Abstract: During the transportation of thermo-sensitive fluids such as liquid hydrogen and liquid nitrogen, unsteady cavitation is prone to occur at the inlet of high-speed centrifugal pumps, which poses a serious threat to operational safety. To reveal the evolution of unsteady cavitation and the associated mechanism of energy dissipation, this study combines experimental measurements with numerical simulations. A visualization test platform for cavitating flows in a high-speed centrifugal pump was established, and high-speed imaging was used to capture the evolution of cavitation patterns of a thermo-sensitive fluid (LM-8 refrigerant) under various operating conditions (flow rate, rotational speed, and inlet temperature), while the external performance of the pump was measured simultaneously. In the numerical study, an unsteady cavitation model considering thermodynamic effects was developed, and a two-phase entropy production diagnostic method was introduced to quantitatively analyze local irreversible energy dissipation during the cavitation process. The results show that with increasing flow rate, the cavitation region shrinks and the critical net positive suction head (H_NPS) increases, but the head decreases due to turbulence-induced disturbances; as the rotational speed increases, the head and cavitation coefficient increase, and the cavitation pattern evolves from a multiregion cloud-like structure to a single-region sleet-like structure; with increasing inlet temperature, the saturated vapor pressure rises, causing cavitation to occur at higher H_NPS values and making the process more intense. Entropy production analysis reveals that interfacial phase-change entropy and turbulence-induced fluctuation entropy are the main sources of the total energy dissipation. When the rotational speed increases from 2 100 r/min to 3 500 r/min, the proportion of interfacial entropy production rises sharply from 2.27% to 54.3%, while the total entropy production increases from 1 815 W/K to 56 002 W/K. These findings provide theoretical support for the optimization and fault diagnosis of high-speed centrifugal pumps in aerospace, nuclear energy, and other fields.

Key words: high-speed centrifugal pump, thermo-sensitive fluid; cavitation visualization, unsteady flow, numerical simulation, entropy production diagnosis