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Mysterious Sound Waves Can Destroy Rockets 193

Posted by Soulskill
from the scientists-get-the-best-toys dept.
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.'"
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Mysterious Sound Waves Can Destroy Rockets

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  • Brown noise (Score:5, Funny)

    by rubies (962985) on Thursday April 10, 2008 @11:15PM (#23032416)
    It makes rocket scientists crap their pants!
    • by menkhaura (103150) <espinafre@gmail.com> on Thursday April 10, 2008 @11:23PM (#23032466) Homepage
      Bah, rocket science isn't brain surgery!
    • by creimer (824291)
      Those sound waves usually make people take cover too.
  • Good news! (Score:5, Funny)

    by bluephone (200451) <greyNO@SPAMburntelectrons.org> on Thursday April 10, 2008 @11:17PM (#23032430) Homepage Journal
    This means rocket science is once again hard. You may now resume saying "Well, this isn't rocket science" until they solve this.
    • by fractoid (1076465) on Thursday April 10, 2008 @11:52PM (#23032664) Homepage
      Bah, this isn't hard. These rockets are just getting speed wobbles, any 8-year-old boy with a bike will be able to tell you all about them!
    • You may now resume saying "Well, this isn't rocket science"

      Except that this is rocket science.

    • Re:Good news! (Score:5, Insightful)

      by susano_otter (123650) on Friday April 11, 2008 @12:14PM (#23037494) Homepage

      This means rocket science is once again hard. You may now resume saying "Well, this isn't rocket science" until they solve this.

      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.
  • by JeanBaptiste (537955) on Thursday April 10, 2008 @11:17PM (#23032434)
    and the subject line for this article has finally convinced me that cowboy neal is in fact art bell.
  • Vibrator?? (Score:2, Funny)

    by AmigaHeretic (991368)
    Is that a rocket in your pocket? Finally I could satisfy a woman! :(

  • I wonder if they'd be interested in analyzing the smoking ruins of at least 5 toilet bowls I have personally destroyed with mysterious oscillating rocket powered sound waves.
  • by garett_spencley (193892) on Thursday April 10, 2008 @11:19PM (#23032452) Journal
    When analyzing the acoustic oscillations scientists discovered something quite striking. The sine wave was exactly identical to the master recording of Britney Spears' "Hit Me Baby One More Time".
  • Defense System? (Score:4, Insightful)

    by BountyX (1227176) on Thursday April 10, 2008 @11:26PM (#23032498)
    Could be implemented in a way to defend against rocket\missle attacks? Possibly in a better way than Star Wars program.
    • by zappepcs (820751) on Thursday April 10, 2008 @11:32PM (#23032538) Journal
      Ever watch the movie Dune?

      Moha deeb.... rocket go boom
    • Re:Defense System? (Score:5, Insightful)

      by evanbd (210358) on Thursday April 10, 2008 @11:40PM (#23032600)

      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.

      • by RKBA (622932)
        So they need to find a shape for the combustion chamber/nozzle that has no single large fundamental resonance frequency, but without sacrificing too much thrust efficiency. It will be interesting to see what sort of shape, or baffling system, they devise. Maybe they could use some of the expertise from the manufacturers of firearm sound suppressors [wikipedia.org] who face similar problems, though less serious and demanding. Although resonance isn't the problem firearm suppressors are designed to address, they do considera
    • Re: (Score:2, Insightful)

      by Hojima (1228978)
      Almost instantly you can see that it would be very impractical to use sound to destroy rockets. Unless you blast the sound waves constantly, you wont be able to destroy the rockets since they travel much faster than sound (that and air is a terrible medium to transfer the waves through with the Doppler effect hindering it, so they'll never reach the missiles with enough strength). Lasers are still tricky, but there wont be a better alternative to them in the future, when their strength and our tracking syst
    • by Johnno74 (252399)

      Could be implemented in a way to defend against rocket\missle attacks? Possibly in a better way than Star Wars program.
      Yeah, all you'd need to do is mount an extremely hardy, remote-controled loudspeaker inside the combustion chamber of every rocket your enemy had.

      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.

    • by jstott (212041)

      Could be implemented in a way to defend against rocket\missle attacks? Possibly in a better way than Star Wars program.

      In space, no one can hear you scream.

