Supercavitation
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Supercavitation is the use of a cavitation bubble to reduce skin friction drag 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, su ...
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 Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...
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 Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases ...
. 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 The Euler number (Eu) is a dimensionless number used in fluid flow calculations. It expresses the relationship between a local pressure drop caused by a restriction and the kinetic energy per volume of the flow, and is used to characterize ener ...
. It equals local pressure minus vapour pressure, divided by
dynamic pressure In fluid dynamics, dynamic pressure (denoted by or and sometimes called velocity pressure) is the quantity defined by:Clancy, L.J., ''Aerodynamics'', Section 3.5 :q = \frac\rho\, u^2 where (in SI units): * is the dynamic pressure in pascals ( ...
. 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 end of the object and prevents contact between the sides of the object and the liquid. This separation substantially reduces the
skin friction drag Skin friction drag is a type of aerodynamic or hydrodynamic drag, which is resistant force exerted on an object moving in a fluid. Skin friction drag is caused by the viscosity of fluids and is developed from laminar drag to turbulent drag as a f ...
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). ...
supercavitation Supercavitation is the use of a cavitation bubble to reduce skin friction drag on a submerged object and enable high speeds. Applications include torpedoes and propellers, but in theory, the technique could be extended to an entire underwater v ...
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, su ...
, 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 Issyk-Kul (also Ysyk-Köl, ky, Ысык-Көл, lit=warm lake, translit=Ysyk-Köl, , zh, 伊塞克湖) is an endorheic lake (i.e., without outflow) in the Northern Tian Shan mountains in Eastern Kyrgyzstan. It is the seventh-deepest lake in th ...
). In 2006,
German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
weapons manufacturer
Diehl BGT Defence Diehl Defence GmbH & Co. KG is a German arms manufacturer and a division of the Diehl Stiftung with headquarters in Überlingen. Diehl Defence mainly produces missiles and ammunition. Diehl BGT Defence was founded in 2004 as result of the merge ...
announced their "own"
supercavitating torpedo A supercavitating torpedo is a torpedo using the effect of supercavitation to create a bubble around the torpedo to move at high velocity under water. The following is a list of supercavitating torpedoes which have been developed or are in developm ...
, the Barracuda, now officially named ' ( en, supercavitating underwater projectile). According to Diehl, it reaches speeds greater than . In 1994, the
United States 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 ...
began development of the Rapid Airborne Mine Clearance System (RAMICS), a
sea mine A naval mine is a self-contained explosive device placed in water to damage or 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, any v ...
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 Aberdeen Proving Ground (APG) (sometimes erroneously called Aberdeen Proving ''Grounds'') is a U.S. Army facility located adjacent to Aberdeen, Harford County, Maryland, United States. More than 7,500 civilians and 5,000 military personnel work at ...
, RAMICS projectiles fired from a hovering Sea Cobra gunship successfully destroyed a range of live underwater mines. As of March 2009,
Northrop Grumman Northrop Grumman Corporation is an American multinational aerospace and defense technology company. With 90,000 employees and an annual revenue in excess of $30 billion, it is one of the world's largest weapons manufacturers and military techn ...
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 Turkmeni ...
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). ...
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 Adv ...
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 The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal areas ...
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 General Dynamics Electric Boat (GDEB) is a subsidiary of General Dynamics Corporation. It has been the primary builder of submarines for the United States Navy for more than 100 years. The company's main facilities are a shipyard in Groton, Co ...
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 Gregory may refer to: People and fictional characters * Gregory (given name), including a list of people and fictional characters with the given name * Gregory (surname), a surname Places Australia * Gregory, Queensland, a town in the Shire o ...
of Juliet Marine Systems. The vessel rides smoothly in choppy water and has reached speeds of 29 knots. The
Chinese Navy The People's Liberation Army Navy (PLAN; ), also known as the People's Navy, Chinese Navy, or PLA Navy, is the maritime service branch of the People's Liberation Army. The PLAN traces its lineage to naval units fighting during the Chine ...
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 of ...
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 Skin friction drag is a type of aerodynamic or hydrodynamic drag, which is resistant force exerted on an object moving in a fluid. Skin friction drag is caused by the viscosity of fluids and is developed from laminar drag to turbulent drag as a f ...
and increase propeller speed. The design is used in military applications, high-performance
racing In sport, racing is a competition of speed, in which competitors try to complete a given task in the shortest amount of time. Typically this involves traversing some distance, but it can be any other task involving speed to reach a specific goa ...
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 inl ...
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
spall Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ba ...
ing damage caused by cavitation, which is a problem with conventional propellers. Supercavitating ammunition is used with German (
Heckler & Koch P11 The HK P11 is a Heckler & Koch pistol designed as an underwater firearm that was developed in 1976. It has five barrels and each fires a 7.62 X 36mm dart electrically. Loading is by means of a five-round case. The design resembles that of a peppe ...
) and Russian underwater firearms, 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 A supercavitating torpedo is a torpedo using the effect of supercavitation to create a bubble around the torpedo to move at high velocity under water. The following is a list of supercavitating torpedoes which have been developed or are in developm ...
* "Shkval" supercavitating torpedo *
APS amphibious rifle The APS underwater assault rifle (APS stands for ''Avtomat Podvodny Spetsialnyy'' (Автомат Подводный Специальный) or "Special Underwater Assault Rifle") is an underwater firearm designed by the Soviet Union in the ear ...
* 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