This phenomenon called supercavitation uses cavitation effects to create a bubble of gas inside a liquid large enough to encompass an object travelling through the liquid, greatly reducing the skin friction drag on the object and enabling achievement of very high speeds. Supercavitating vehicle travelling faster than a passenger jet shall be capable of sailing from London to New York in just five hours.
Supercavitation happens when water is accelerated to high speeds of over 180 km/h, when the small gas bubbles produced by cavitation expand and combine to form one large, stable and predictable bubble around the supercavitating object. Supercavitation is being applied to develop a range of weapons like underwater mine bullets, homing torpedoes, submarines and boats.
Many countries are involved in research in this area Russia, followed by Ukraine in Kiev Research Institute of Hydrodynamics, France within the framework of Action Concert?e Cavitation , Germany with its Superkavitierender Unterwasserlaufkörper (“supercavitating underwater running body”) and the USA.
One of the most innovative underwater weapons developed by the Soviet Union was the VA-111 Shkval (“Squall”) supercavitating torpedo. According to the authors of the journal, “Squall”, which is the first modern weapons using supercavitation is probably the largest breakthrough in submarine warfare since the invention of the submarine itself.
China and Iran were engaged in copying Russian technology, it is reported that China bought 40 torpedoes “Squall” in Kazakhstan. Iran claims to have a supercavitating torpedo of its own it calls Hoot, and which is assumed to be a reverse-engineered Shkval. On 7 May 2017, Iranian forces reportedly test fired a Hoot In 2015, China claimed to have solved critical challenges has brought supersonic submarines close to reality.
The Pentagon in conjunction with DARPA and the US Navy, have been designing and developing a Supercavitating underwater submarine. In 2006, DARPA first announced about the ‘Underwater Express program’ whose 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 for an hour at its most basic. The contracts under which were awarded to Northrop Grumman and General Dynamics Electric Boat. While supercaivitating entire submarines have proved to be daunting tasks , US has gone ahead with developing supercvitating bullets as well as Ghost vessel which use partial supercavitation.
However, Supercavitation has many challenges, it is hard to achieve at low speed, so it is extremely hard for a submarine to even reach the speeds necessary to create the required bubble.Drag is the counter force that acts against any object moving through the water, and the greater the velocity, the greater the drag, which means that the constraints of fluid dynamics impose an effective speed limit of around 50 knots.
Now, while as the Starship Enterprise’s fictional chief engineer Montgomery Scott was wont to say, “you cannot change the laws of physics”, you can sometimes get around them, and in this case, that involves wrapping your torpedo in a giant bubble of gas.
Second Steering is also proved to be extremely difficult using conventional mechanisms, such as a rudder, which are inside the bubble without any direct contact with water.
The supercavitation technique was first devised by the Soviets in 1960, and Dagdieselfactory utilized it to develop supercavitating underwater torpedo called the Shkaval, that could travel through the water at speeds of up to 200 knots (~230 mph, 370 kph).
It used a rocket engine for propulsion instead of propellers or pumpjets used by traditional torpedoes. The hot rocket exhaust gas was ejected through a conical disk at its nose to create the gas cavity that completely enveloped the projectile. Traveling through gas the torpedo encounters much less drag, allowing it to move at speeds of up 200 knots.
The torpedo is of standard 533-millimeter torpedo diameter and carries a 460 pound warhead. It has a maximum range of 7,500 yards. Shkval began mass production in 1978 and entered service with the Soviet Navy that year.
Its drawbacks, however, are its loudness and its short launch distance – all of 5-6 miles. This is guaranteed to unmask the submarine-carrier, so that its own survival would have been put in question. Its primitive guidance system also made turning maneuvers tricky, as a change of heading forced a portion of the torpedo outside the bubble, causing sudden drag at 230 miles an hour. The large noise also disabled the torpedo’s built-in active and passive sonar guidance systems.
Russia is now modernizing VA-111 ‘Shkval’, making changes to its design, shape, and even application tactics, as reported by AlexánderKorolkov. ShamilAliev, Chief designer at Dagdiesel factory in southern Russia’s sunny Daghestan, stated that he personally participated in designing the hydrodynamic shape of its upgraded version. This work involved determining the boundaries of the water and air around the torpedo, which would make it possible to determine its weight and size limits.
He also said,”Replacing the ‘Shkval’s’ inertial navigation system with a modern, dynamic one will increase the range for destroying targets, and will make it possible to create a fundamentally new weapon on that basis.” “The torpedo should not just hit the body of the enemy, but strike at the most vulnerable spot, the commander’s compartment or a control compartment. Do not forget that a submarine can only be destroyed by a torpedo. It is impossible to destroy one with a missile,” explained Aliev.
The improved motors and better fuels could give the next generation of supercavitating torpedoes perhaps ten times that range, and possibly ten times the speed, according to naval technology.com
DARPA’s Underwater Express
DARPA’s requirements, outlined in a broad agency announcement, included using supercavitation to demonstrate stable and controllable high-speed underwater transport. The agency and developers hoped to enable a new class of underwater craft for future littoral missions transporting high-value cargo and small units of personnel. According to DARPA, the large cavity and maneuvering control system required for this type of vehicle never has been created.
