What is supercavitation? (with photos)

Submarine propellers can cause cavitation.

Supercavitation is a remarkable technology that most people have never heard of. By reducing the drag of submarines and torpedoes by a factor of 60-70%, supercavitation could transform the stealthy world of submarine warfare into something more akin to air combat, with objects flying back and forth at speeds much faster than than the submarines we know.

Supercavitation exploits the phenomenon of cavitation, something submarine designers often try to avoid. It would work as follows. When the nose of a torpedo or submarine is a specific shape, usually flat with sharp edges, it creates an excessive amount of drag through the water. But the nose design accelerates the water it moves through at high speed, causing it to lose pressure and vaporize into bubbles. This stems from the well-known Bernoulli principle, which states that fluid velocity and pressure/density are related. As speed increases, density decreases. When the density drops below the vapor pressure of water, the water vaporizes until it decreases enough to recondense.

The US Navy uses several nuclear-powered submarines, such as the Ohio-class submarine.

By intentionally vaporizing as much water as possible, a supercavitating submarine or torpedo can create an air bubble so large that it envelops the entire vehicle. This is a positive feedback process – the more water that is vaporized through the specially designed nose, the less resistance the vehicle has, the easier it becomes even faster and vaporizes more water. The main disadvantage is that a supercavitating object is extremely noisy. It churns the water with such abandon that a shock wave would emanate from the vehicle wherever it went. This, along with the technological challenges, is the reason why supercavitating submarines have not yet been developed, although they are in the works. Supercavitating torpedoes have limited use.

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As with many interesting technological advances, torpedoes that exploit supercavitation were originally developed by the Germans during World War II. Subsequently, they were abandoned and taken by the Russians. In recent years, the United States has shown great interest in the technology, working on an “Underwater Express” program to create a supercavitating underwater warship. The development of a powerful underwater military capability is essential for national security due to the threat of nuclear submarines.

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