Mysterious Sound Waves Can Destroy Rockets

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.'"

Defense System?

[BountyX]

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

Re:Defense System?

[evanbd]

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.

Re:Defense System?

[Hojima]

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 systems will be at a prime. Though the best missile defense is undoubtedly diplomacy.

Re:Didn't Nikola Tesla talk about something like t

[Anonymous Coward]

well hey, thanks for posting. something you might have heard about somewhere about a subject you very likely have no knowledge about whatsoever. i can guess that by the complete lack of anything useful in your post. let me go way out on a limb here and guess that your age is 14 years or less. 15 tops. in the future, be useful or silent. thanks!

Re:Look, I can see science media dumbing it down

[Forbman]

pressure waves...acoustic waves... Hmm... I'm having a hard time seeing the difference. I think they use "acoustic" because of their frequency is probably between 20Hz-20KHz... otherwise known as "acoustic".

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 these rotating acoustic waves are just a form of conservation of (angular) momentum in the fluid flow that under less pressured circumstances would want to make a vortex?

Re:Somthing Wrong Here. was Re:Nothing new here

[TapeCutter]

IIRC engineers are still disputing the cause so I don't think the de-bunking is coming to a conclusion anytime soon. Yes, the mythbusters failed induce resonance when they tried, but they also failed to mention the Wobbly Bridge.

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 you watch the video [youtube.com] it's quite easy to see that the cables are indeed carrying waves.

I accept that the deck of a suspension bridge is designed to move in the wind like tall buildings do, and also that bad areodynamics could easily induce a twisting of the deck in the right conditions. However it's a long bow to draw to say that the deck flapped itself to destruction in a 40mph wind while at the same time totally dismissing the compounding effects of resonance.

Re:No, those are not sound waves

[SQLGuru]

If the waves reach the ear drum and are interpreted, would they become sound? Sound is vibration through a medium that is perceived by something. If I make waves in a jump rope at the right frequency, I'm pretty sure I can hear it. Just because the device (human ear) isn't sensitive enough to detect it doesn't mean it isn't sound.

Layne

Re:Good news!

[susano_otter]

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.