supercavitation

Supercavitation is a hydrodynamic phenomenon in which a body moving at high speed through a liquid creates a large vapor-filled cavity, or bubble, that surrounds most of the object. The cavity minimizes contact with liquid, reducing drag and permitting speeds unattainable by conventional underwater vehicles. The effect arises when local pressure around the object's surface falls below the liquid's vapor pressure, causing cavitation and the formation of vapor within the cavity. If the cavity is sufficiently large and stable, the object travels primarily inside the low-density vapor, dramatically reducing wetted surface area.

Formation and stability: Achieving a supercavity requires high initial speeds, specialized nose geometry, and often gas injection to seed and stabilize the bubble; the cavity expands downstream and must be maintained; factors include fluid properties, surface tension, and turbulence; cavities can be interrupted by external disturbances, collapse, or re-contact with liquid, causing rapid drag increase and potential thermal and mechanical stress.

History and applications: The most well-known practical implementation is the Soviet Shkval torpedo, developed during the late 20th century, which reportedly achieves very high speeds by enclosing the body in a gas/vapor cavity. Other research has explored supercavitation for high-speed underwater projectiles and potential missile concepts; ongoing work addresses maneuvering inside a supercavity, cavity shaping, and erosion and noise challenges.

See also: Cavitation, bubble dynamics, undersea propulsion.