Supercavitating
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Supercavitation is the use of a cavitation bubble to reduce skin friction
drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adj ...
on a submerged object and enable high speeds. Applications include
torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, s ...
es and
propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
s, but in theory, the technique could be extended to an entire underwater vessel.


Physical principle

Cavitation is the formation of vapour bubbles in liquid caused by flow around an object. Bubbles form when water accelerates around sharp corners and the pressure drops below the vapour pressure. Pressure increases upon deceleration, and the water generally reabsorbs the vapour; however, vapour bubbles can implode and apply small concentrated impulses that may damage surfaces like ship propellers and pump impellers. The potential for vapour bubbles to form in a liquid is given by the nondimensional cavitation number. It equals local pressure minus vapour pressure, divided by dynamic pressure. At increasing depths (or pressures in piping), the potential for cavitation is lower because the difference between local pressure and vapour pressure is greater. A supercavitating object is a high-speed submerged object that is designed to initiate a cavitation bubble at its nose. The bubble extends (either naturally or augmented with internally generated gas) past the
aft "Aft", in nautical terminology, is an adjective or adverb meaning towards the stern (rear) of the ship, aircraft or spacecraft, when the frame of reference is within the ship, headed at the fore. For example, "Able Seaman Smith; lie aft!" or "Wh ...
end of the object and prevents contact between the sides of the object and the liquid. This separation substantially reduces the skin friction drag on the supercavitating object. A key feature of the supercavitating object is the nose, which typically has a sharp edge around its perimeter to form the cavitation bubble. The nose may be articulated and shaped as a flat disk or cone. The shape of the supercavitating object is generally slender so the cavitation bubble encompasses the object. If the bubble is not long enough to encompass the object, especially at slower speeds, the bubble can be enlarged and extended by injecting high-pressure gas near the object's nose. The very high speed required for supercavitation can be temporarily reached by underwater-fired projectiles and projectiles entering water. For sustained supercavitation, rocket propulsion is used, and the high-pressure rocket gas can be routed to the nose to enhance the cavitation bubble. In principle, supercavitating objects can be maneuvered using various methods, including the following: * Drag fins that project through the bubble into the surrounding liquid (p. 22) * A tilted object nose * Gas injected asymmetrically near the nose to distort the cavity's geometry * Vectoring rocket thrust through gimbaling for a single nozzle * Differential thrust from multiple nozzles


