Supercavitation
Overview
 
Supercavitation is the use of cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...

 effects to create a bubble of gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 inside a liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 large enough to encompass an object traveling through the liquid, greatly reducing the skin friction drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

 on the object and enabling achievement of very high speeds. Current applications are mainly limited to projectiles or very fast torpedoes
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

, but in principle the technique could be extended to include vehicles.

In water, cavitation occurs when water pressure is lowered below its vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...

, forming bubbles of vapor in the liquid.
Encyclopedia
Supercavitation is the use of cavitation
Cavitation
Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...

 effects to create a bubble of gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

 inside a liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...

 large enough to encompass an object traveling through the liquid, greatly reducing the skin friction drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

 on the object and enabling achievement of very high speeds. Current applications are mainly limited to projectiles or very fast torpedoes
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

, but in principle the technique could be extended to include vehicles.

In water, cavitation occurs when water pressure is lowered below its vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...

, forming bubbles of vapor in the liquid. That can happen when water is accelerated to high speeds as when turning a sharp corner around a piece of metal such as a ship's propeller or a water pump's impeller. The greater the water depth (or pressure for a water pipe) at which the fluid acceleration occurs, the less the tendency for cavitation because of the greater difference between local pressure and vapor pressure. Once the flow slows down again the water vapor will generally be reabsorbed into the liquid water. That can be a problem for ship propellers if cavitation bubbles implode on the surface of the propeller, applying a small force that is highly concentrated in both location and time, causing damage.

A common occurrence of water vapor bubbles is observed in a pan of boiling water. In the case of boiling, the water pressure is not reduced, but rather, the vapor pressure of the water is increased by means of heating. If the heat source is sufficient, the bubbles will detach from the bottom of the pan and rise to the surface as steam. Otherwise if the pan is removed from the heat the bubbles will be reabsorbed into the water as it cools, possibly causing pitting on the bottom of the pan as the bubbles implode.

A supercavitating object uses cavitation in a much larger and sustained manner than with the (typical) ship's propeller (hence the name supercavitation). A supercavitating object's main features are a specially shaped nose, usually flat with sharp edges, and a streamlined, hydrodynamic and aerodynamic shape. When the object is traveling through water at high speeds, the flat nose deflects the water radially outward at speeds such that there is a tremendous drop in pressure aft of where the water passes over the sharp edge of the periphery of the nose, causing a cavitation bubble that will generally close in behind the object. The bubble will persist, traveling with the object, forming at the nose and closing in behind. If the resulting cavity is not large enough, it can be extended by internally generating additional gas to inject into the cavity. The result is that the only portion of the object in direct contact with the water is the nose, and skin friction drag is substantially reduced.

The great speed required for supercavitation to work can be achieved temporarily by a projectile fired under water or by an airborne projectile impacting the water. For sustained operation rocket propulsion can be used, which by its nature adds gas at high pressure to the cavitation bubble. An example of this is the Russian Shkval supercavitating torpedo. Maneuvering can be achieved by various methods such as drag fins that project through the bubble and into the surrounding liquid (p.22), by tilting the flat surface on the nose of the object, by injecting gas asymmetrically near the nose of the object in order to distort the geometry of the cavity, or by vectoring the thrust for rocket propulsion (by gimballing or by differential thrust from multiple nozzles).

Applications

In 1960, USSR started developing project under codename "Шквал" (Squall) run by NII-24 (Kiev) to develop a high-speed torpedo, an underwater rocket, four to five times faster than traditional torpedoes capable of combating enemy submarines. Several models of device were made, the most successful – M-5 – was created by 1972. In 1972 to 1977, over 300 test launches were made (95% of them on Issyk Kul lake
Issyk Kul
Issyk Kul is an endorheic lake in the northern Tian Shan mountains in eastern Kyrgyzstan. It is the tenth largest lake in the world by volume and the second largest saline lake after the Caspian Sea. Although it is surrounded by snow-capped peaks, it never freezes; hence its name, which means "hot...

), by 29 November 1972 VA-111 Shkval
VA-111 Shkval
The VA-111 Shkval torpedo and its descendants are supercavitating torpedoes developed by the Soviet Union. They are capable of speeds in excess of 200 knots .-Design and capabilities:...

 was put into service with mass production started in 1978.

In 2004, German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 weapons manufacturer Diehl BGT Defence
Diehl BGT Defence
Diehl BGT Defence GmbH & Ko KG is a German arms manufacturer and a subsidiary of the Diehl Stiftung GmbH with headquarters in Überlingen. Diehl BGT Defence produces mainly missiles and ammunition....

 announced their own supercavitating torpedo, Barracuda, now officially named "Superkavitierender Unterwasserlaufkörper" or "supercavitating underwater running body".
(English translation) According to Diehl, it reaches more than 400 kilometres per hour (248.5 mph).

