Kavitation

Kavitation is the phenomenon in which vapor-filled cavities form in a liquid when local pressure falls below the liquid’s vapour pressure. These cavities can grow and then collapse violently as surrounding pressure increases, producing shock waves and microjets. The effect is most commonly observed in fast-moving fluids or in liquids subjected to intense acoustic fields.

Kavitation occurs mainly in two forms: hydrodynamic cavitation, driven by rapid changes in pressure within a flowing liquid (such as through valves, nozzles, or around propeller blades); and acoustic cavitation, produced by high-intensity sound waves that create alternating low- and high-pressure regions. In both cases, bubble nucleation and collapse can generate extreme localized conditions, including high temperatures and pressures for very short times.

The consequences of cavitation are mixed. It can cause material damage through pitting and erosion of pumps, turbines, propellers, and piping, reduce efficiency, increase vibration and noise, and shorten component life. Conversely, cavitation can be leveraged for beneficial purposes, such as ultrasonic cleaning, emulsification, sonochemistry, and water treatment. In medicine, controlled cavitation underlies some therapeutic techniques and diagnostic methods, including contrast-enhanced ultrasound and certain stone-fragmentation procedures.

Measurement and control of cavitation focus on avoiding unwanted onset in mechanical systems and exploiting it where useful. Design strategies include increasing suction head or reducing flow speeds to raise local pressure, smoothing flow paths, or operating at conditions above the cavitation threshold. Detection methods include acoustic monitoring, high-speed imaging, and investigations of pressure fluctuations.