Cavitation Number Calculator

Cavitation is the formation of vapor bubbles in a liquid where local pressure drops below the liquid's vapor pressure, followed by the violent collapse of those bubbles when they move into a higher-pressure region. The collapse generates intense localized shock waves that can severely erode nearby surfaces over time.

The cavitation number, Ca, is a dimensionless quantity that compares the available pressure margin above a liquid's vapor pressure to the dynamic pressure of the flow. It predicts how likely a given flow condition is to trigger cavitation.

Ca = (p−p_v)/(½ρv²), where p is a reference (ambient or upstream) pressure, p_v is the liquid's vapor pressure at the operating temperature, ρ is fluid density, and v is a characteristic flow velocity.

There is no single universal threshold since it depends on the specific geometry, but generally a cavitation number below roughly 0.5 to 1 indicates meaningful cavitation risk, with lower values indicating progressively higher risk. Each specific device (pump, propeller, valve) typically has its own empirically determined critical cavitation number.

A liquid's vapor pressure rises sharply with temperature (it equals atmospheric pressure exactly at the boiling point), so hotter liquids have a smaller pressure margin before local pressure drops trigger vaporization, making cavitation more likely at the same flow velocity and reference pressure.

Cavitation is a major concern in centrifugal pumps (impeller erosion, reduced efficiency, noise), ship propellers (blade pitting, vibration, noise, the classic case that motivated much of cavitation research), control valves and orifices, and hydraulic turbines, anywhere fast-flowing liquid experiences local pressure drops.

Common strategies include increasing the available pressure margin (raising system pressure or lowering fluid temperature), reducing flow velocity at critical points, redesigning geometry to avoid sharp pressure drops (like blunt pump inlets or sharp valve edges), and selecting cavitation-resistant materials for components exposed to unavoidable cavitation.

NPSH is a closely related concept used specifically in pump engineering, essentially the same pressure margin idea expressed as a head (length) rather than a dimensionless ratio. Pump manufacturers specify a required NPSH, and keeping the available NPSH above this requirement is the standard practical way to avoid pump cavitation.

No, cavitation can occur anywhere liquid flow experiences a sufficiently large local pressure drop, including fast-flowing river water around obstructions, medical ultrasound and lithotripsy devices (which deliberately exploit cavitation), and even inside the human cardiovascular system in certain extreme conditions.

Collapsing cavitation bubbles can generate localized pressures and temperatures far exceeding the bulk fluid conditions (sometimes cited as thousands of atmospheres and thousands of degrees momentarily at the collapse point), producing a distinctive pitted, sponge-like surface damage pattern that differs from simple abrasive wear.