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What is Supercavitation?

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  • Written By: Michael Anissimov
  • Edited By: Bronwyn Harris
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  • Last Modified Date: 11 November 2016
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Supercavitation is a remarkable technology which most people have never heard of. By reducing drag on submarines and torpedoes by a factor of 60-70%, supercavitation could transform the stealthy world of submarine warfare into something more like aerial combat, with objects flying back and forth at speeds much faster than the submarines we know.

Supercavitation exploits the phenomena of cavitation, something that submarine designers usually try to avoid. It would work as follows. When the nose of a torpedo or submarine is shaped in a certain way, usually flat with sharp edges, it creates an excessive amount of drag through the water. But the design of the nose accelerates the water it moves through at quick speeds, causing it to lose pressure and vaporize into bubbles. This follows from the well-known Bernoulli's principle, which states that fluid velocity and pressure/density are related. When the velocity increases, the density drops. When the density drops below the vapor pressure of the water, the water vaporizes until it slows down enough to recondense.

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By purposefully vaporizing as much water as it can, a supercavitating submarine or torpedo can create a bubble of air so large that it encompasses the whole vehicle. This is a positive feedback process - the more water is vaporized by the specially designed nose, the less drag on the vehicle, the easier it gets to move even faster and vaporize more water. The primary downside is that a supercavitating object is extremely loud. It churns water with such abandon that a shock wave would emanate out from the vehicle wherever it went. This, along with technological challenges, is the reason why supercavitating submarines have not yet been developed, although they are in the works. Supercavitating torpedoes have experienced limited use.

As with many interesting technological advancements, torpedoes exploiting supercavitation were originally developed by the Germans during WWII. Subsequently they were abandoned and taken up by the Russians. In recent years, the United States has taken a great interest in the technology, working on an "Underwater Express" program to create a supercavitating underwater battleship. Developing powerful underwater military capability is essential for national security because of the threat of nuclear submarines.

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anon142671
Post 5

Purposeful vaporization is not necessary as some of the rocket engine's exhaust can be forced out of the nose to create and maintain the bubble and then redirect to the tail once a natural bubble is formed.

Even if almost half the exhaust is spent out of the nose, the decrease in resistance should be enough to accelerate the torpedo forward rather quickly, even with a 49 percent nose to 51 percent tail exhaust distribution.

The whole idea is that high acceleration rates take insignificant amounts of thrust as friction starts to approach zero (see space shuttle's massive boosters needed to leave earth and minuscule boosters needed to maneuver in space).

Cavitation causes "earthquakes" as air bubbles are liquefied. In

contrast, supercavitation maintains the bubble intact, well at least until the torpedo strikes and the bubble collapses, and even then, the energy released by the cavitation is insignificant when compared with the kinetic energy released on impact. A 2.5 tonne torpedo going from 300km/h to zero and the subsequent chemical or nuclear explosion as the warhead goes off before the torpedo can exit the target (assuming it has a penetrator).

Anti ship torpedoes normally do not have penetrators and simply go off under the target to raise it out of the water and cause the keel to rupture. Supercavitating submarines are impractical as their bubbles collapsing every time they stop will cause structural damage. That problem does not arise with a torpedo as it only needs to stop once.

time
Post 4

Can we say by the way propeller acts in the air instead of water that is why the speed of submarine increases?

anon39996
Post 2

I've read that super cavitating torpedoes carry gas onboard to generate bubble envelope. How can you reach speeds fast enough to "purposefully" vaporize water? I would assume that even the rocket motor would be hampered at launch if no bubble "jacket" was present.

anon11368
Post 1

Interesting, gee I wonder if an earthquake could be spawned via super-cavitation. Of course no one would ever use that technology.

Humans are too ethical to do that.

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