      -JS

  • by xs650 (741277) on Thursday April 10, 2008 @11:34PM (#23032548)
    If you record them and play them backwards they will install Vista on your computer.
  • 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)

    by adona1 (1078711) on Thursday April 10, 2008 @11:36PM (#23032564)
    Dr No will fish them out of the water and pass the rockets on to SMERSH....I don't like the sound of that!
  • Summary is a bit off (Score:5, Informative)

    by evanbd (210358) on Thursday April 10, 2008 @11:36PM (#23032568)

    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.

    • by Nefarious Wheel (628136) on Thursday April 10, 2008 @11:55PM (#23032680) Journal
      A problem with dealing with acoustic resonance is just how to manufacture the rocket nozzle to avoid the buildup of these dangerous resonances. Modelling them is the first step, but how can you build the nozzle with sufficient strength while building in structure to interrupt the phase of the wave repeats? Experimentation is a lot cheaper when you can simulate the results. I could imagine moving to non-round shapes might solve the problem, or heterogenious structures - possibly by introduction of dissimilar materials in the bell, perhaps a strapped interspersion of titanium and stainless? I wonder how difficult that could be to model.

      Or I could be full of crap, which is also a distinct possibility.

      • by evanbd (210358) on Friday April 11, 2008 @01:04AM (#23032968)

        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.

    • by pla (258480)
      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.

      "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
      • by Ihlosi (895663)
        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.

        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

      • by sconeu (64226)
        "I cannot be played on [rocket engine] X".

        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?
      • by evanbd (210358)
        The problem is one of Q factor. Resonant modes in an engine *will* be excited -- engines tend to have fairly distinctive character when you look at the FFT of the chamber pressure trace (a fancy way of saying engines have their own unique sound). If the resonance has a high Q factor, then the modest input power available at that frequency will build rapidly, and couple into the combustion process or injector and gain even more energy. If the Q factor is low, then it will only show up as a small peak abov
    • by XNormal (8617)
      > 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.

      Especially considering the fact that major new liquid-fueled rocket engines are designed at a rate of about one per decade...
  • by B5_geek (638928)
    House Atreides was not available for comment.
  • by Riktov (632) on Thursday April 10, 2008 @11:41PM (#23032608) Journal
    Come on, an expert on rocket fuel technology named Professor Ben Zinn [reference.com]?
  • Weapon (Score:2, Interesting)

    by MrGHemp (189288)
    I can't help but wonder if understanding this won't lead to some powerful weapons... think about it a sonic cannon, that might make some interesting CNN coverage during war time.
  • *Blank stare* - "These go to eleven."
  • They told us
    All they wanted
    Was a sound that could kill someone
    From a distance.

    Instead, it killed the rockets!
  • by gmuslera (3436) on Friday April 11, 2008 @12:01AM (#23032712) Homepage Journal
    Heavy Metal can destroy even rockets now.
  • Turn it inside out. (Score:5, Interesting)

    by camperdave (969942) on Friday April 11, 2008 @12:08AM (#23032748) Journal
    Rocket engines typically have a round cross section, which, if it doesn't aid the production of these circular waves, probably does little to dampen them. I wonder if the "inside out" design of a linear aerospike engine [google.com] suffers from the same problem.
    • by evanbd (210358) on Friday April 11, 2008 @01:06AM (#23032980)
      Aerospike engines still have an enclosed chamber; it's only the nozzle that's been changed. The chamber is where the problems occur, not the nozzle. The odd chamber shapes certainly make things complicated, but I have no idea whether they hurt or help overall. The usual technique to get rid of these involves various ways to de-tune the engine -- for example, some of the SSME injectors protrude deeper into the chamber to interrupt the otherwise flat injector face.
      • Aerospikes have enclosed chambers? I don't recall seeing one on the test videos, and as far as I recall the aerospike uses outside air pressure as the bell. Having just read http://en.wikipedia.org/wiki/Aerospike_engine [wikipedia.org], it seems to confirm what I thought. The included illustration doesn't depict a chamber either.
        • Re: (Score:3, Informative)

          by icebrain (944107)
          It does depict them, you just aren't looking hard enough. On a traditonal rocket engine, the chamber is a bulbed or cylindrical chamber above the nozzle. It narrows down, then expands into a bell shape to allow the combusted hot gasses to expand and accelerate.