In 1994, the US Navy began developing a sea mine
Naval mine
A naval mine is a self-contained explosive device placed in water to destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, an enemy vessel...

 clearance
Demining
Demining or mine clearance is the process of removing either land mines, or naval mines, from an area, while minesweeping describes the act of detecting of mines. There are two distinct types of mine detection and removal: military and humanitarian.Minesweepers use many tools in order to accomplish...

 system invented by C Tech Defense Corporation, known as RAMICS (Rapid Airborne MIne Clearance System), based on a supercavitating projectile stable in both air and water. These have been produced in 12.7 millimetre (0.5 in), 20 millimetre (0.78740157480315 in), and 30 millimetres (1.2 in) diameters. The terminal ballistic design of the projectile allowed it to cause explosive destruction of sea mines as deep as 45 metres (147.6 ft) underwater with a single round. In 2000, these projectiles were used to successfully destroy a range of live underwater mines when fired from a hovering Sea Cobra gunship at Aberdeen Proving Ground
Aberdeen Proving Ground
Aberdeen Proving Ground is a United States Army facility located near Aberdeen, Maryland, . Part of the facility is a census-designated place , which had a population of 3,116 at the 2000 census.- History :...

s. RAMICS is currently undergoing development by Northrop Grumman
Northrop Grumman
Northrop Grumman Corporation is an American global aerospace and defense technology company formed by the 1994 purchase of Grumman by Northrop. The company was the fourth-largest defense contractor in the world as of 2010, and the largest builder of naval vessels. Northrop Grumman employs over...

 for introduction into the fleet. The darts of German (Heckler & Koch P11) and Russian underwater firearms
APS Underwater Assault Rifle
The APS Underwater Assault Rifle is an AK-47 derivative designed by the Soviet Union in the early 1970s as an underwater firearm. It was adopted in 1975. It is made by the Tula Arms Plant in Russia...

, and other similar weapons are also supercavitating.

In 2005, DARPA announced the 'Underwater Express program', a research and evaluation bid to establish the potential of supercavitation. The program's ultimate goal is a new class of underwater craft for littoral
Littoral (military)
Littoral combat is a term in military and naval warfare. It refers to operations in and around the littoral zone, within a certain distance of shore, including surveillance, mine-clearing and support for landing operations and other types of combat shifting from water to ground, and back.The...

 missions that can transport small groups of Navy personnel or specialized military cargo at speeds up to 100 knots. The contracts were awarded to Northrop Grumman and General Dynamics Electric Boat in late 2006. In 2009, DARPA announced progress via a new class of submarine.

Iran
Iran
Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

 claimed to have successfully tested its first supercavitation torpedo on 2 April and 3 April 2006. Some sources have speculated it is based on the Russian VA-111 Shkval
VA-111 Shkval
The VA-111 Shkval torpedo and its descendants are supercavitating torpedoes developed by the Soviet Union. They are capable of speeds in excess of 200 knots .-Design and capabilities:...

 supercavitation torpedo, which travels at the same speed. Russian Foreign Minister Sergei Lavrov denied supplying Iran with the technology. Iran called this weapon the Hoot
Hoot (missile)
Hoot is an Iranian supercavitation torpedo that travels at approximately 360 km/h, several times faster than a conventional torpedo. It was test-fired successfully from a surface ship against a dummy submarine during the Iranian military exercise "Great Prophet" ) on 2 April 2006 and 3 April...

 (Whale).

Alleged applications

The Kursk
Russian submarine K-141 Kursk
K-141 Kursk was an Oscar-II class nuclear-powered cruise missile submarine of the Russian Navy, lost with all hands when it sank in the Barents Sea on August 12, 2000...

submarine accident is rumored to have been due to a faulty Shkval torpedo.

See also

  • "Shkval" supercavitating torpedo
    VA-111 Shkval
    The VA-111 Shkval torpedo and its descendants are supercavitating torpedoes developed by the Soviet Union. They are capable of speeds in excess of 200 knots .-Design and capabilities:...

  • APS amphibious rifle
  • SPP-1 underwater pistol
    SPP-1 Underwater Pistol
    The SPP-1 Underwater Pistol was made in the USSR for use underwater by Soviet frogmen as an underwater firearm. It was developed in the late 1960s and accepted for use in 1971. Underwater, ordinary-shaped bullets are inaccurate and very short-range...

  • Supercavitating propeller
    Supercavitating propeller
    The supercavitating propeller is a variant of a propeller for propulsion in water, where supercavitation is actively employed to gain increased speed by reducing friction...


External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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