Supercavitation

Supercavitation . It is a hydrodynamic phenomenon related to the cavitation of objects that travel at high speed within a fluid. Contrary to cavitation, which is generally a phenomenon with negative effects on naval or aeronautical engineering , supercavitation is used as a way to solve resistance problems that objects offer to move within a fluid.

Summary

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  • 1 Principles
  • 2 Applications
  • 3 See also
  • 4 References
  • 5 Sources

Beginning

The cavitation is usually an undesirable effect on any type of fluid machinery. It occurs when somewhere in a liquid at high speed a depression is formed so strong that the liquid changes to its gas form. The problem itself is not the gas, but the bubbles that form, when collapsing in the form of small explosions, destroy everything that is nearby, and that is why it is so critical to avoid them in, for example, hydraulic pumps or propellers. ships (in addition to a huge loss in their efficiency).

When a body moves rapidly within a fluid, the pressure at various points on the body is reduced. The faster the body moves, the lower the pressure. But when the pressure is lowered enough to equal the vapor pressure of the fluid, the liquid state cannot be maintained. Without having enough pressure to hold together, the liquid’s molecules vaporize and form “cavities,” or bubbles. Their effect is not innocent: they can destroy a ship’s propellers, and that’s why naval architects have to do so many calculations at this point.

In pumps, turbines, and propellers, cavitation leads to two main problems. Bubbles distort flow patterns, thereby reducing efficiency. On the other hand, eventually the bubbles reach high pressure regions and collapse, creating highly violent microscopic shock waves, enough to excavate strips in the exposed metal.

Under certain conditions, a single bubble or supercavity can form, almost completely enveloping moving objects. Newton went on to draw the basic principles in his Principia Mathematica , 1687 . A body with supercavitation has extremely low resistance, because friction on its surface is almost non-existent. Instead of being surrounded by water, you surround yourself with the water vapor that forms in the bubble. Because steam has a much lower density and viscosity than liquid water, the body can move much faster.

Applications

The Shkval supercavitation torpedo at the an exhibition in Russia .

Russia is the most advanced country in studies on this topic. She developed a supercavitation torpedo that can travel at speeds of over 200 knots. This project was started by the Soviet Union at the time of the Cold War . There are rumors that the accident to the Russian submarine K-141 kursk was due to the explosion of a faulty Shkval torpedo [1] , although official sources have said that it was a conventional type 65-76 torpedo.

Iran has tested a domestically manufactured torpedo that has similar characteristics to the Shkval Russian, so probably try a copy of the same [2] .

The US Navy uses mine destruction bullets that have a flattened tip that causes a supercavity (the gas produced completely envelops the projectile), making it possible to reach 15 meters deep with enough energy to explode a mine. These bullets are fired from a helicopter gunship at the target.

In 2005 the Defense Advanced Projects Research Agency (known by its acronym in English DARPA), an agency of the United States Department of Defense , announced a submarine program that, taking advantage of this effect, could theoretically reach 100 knots, a great submarine speed advance, compared to the current 25/30 knots

 

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