01 Sep 2002
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Modelling supercavitation using LS-DYNA finite-element software tool
When an object moves fast enough through water, the water vaporises and creates a cavity.
This effect has long been known to reduce the efficiency of marine propellors and to cause pitting damage when cavitation bubbles collapse against metal surfaces.
However, when the object moves even faster, then the cavity does not collapse, and may enclose part or all of the body which is creating it. This effect is known as 'supercavitation'.
Recent interest in supercavitation follows the 2001 sale of Russian 'Shkval' torpedos to China, and rumours that the August 2000 sinking of the 'Kursk' submarine involved a high-speed torpedo.
Supercavitation means that only a small area of the torpedo is wet, and the rest of the body is enclosed in a near vaccuum, dramatically reducing the skin-friction component of drag. This is what permits the high speeds, possibly hundreds of metres per second.
Torpedos are not the only application of supercavitation technology. Conventional ordnance, when fired through water, tends to become unstable. Stopping distances can sometimes be only a few metres. A better understanding of supercavitation might lead to more effective designs for applications such as surface mine elimination.
Modelling supercavitation is an extremely challenging free-surface problem for classical hydrodynamics and Computational Fluid Dynamics (CFD) codes. An ATC 'LOOKout!' project is currently underway in collaboration with BAE SYSTEMS Underwater Weapons Division and Royal Ordnance. We are addressing the design of supercavitation devices by using a wide variety of tools, such as potential flow, Euler-Lagrange methods, Smoothed Particle Hydrodynamics (SPH) and CFD.