          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
    • Re: (Score:3, Interesting)

      by MickLinux (579158)
      I seem to remember back in 1987/8, working at VA Tech on a project where they were considering scalloped semicircles all around the edge of the cross section. It seems to me that the purpose was to get a more even burn (read, reduce some of the acoustic/shock wave artifacts of the combustion).

      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)

    by orospakr (715849) on Friday April 11, 2008 @12:19AM (#23032808) Homepage
    This phenomenon sounds very similar to Pogo Oscillations, which incidentally caused the engine 5 shutdown on the Apollo 13 Saturn V.

      http://en.wikipedia.org/wiki/Pogo_oscillations [wikipedia.org]
    • Re:Pogo Oscillations (Score:4, Informative)

      by evanbd (210358) on Friday April 11, 2008 @01:17AM (#23033030)
      Similar, but different. Both are oscillations, but pogo is characterized by low frequency variations in chamber pressure coupling through the thrust structure and into the propellant feed system (and from there back to the chamber pressure). These are high frequency (kHz, no tens of Hz) acoustic modes, contained entirely within the chamber. They're much harder simulate and much harder to get rid of, and much less well understood. They couple from local chamber pressure to the injectors, and operate much like an organ pipe.
    • by TeknoHog (164938)
      I presume the frequency of these oscillations is measured as "pogomips".
  • Doesn't everything have a frequency at which it breaks? I mean, human rib cages, crystal glasses have been known to break with just the right tone. In the case of a former engine of mine (non-rocket), it was right around 133Hz (8000rpm/60seconds=133 Cycles per second).
    • by Detritus (11846)
      Not really. It depends on the material and shape. If you look at objects as oscillators. an important factor is the Q (quality factor [wikipedia.org]). That determines how quickly the object loses energy when excited at its resonant frequency. A bell cast from brass has a high Q when compared to a bell made from fiberglass. You need a high Q to accumulate and store energy. An object with a low Q just quickly dissipates the energy as heat.
  • by roxtafari (1256480) * on Friday April 11, 2008 @12:46AM (#23032910)
    Looks like an audio engineering issue. While not being a rocket engineer myself, I assume the combustion chamber is somewhat symmetrical. It is likely acting as a resonance chamber and increasing the amplitude of the soundwave to the point of physical damage. I shattered the rear window in my '96 Camaro twice with a 1200W Fosgate and a single 10" bazooka tube. Tell NASA to crack the window when they turn up the bass!
  • Sonic Tools (Score:3, Funny)

    by Professr3 (670356) on Friday April 11, 2008 @12:58AM (#23032938)
    So THAT'S how the Doctor's screwdriver works...
  • All you've got to do is to wrap the rocket in sound deadening materials - or negate the sounds by amplifying the same sound out of phase.
    What's so hard about that?
    Rocket science.... Hrumph!
  • Four throats. Very powerful.
  • "excited spinning sound waves" sounds like something which will be sold next year to the owner of the car ahead of us.
  • by Animats (122034) on Friday April 11, 2008 @02:07AM (#23033238) Homepage

    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.

    • Re: (Score:2, Informative)

      by randyjparker (543614)
      I worked on the SR-71 engine (the J-58, aka JT-11D) at Pratt & Whitney. The inlet unstart problem was not related to combustion instability, but to the difficulty of sealing the inlet spike shock to the nacelle lip as atmospheric conditions changed. You run into meteorological changes quickly when you're flying faster than a .50 caliber bullet. When the inlet shock did not meet the lip, some of the pressure behind the shock would "spill" out of the compressor and cause an engine flame-out. http:// [mobiledyne.com]
    • 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

  • by Baldrson (78598) * on Friday April 11, 2008 @04:06AM (#23033714) Homepage Journal
    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.
    • by DynaSoar (714234)

      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

  • For you see, I am a professional acoustician, and now I have PROOF that playing with sound IS rocket science!
  • Living in Florida, I have seen the Shuttle launch a few times in person.

    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
  • 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!

  • I know TFA is about the imaging technique using a simulator... but now that they can analyze the problem... why not see it as a happy accident and attempt to harness the energy that is causing the problems?

    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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