Effect of temperature on gas–liquid two-phase flow characteristics in a pump as turbine

This study numerically investigates the cavitation behavior and gas–liquid two-phase flow dynamics in a Pump as Turbine (PAT) under varying temperature conditions. The results demonstrate a nonlinear and threshold-dependent thermal effect on PAT performance. A critical temperature of 70 °C was identified, beyond which the steam volume fraction exhibits exponential growth. At 90 °C, this results in a 38% head loss and a 2.4% torque reduction compared to 80 °C. Spatially, cavitation intensifies heterogeneously, preferentially concentrating near the trailing edge of the blade. Analysis of the underlying mechanisms reveals that the temperature-enhanced cavitation triggers a strong cavitation–turbulence coupling, serving as an additional energy source that amplifies turbulent kinetic energy and significantly increases entropy production, accounting for the irreversible energy loss. Furthermore, a distinct thermal sensitivity in impeller forces is uncovered. While radial force remains stable, axial force exhibits a pronounced dependence, peaking at high temperatures due to a cavitation-altered blade pressure distribution. In summary, this study elucidates the thermo-fluid-mechanical coupling mechanisms governing PAT performance under thermal loads, providing critical insights into the optimal design and operational stability of PATs in high-temperature environments.