Mingkun Fang

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.

Disk friction loss is remarkably significant in low specific speed centrifugal pumps, originating from the complex flow interference within the rotor-stator cavity. To reveal the hydrodynamic mechanism and energy dissipation characteristics of this loss, this study investigates the flow in the rotor-stator cavity under leakage flow conditions by combining experimental measurements with numerical simulations using the Shear Stress Transport (SST) k–ω turbulence model. Furthermore, Entropy Production Theory is introduced to quantify the spatial distribution of energy losses. The results indicate that a typical toroidal vortex structure exists within the cavity, and its morphological evolution directly governs the circumferential velocity in the potential core. Entropy production analysis further reveals that the energy dissipation is primarily composed of mean flow viscous dissipation near the walls and turbulent dissipation within the vortex core region. This study elucidates the loss mechanism of clearance flow from a thermodynamic perspective, providing a theoretical reference for the drag reduction design of low specific speed pumps.

In this study, an analysis of a low-specific-speed pump is carried out based on the methods of one-way and two-way fluid–structure interactions (FSIs). This study analyzes the influence of FSIs on the internal flow field and external characteristics of the pump. Utilizing a two-way FSI, the signal coherence analysis method is employed to analyze the coherence of signals between the flow field and the structural field. Addressing the issue of a lack of a connection between the two signals, this study bridges a gap in the existing research. The results indicate that different interaction methods have certain influences on impeller stress and deformation. However, in both coupling modes, the maximum deformation and the maximum equivalent stress have the same distribution position. The head error obtained using the two-way coupling method is lower than that of the uncoupled results, which indicates that the two-way FSI calculation results are closer to the experimental results. The pressure pulsation signals at the interface of the impeller and volute exhibit strong coherence with the structural field signals. For low-specific-speed centrifugal pumps, establishing a clear connection between the flow field signals and structural field signals will help guide further optimization of their performance through design.