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 (VMD), 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.