Phase 1 of the Underwater Express program was focused on stable cavity generation and sustainment by examining supercavitation physics and the interaction between the cavity and the body. Developers will generate a system concept for an 8-foot-diameter, 60-metric-ton notional superfast submerged transport (SST) craft. The contractors also must create an initial concept design of the control system for all vehicle operating conditions.
By sustaining high velocity, the vessel will be able to outlast torpedo threats. Standard torpedoes run below the supercavitation range at approximately 40 to 60 knots and can be controlled, while nuclear-powered submarines travel at speeds greater than 25 knots. The Underwater Express Program will provide the advantages of higher speed along with the ability to control the vehicle.
Rear Adm. John B. Padgett III, USN (Ret.), vice president for business development and strategic planning, General Dynamics, said, “In the demonstrations to date where you had anybody in water going that fast, there is a tendency for it to be unstable, and the instability increases with the speed.” Adm. Padgett stressed that the importance of this project is not only the speed but also the ability to maintain the rapid pace and to control the vehicle at that rate.
The Underwater Express program has several possible applications, and DARPA says it potentially could be manned. Examples of manned uses include special operations such as the U.S. Navy SEALs would carry out. By using the supercavitation technology, the Navy would reduce the amount of time required for SEALs to reach their objective point. In combat situations, the technology would give U.S. forces more agility to avoid attack by a large spectrum of adversaries that move at slower speeds or are less controlled.
The project also has applications for logistics issues in the military and in the commercial world. “Instead of transiting the ocean at 50 knots, you could do it at 200 knots,” Adm. Padgett states. Besides delivering materiel to troops more quickly, this technology would allow shipping companies to invest in marine fleets instead of aircraft for their transport requirements. The military and corporations could load more cargo and deliver it to points of interest faster than current methods permit.
Integrating the technology onto a submarine platform is one of the program’s major problems. Making a piece of metal or plastic move quickly in water may be interesting but is fundamentally irrelevant, according to Adm. Padgett. Once the technology is demonstrated, developers have to meld it with the platform efficiently and effectively and demonstrate success again.
Adm. Padgett compares the process of the supercavitation technology to the advance of aircraft. From air travel that began with propellers, scientists have created jets that fly at speeds of Mach 3, and the space shuttle can attain speeds faster than that. In the same way, the Underwater Express program will move undersea vessels into the next realm of speed and capability, though rapidly moving objects through water is more difficult than moving them through air.
In the next phases of the project, developers will focus on supercavitation effects and eventually will work toward the final demonstration. Phase 2 includes continued examination of supercavitation physics, cavity-vehicle interactions and the development of vehicle control. At this stage, propulsion concepts will be integrated and maneuvering and body forces as well as gas expenditures will be characterized and measured.
Two years later, the US Defence Advanced Research Projects Agency (DARPA) commissioned General Dynamics to look into the technology. It seems that they were exploring the possibility of overcoming the sonar limitations by changing the design of the cavitation disc, altering the location of the transmitters and developing special noise-cancelling filters to cut out interference from the engine, according to naval technology .com.
While supercaivitating entire submarines have proved to be daunting tasks , US has gone ahead with developing supercvitating bullets as well as Ghost vessel which use partial supercavitation.
Supercavitating Ghost vessel has 900 times less friction than conventional watercraft
The Ghost consists of 38ft-long (11.5m) long main cabin resting on top of a pair of 12-foot (3.6m) tall struts which, when moving at speed, prop the cabin above the water like a hydrofoil. Ghost has demonstrated reaching speeds of 33 knots (38 mph/61km/h) even when faced with waves of 8ft (2.4 metre) high by taking advantage of ‘supercavitation,’ by traveling underwater inside a bubble of gas and its design. However its creator believes it could approach 60mph (97 km/h), while staying stable even in rough seas.
‘A squadron of ten stealth Ghosts, carrying torpedos, missiles or cannons, would wreak havoc on any enemy,’ it says. Business Insider named the vessel one of the top 19 most game-changing weapons of the 21st century at the end of last year.
The struts swivel at their base, allowing them to be raised and lowered depending on depth. While parked, or traveling through shallow waters, they can be extended to the side. In deeper waters, at speeds of eight knots or higher, they rotate downward to lift the hull into the air, eliminating the jarring impact of waves.
At the other end of each strut, a 62-foot long tube houses a 2,000HP gas turbine engine spinning two front-mounted propellers. ‘It’s a revolutionary program,’ said Greg Sancoff, founder and CEO of Juliet Marine Systems. ‘Nothing like this has ever been built by anybody, not even the Navy. ‘Ghost has three new technologies that it is demonstrating,’ Mr Byrd told MailOnline.’Ride quality with ride stability using an integrated fly-by-wire closed loop control system, advanced drag reduction using
DSG Technology begins producing supercavitating bullets
DSG Technology has begun production in California of its supercavitating multi-environment ammunition (MEA), which the company said allows for shooting into and under water and better addresses multi-layered targets.
