Cavitation resistance in rotodynamic pumps

Cavitation is manifested by the formation of a variety of vapor structures within the flow, depending on operating conditions and the design of the interbore channels. These cavitation patterns appear in low-pressure zones and are transported to high-pressure zones, where they implode. The harmful consequences of cavitation are diverse: erosion, characteristic noise, operating instabilities, drop in performance...

The study of cavitation continues to mobilize the energies of many researchers, as several phenomena at different levels interact within a flow undergoing cavitation: molecular, thermodynamic, hydrodynamic, hydroacoustic, mechanical and vibratory, fluid-structure interaction, etc.

Cavitation is an extremely unstable phenomenon involving a highly compressible liquid/vapor mixture, where the two phases move at different speeds and are separated by interfaces with surface tensions, where mass and momentum exchanges are permanent. Moreover, phase changes (vaporization and condensation) occur violently, and the mechanisms for generating, transferring and dissipating turbulence in the mixture are different from those observed for a homogeneous liquid. Finally, changes of state are associated with heat exchanges between phases, which modify the vaporization pressure of the liquid, thus delaying the onset of cavitation. This thermodynamic effect is particularly significant in the case of heat-sensitive fluids.

We're looking into these physical phenomena in greater depth, in order to limit their undesirable effects, particularly on rotodynamic machines and pumps in particular.

In these machines, the appearance of cavitating pockets, their geometry and, more generally, their static and dynamic properties depend on numerous parameters: the profile of the blades, their camber, the way they are stacked, the incidence of the upstream flow, the pressure level, turbulence at the inlet, the existence of dissolved gas microbubbles, the roughness of the walls, etc., all play a part in the appearance, development and effects of cavitation.

The aim of this article is to provide tools for characterizing and assessing the level of cavitation in rotodynamic pumps, and possibly delaying its onset and development, as well as reducing its effects. Another important objective is to provide design criteria for improving impeller layouts and minimizing adverse effects.