Applications

The Russian Navy developed the
VA-111 Shkval The VA-111 ''Shkval'' (from russian: шквал, ''squall'') torpedo and its descendants are supercavitating torpedoes originally developed by the Soviet Union. They are capable of speeds in excess of 200 knots (370 km/h or 230 miles/h). D ...
supercavitation
torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, s ...
, which uses rocket propulsion and exceeds the speed of conventional torpedoes by at least a factor of five. NII-24 began development in 1960 under the code name "Шквал" (Squall). The VA-111 Shkval has been in service (exclusively in the Russian Navy) since 1977 with mass production starting in 1978. Several models were developed, with the most successful, the M-5, completed by 1972. From 1972 to 1977, over 300 test launches were conducted (95% of them on Issyk Kul lake). In 2006, German weapons manufacturer Diehl BGT Defence announced their "own" supercavitating torpedo, the Barracuda, now officially named ' ( en, supercavitating underwater projectile). According to Diehl, it reaches speeds greater than . In 1994, the United States Navy began development of the Rapid Airborne Mine Clearance System (RAMICS), a sea mine clearance system invented by C Tech Defense Corporation. The system is based on a supercavitating projectile stable in both air and water. RAMICS projectiles have been produced in diameters of , , and . The projectile's terminal ballistic design enables the explosive destruction of sea mines as deep as with a single round. In 2000 at Aberdeen Proving Ground, RAMICS projectiles fired from a hovering Sea Cobra gunship successfully destroyed a range of live underwater mines. As of March 2009, Northrop Grumman completed the initial phase of RAMICS testing for introduction into the fleet.
Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkm ...
claimed to have successfully tested its first supercavitation torpedo, the
Hoot Hoot may refer to: Publications * ''Hoot'' (novel), a young adult novel by Carl Hiaasen * ''Hoot'', a 1996 children's novel by Jane Hissey * ''Hoot'' (comics), a British magazine published from 1985 to 1986 * '' The Brandeis Hoot'', a student n ...
(Whale), on 2–3 April 2006. Some sources have speculated it is based on the Russian
VA-111 Shkval The VA-111 ''Shkval'' (from russian: шквал, ''squall'') torpedo and its descendants are supercavitating torpedoes originally developed by the Soviet Union. They are capable of speeds in excess of 200 knots (370 km/h or 230 miles/h). D ...
supercavitation torpedo, which travels at the same speed. Russian Foreign Minister
Sergey Lavrov Sergey Viktorovich Lavrov (russian: Сергей Викторович Лавров, ; born 21 March 1950) is a Russian diplomat and politician who has served as the Minister of Foreign Affairs (Russia), Foreign Minister of Russia since 2004. ...
denied supplying Iran with the technology. In 2004,
DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Ad ...
announced the Underwater Express program, a research and evaluation program to demonstrate the use of supercavitation for a high-speed underwater craft application. The US Navy's ultimate goal is a new class of underwater craft for littoral missions that can transport small groups of navy personnel or specialized military cargo at speeds up to 100 knots. DARPA awarded contracts to Northrop Grumman and General Dynamics Electric Boat in late 2006. In 2009, DARPA announced progress on a new class of submarine: A prototype ship named the ''
Ghost A ghost is the soul or spirit of a dead person or animal that is believed to be able to appear to the living. In ghostlore, descriptions of ghosts vary widely from an invisible presence to translucent or barely visible wispy shapes, to rea ...
'', uses supercavitation to propel itself atop two struts with sharpened edges. It was designed for stealth operations by Gregory Sancoff of
Juliet Marine Systems Juliet Capulet () is the female protagonist in William Shakespeare's romantic tragedy ''Romeo and Juliet''. A 13-year-old girl, Juliet is the only daughter of the patriarch of the House of Capulet. She falls in love with the male protagonist ...
. The vessel rides smoothly in choppy water and has reached speeds of 29 knots. The Chinese Navy and
US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
are reportedly working on their own supercavitating
submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s using technical information obtained on the Russian VA-111 Shkval supercavitation torpedo. A
supercavitating propeller {{no footnotes, date=November 2016 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. They are being used for military purpo ...
uses supercavitation to reduce water skin friction and increase propeller speed. The design is used in military applications, high-performance racing
boat A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size, shape, cargo or passenger capacity, or its ability to carry boats. Small boats are typically found on i ...
s, and model racing boats. It operates fully submerged with wedge-shaped blades to force cavitation on the entire forward face, starting at the leading edge. Since the cavity collapses well behind the blade, the supercavitating propeller avoids spalling damage caused by cavitation, which is a problem with conventional propellers. Supercavitating ammunition is used with German ( Heckler & Koch P11) and Russian
underwater firearms An underwater firearm is a firearm designed for use underwater. They are in the arms inventories of many nations. A common feature of underwater firearms or needleguns is that they fire flechettes or spear-like bolts instead of standard bullet ...
, and other similar weapons.


Alleged incidents

The ''Kursk'' submarine disaster was initially thought to have been caused by a faulty Shkval supercavitating torpedo, though later evidence points to a faulty 65-76 torpedo.


See also

* Supercavitating torpedo * "Shkval" supercavitating torpedo * APS amphibious rifle * SPP-1 underwater pistol *
Supercavitating propeller {{no footnotes, date=November 2016 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. They are being used for military purpo ...


References

{{Reflist


Further reading

*Office of Naval Research (2004, June 14). Mechanics and energy conversion: high-speed (supercavitating) undersea weaponry (D&I). Retrieved April 12, 2006, fro
Office of Naval Research Home Page
*Savchenko Y. N. (n.d.). CAV 2001 - Fourth Annual Symposium on Cavitation - California Institute of Technology Retrieved April 9, 2006, archived a
Wayback Machine
*Hargrove, J. (2003). Supercavitation and aerospace technology in the development of high-speed underwater vehicles. In ''42nd AIAA Aerospace Sciences Meeting and Exhibit''. Texas A&M University. *Kirschner et al. (2001, October) Supercavitation research and development. ''Undersea Defense Technologies'' *Miller, D. (1995). Supercavitation: going to war in a bubble. ''Jane's Intelligence Review''. Retrieved Apr 14, 2006, fro
Defence & Security Intelligence & Analysis , Jane's 360
*Graham-Rowe, & Duncan. (2000). Faster than a speeding bullet. ''NewScientist'', 167(2248), 26–30. * Tulin, M. P. (1963). Supercavitating flows - small perturbation theory. Laurel, Md, Hydronautics Inc. *Niam J W (Dec 2014), Numerical Simulation Of Supercavitation


External links


Supercavitation Research Group at the University of MinnesotaDiehl BGT Defence's "Barracuda" - a German supercavitating TorpedoDARPA Underwater Express ProgramHow to Build a Supercavitating Weapon, Scientific American
Fluid dynamics