Cavitation-induced evolution of unsteady flow structures and energy dissipation mechanisms in a multistage liquid-cooling pump

Abstract

Rising heat-flux densities in high-performance computing centers impose stringent requirements on the stability of liquid-cooling circulation systems, in which centrifugal pumps are susceptible to cavitation-induced flow instabilities. However, the physical mechanism by which cavitation disturbances are generated and attenuated in multistage liquid-cooling pumps remains unclear. In this study, unsteady cavitating flow in a three-stage liquid-cooling pump under the rated flow condition is numerically investigated using variational mode decomposition, rigid-vorticity identification, and entropy production analysis. The results reveal that cavitation does not uniformly amplify pressure pulsations; instead, it selectively enhances rotational-frequency disturbances. This amplification is strongest at the inlet of the first-stage impeller and gradually attenuates downstream, indicating a first-stage-dominated instability mode. The underlying mechanism is associated with the coupling among leading-edge cavitation evolution, suction-vortex-induced inlet flow distortion, and blade-sweeping effects. Periodic cavity growth, shedding, and collapse modify local pressure and velocity gradients, while suction vortices periodically vary the incoming flow angle during blade passage. This coupled process intensifies shear, recirculation, and flow separation near the first-stage impeller inlet, thereby increasing rotational-frequency disturbances. Entropy production analysis further shows that the hydrodynamic irreversible losses under cavitating conditions are mainly concentrated in the first-stage impeller and diffuser, with limited influence on subsequent stages. These findings identify the first-stage impeller inlet and suction-side leading edge as critical regions for suppressing cavitation-induced unsteady disturbances and energy loss in the investigated pump under the rated flow condition.