Investigation of Energy Loss Mechanisms in a Pump-Turbine Under Different Guide Vane Openings in Pump Mode Based on Entropy Production Theory

To address the unclear flow regime variations and energy loss mechanisms of pumped-storage units operating under variable loads with different guide vane openings in pump mode, this paper conducts a refined quantitative investigation into the internal flow field structures and energy dissipation mechanisms of a pump-turbine under three typical guide vane openings. The methodology is based on the SST k-ω turbulence model and entropy production theory. The results demonstrate that the guide vane is the most critical component inducing the macroscopic head loss of the unit, and its energy dissipation is quantitatively dominated by turbulent entropy production induced by mainstream vortex dynamics, while localized direct viscous dissipation intensifies sharply near high-shear throat boundaries under throttled regimes. In the low-flow-rate region, large-scale high-entropy production areas emerge across all openings due to the incidence angle mismatch. As the flow rate increases, these high-dissipation areas gradually shrink. Upon entering the high-flow-rate region, the high-entropy production area at the leading edge of the guide vanes under the small opening condition dramatically rebounds and expands, which is attributed to the severe flow blockage effect. In contrast, under the large opening condition, the high-entropy production regions are essentially eliminated owing to the superior flow passage capacity. This study systematically analyzes the spatial distribution and variation laws of irreversible energy losses across a wide operating range with multiple openings, revealing the intrinsic correlation between internal flow regimes and microscopic thermodynamic dissipation. The findings provide a crucial theoretical reference for the wide-load efficient operation scheduling and anti-stall hydraulic optimization design of pumped-storage units.