The supercavitation is the use of the effects of Cavitation to create a large bubble of Gaz inside a Liquide, making it possible an object to travel to large Speed in this liquid while being completely wrapped by the bubble. The cavity (i.e. the bubble) reduced friction on the object and makes supercavitation a very attractive technology and due: friction in the Eau is approximately: 1000 times larger than in a gas like the Air, which in this case is Steam. The supercavitation is studied enough in Magnétohydrodynamique (MHD).

Cavitation with the supercavitation

Cavitation is a known phenomenon. It occurs when a liquid is forced to move at high speed, for example inside a pump or around an obstacle. The Pression of the fluid drops because its high speed (Principe of Bernoulli) and when the pressure of the liquid falls below the pressure of vaporization, it vaporizes - typically by forming small steam bubbles, i.e. of water in its gas form. In Hydrodynamic ordinary, cavitation is a phenomenon which, most of the time, is fortuitous and undesirable: usually, the bubbles are not constant but implosent because of the sudden deceleration of the fluid, with a sudden rise in the environmental pressure. These small implosions can even lead to physical damage, for example with a Hélice very fast evil conceived.

An object in supercavitation employs this phenomenon of a way much larger and more supported, from where the name. The principal characteristics of an object in supercavitation are a nose particularly worked, in general flat with pointed edges, and a shaped form Hydrodynamique and Aérodynamique. When the object travels in water at raised speeds, the nose so much quickly draws aside water towards the outside which it steals free of surface. The pressure of water takes time to fill the space of the cavity which results from it, consequently the nose opens a long steam bubble. With sufficient speed, the cavity can be prolonged to wrap the whole body of the object. An object in supercavitation " vole" literally in surrounding gas.

Officially, in 1977, the Engineer S Soviet S developed the first projectile to be used the supercavitation: a Torpedo VA-111 Shkval. This one can travel to 100 m/s in water, that is to say 35 m/s moreover than the conventional torpedes. Still faster speeds of approximately 140 m/s and more were also reported. However if the projectile gains of speed, this kind of torpedo loses of handiness because they oblige with a direct shooting (right) on the target; they cannot transfer as the traditional torpedes because that would break the bubble.

The trail of an object (and thus the force necessary to propel it) is proportional to the density (or density) of the fluid in which it moves. The density of liquid water being much more important than that of the steam, with a similar force of push, the torpedo thus moves much more quickly.

One proposed various underwater methods of propulsion to reach speed necessary. The concept best adapted being seems an engine of rocket burning of the Aluminum with water. However, a conventional engine of rocket is used to propel the Torpille to supercavitation " Shkval ".

The the United States of America and the Great Britain also have similar torpedes with supercavitation.

Current applications

The principle of supercavitation is employed for engines of very high output and also for control surfaces and rudders. Until 2004, the Russian torpedes of Shkval were the only publicly known application of the technology of supercavitation applied to a whole sinkable object. It was reported that the Russia also has the underwater firearms drawing from the projectiles with supercavitation which would have been developed before the Shkval torpedes. The construction of such machines remains a secrecy jealously defended by the armies but in the case of Shkval, one knows that the nose of the projectile is relatively flat and that the body of the weapon has several wings intended to stabilize it. Moreover, the torpedo sends part of the gases which escape from its conduits in direction of its nose. That makes it possible to maintain a bubble stable with the adequate form. This type of weapon could be at the origin of the shipwreck of the Sous-marin Koursk .

In 2004, the German manufacturer of weapons DIEHL BGT announced its own torpedo with supercavitation called Barracuda which would reach a speed of 800 km/h.

Beginning 1994, the American navy started to develop a system of destruction of mine S underwater known under the name of " RAMICS" ( Rapid Airborne Undermines Clearance System ), based on a projectile with supercavitation stable in the air and the water and invented by C Tech Defense Corporation . RAMICS is currently under development final before the introduction into the active fleet.

In 1999, the technology of supercavitation was adopted with the projectiles of hunting. These balls " SuperPenetrator" keep a very stable straight line after penetration in an aqueous medium.

Up to now, research on the supercavitation was mainly undertaken for the development of Torpille S.

External bonds

• Article on the supercavitation and the torpedo Barracuda: pages 1 2 3 4.