaced it too. The military value of tremendous s
Coriolis Effect in Vortex Combustion (Score:5, Interesting)
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This racetrack instability is actually a well known problem with annular combustion chambers such as those used with the toroidal aerospike engine [wikipedia.org]. One of the main virtues of vortex engines, like Orbital Technologies [california...hority.org] or the ultracentrifugal one [geocities.com] invented by Roger Gregory [wikipedia.org] and myself, is that the coriolis effect [wikipedia.org] distorts the wave front sending it into the wall of the combustion chamber. In theory, at least, this should disrupt the resonance enough to prevent destructive standing waves.
Experiments have not been conducted to test this theory yet to the best of my knowledge.
Pretty much any adaptation which broke the circularity of any of the problem designs would work, no? Graphite vanes, a la V2 steering, only farther up the bell. Grooves down the length of an aerospike. Injectors in the bell which shoot the fuel/oxidizer at alternating angles with pseudo-randomly (slightly) different pressures. Or even building in just enough pogo oscillation to disrupt it. Of course these are just hacks on the present designs, not new designs which address the problem. The hybrids I've see
Finally, vindication! (Score:2)
Shuttle launches and Gatornationals... (Score:2)
From about 7 miles away, that thing literally "shakes the sky".
I also like auto racing. The Gatornationals are drag races which include those Nitrous burning funny cars and dragsters. You can get 20 feet away from them down by the fence when they launch. Now those things do not just "shake the sky" --- THE SHAKE YOU. It feels like the dang time-space continuum is being warped and you are too. It is absolutely worth the price of admi
This is a slashdot story! (Score:2)
Reading this story and the linked article at Georgia Tech made me flash back about 10 years to when I first discovered Slashdot.
Great article, classic Slashdot!
Why stop the waves? (Score:2)
Maybe in addition to finding a way to stop the pressure waves they should also be looking for a way to enhance them and direct them... preferably in a way that creates additional propulsion or possibly a standing wave of some sort.... would be really cool if this led to a method of hovering... the militar
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http://www.rastko.org.yu/rastko/delo/10896 [rastko.org.yu]
[Nikola Tesla:] "I was experimenting with vibrations. I had one of my machines going and I wanted to see if I could get it in tune with the vibration of the building. I put it up notch after notch. There was a peculiar cracking sound.
"I asked my assistants where did the sound come from. They did not know. I put the machine up a few more notches. There was a louder cracking sound. I knew I was approaching the v
More importantly (Score:2)
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Somthing Wrong Here. was Re:Nothing new here (Score:5, Informative)
Ok, before parent gets any farther this has to be de-bunked. Sound waves did not destroy the bridge. A sound wave, in any medium consists of a compression and a rarifraction ., that is a leading pressure wave followed by a area of lower pressure that propagate in a known fashion. The intensity of a sound wave obeys the inverse square law.
What happened to the Tacoma Narrows Bride was caused be an error in aerodynamic calculations on the part of the design engineer. Air passing around the bridge deck acted exactly like air does when presented with a crude airfoil, it formed an area of low pressure leeward of the bridge deck and a low pressure area leeward and below the bridge deck. Th resulting high pressure and low pressure vectors imparted a twisting moment to the bridge deck.
The twisting moment was resisted by the torsional rigidity of the bridge deck. This caused the deck to twist to and build torsional tension. The twisting caused the aerodynamic profile of the bridge deck to change. The resulting change allowed the bridge deck to revert back to its original shape and aerodynamic profile, rinse and repeat. Thus the repeated twisting caused enough of the riveted and bolted joints to fail which led to a cascade failure as the remaining joints failed under the bridges weight and twisting motion.
This was not "low frequency sound waves" although the structures oscillations did cause some very low frequency sounds waves, it was destroyed by nothing more then bad aerodynamics.
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"As God as is my witness, I thought bridges could fly" -- The Engineer who designed the Tacoma Narrows Bridge
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The wave argument is that the "rinse and repeat" frequency just happened to be the same as the resonant frequency [wikipedia.org] of the main bridge cables, this took the areodynamicly induced twisting motion and turned it into opposing waves of maximum amplitute along the two main cables. If yo
Broken link (Score:2)
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The point is that the problems don't end here - the twisting of the deck gives the wind a larger angle of attack, which leads to more twisting
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I accept that. What I don't understand is how does that mechanisim rule out amplification by resonance, what makes you so sure?
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The natural frequency (the one at which it is in resonance) can be determined, and it was different from the frequency the bridge actually oscillated at before is collapsed. The brigde may not have had enough damping at the latter frequency, but it wasn't the frequency at which it would have been in resonance.
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I don't think changing the natural frequency would have helped since the frequency of the forces would have followed. Most of the time engineers observe resonant frequencies where the force frequency is not a function of the natural frequency of the object(like a building in an earthquake). The force frequency just ha
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Layne
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I'm wondering if the waves are just something related to how the energy goes out at such high pressures and it being a bit opposite in how the soda bottle "vortex generators" work. Pressure is high enough so that all the fluid flows out axially instead of rotating around the axis to some degree, but thes
Re:"Strange wave phenomenon" = resonance (Score:4, Informative)
Pogo, pump-related oscillations, and plumbing related oscillations are all low frequency (tens of Hz, sometimes less). These are acoustic modes internal to the chamber, in the kHz range. They're very distinct phenomenon, with distinct causes and distinct solutions. They're still a 50 year old problem with 50 year old techniques to solve them, but they're by no means understood in any meaningful sense -- the current technique mostly involves testing the engine and then tweaking it until they go away.
The new and interesting work here is the modelling, combined with the photography techniques. Seeing pressure waves at the injector face through the chamber full of flame is not trivial.
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And so the old question foes, "If a tree falls in the forest and there is no one there to hear it, does it make a noise?
Well by the definition of sound there are three components:
Hence the phrase, "In space no one can hear you scream.". Now that was a movie, but it is never the less true. We have all seen the experiment where you take an electric bell, place it in a vacuum chamber. As the air is pumped out the, softer the sound of the bell gets unti
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If you are an English major and a tree falls in the forest and there is no one there to hear it, there is no sound.
Physicists define sound as compression waves traveling through a medium, like air. So a Physicist does not need an observer for the sound to exist. as long as the falling tree starts a series of compression waves in the compressible media around it (air, water, ground) there is sound.
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Dictionary.com says the definition of "sound":
Def. 2. mechanical vibrations transmitted through an elastic medium, traveling in air at a speed of approximately 1087 ft. (331 m) per second at sea level.
Merriam-Webster, "sound":
1.c. mechanical radiant energy that is transmitted by longitudinal pressure waves in a material medium (as air) and is the objective cause of hearing
OK, then what about the word "noise":
Dictionary.com again, "noise":
Def. 2. a sound of any kind
Merriam-Webster, "noise":
Hmmm... the closest definition is:
2.b. any sound that is undesired or interferes with one's hearing of something
So, no mention of a detector other than only on the Merriam-Webster definition of "noise" might a detector be needed.... although that is subjective on whether you desire the sound of a tree falling. Otherwise