5. 3D cavitating flows

The phenomenon of cavitation in turbomachinery with incompressible fluids is due to the vaporization of the fluid being conveyed when, locally, its static pressure becomes equal to its saturation vapour pressure. Any acceleration of the fluid, such as bypassing a leading edge, narrowing a cross-section, rotating or swirling, causes a reduction in static pressure. Cavitation is manifested by the formation of various vapour structures within the flow, depending on the operating conditions and the design of the machine, be it a pump or a hydraulic turbine. These cavitation patterns appear in low-pressure zones and are transported to high-pressure zones. Under the action of the pressure gradient, the steam bubbles implode as soon as the local pressure exceeds the steam pressure.

Cavitation has a number of harmful consequences:

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