When an object encounters a liquid at speeds greater than 100 m/s, the fluid pressure behind the object is lowered below the vapour pressure of the liquid and thus forms a bubble of vapour – a cavity – that encompasses the object, according to a DSG Technology factsheet. Cav-X ammunitions has a cavitating core that in water can form a cavity that exceeds the size of the projectile, so water resistance in the cavity acts solely on the leading edge. Among other things, this allows rounds to enter and exit water more reliably, so a low-angle shot will not ricochet off the water’s surface and endanger friendly or civilian vessels, Garberg said
This means that larger calibre Cav-X ammunition could be used in defence against torpedoes from surface or submerged platforms. For example, vessels armed with a Phalanx air defence weapon could address an incoming torpedo in the same way it would address incoming missiles, without worrying that the rounds would ricochet off the water’s surface.
Garberg said the company can produce rounds in three loads: maximum, medium, and subsonic, depending on the customer’s intended application, which allows users to buy ammunition specifically for a maritime or littoral environment, or specifically to address multi-layered or armoured targets.
While the Cav-X can be applied to any calibre, DSG Technology said 5.56 mm supercavitating ammunition has a typical effective range of 700-900 m in air and 10-11 m in water, or the sub-sonic load 600 m in air and 12-14 m in water. The 7.62 mm ammunition would have a typical effective range of 1,100 m in air and 20-22 m in water, the sub-sonic load 500 m in air and 12-14 m in water. The 12.7 mm has typical effective range of 2,200 m in air and 60 m water (a sub-sonic configuration is not suitable at this calibre), according to the company.
German scientists have come to grips with the study of phenomena supercavitation late 1970s. In the late 80s the company Company Diehl BTG Defence has successfully tested underwater missile Barracuda. Barracuda is equipped with solid rocket motors, inertial navigation system, block homing turning nose cone-shaped Rocket engine provides Barracuda underwater speed of 800 km/h according to the developers. The distinctive features are inertial systems using fiber-optic gyros and automatic homing systems, antenna array which is placed in a conical fairing, also serves as the steering gear missiles.
During these tests, they have successfully demonstrated the “stable straight and curved path of movement.” Be equipped with missile-torpedo Barracuda both submarines and surface ships.
U rocket Barracuda was first presented on 17-20 May 2005, at the exhibition IMDEX in Singapore. Developer shvastatayut stated that Barracuda in its capabilities are unparalleled in the world, and that they are at least 10 years ahead of their American counterparts. In this exhibition, they did not forget to mention again that the new German submarine missile Barracuda faster and more maneuverable exact “Squall” and, thanks to a unique homing system, it is able to intercept “Squall” and other high-speed torpedo.
According to unconfirmed reports, GVW Barracuda is 110 kg, length 2300 mm, caliber 160 mm, weight 10 kg of explosives, cruising range of 1000 m, with a maximum travel speed of full circulation time of 3.6 seconds, the diameter of the circulation 120 m .
China claimed to have solved critical challenges has brought supersonic submarines close to reality
China reportedly brought 40 conventionally armed Shkval -Es from Russia in 1998 and also carrying out Supercavitation research at least for a decade on many important research topics including the study on cavitation flows, kinematics and dynamics model of strong maneuvering supercavitating vehicles, influence of cavitator diameter, cone angle, slenderness ratio of body on the anti-drag of supercavity, and longitudinal motion control of underwater high-speed vehicle.
The team of scientists at Harbin Institute of Technology’s Complex Flow and Heat Transfer Lab have claimed to have solved dual problems of supercavitation of full submarine: formulating a right conditions for supercavitation, and a second is steering a vessel.
“Our method is different from any other approach, such as vector propulsion,” or thrust created by an engine, Harbin highbrow Li Fengchen said. “By combining liquid-membrane technology with supercavitation, we can significantly reduce the launch challenges and make cruising control easier.” In theory, supercavitation could allow for speeds up to the speed of sound — which, underwater is 1,482 meters per second, or 3,320 mph, compared to fastest submarines that can only travel upto 30 knots while submerged. At that speed, you could go from Shanghai to San Francisco (about 6,000 miles) in well under two hours.
In their latest research Chinese researchers have removed the need to launch the submerged vessel at high speeds, approaching 100km/h, to generate and maintain the air bubble. The method described by the Harbin Institute of Technology in China uses a “special liquid membrane” that reduces friction drastically during low speeds. The membrane is constantly replenished as it gets worn down till the vessel reaches adequate speed, around 75km/h, and then appears to use the same gas-through-nose-cone technique to achieve supercavitation to create atmosphere bubbles.
Second, it has proved to be extremely difficult to steer the vessel using conventional mechanisms, such as a rudder, which are inside the bubble without any direct contact with water. As a result, its application has been limited to unmanned vessels, such as torpedoes, which were fired in a straight line because they had limited ability to turn. The organisation says that glass surface can conduct drag on one side or another to change directions and achieve easier cruising control.
The propulsion is another issue, new propulsion techniques possibly nuclear is required to be developed for longer range. Currently rockets only have enough fuel for a few minutes, limiting the range, the effective range of the Russian supercavitation torpedoes, for example, was only between 11 km and 15 km.
The article sources also include: