Numerical and experimental study of structural vibrations in pump turbines

As a critical component for power system peak load regulation and frequency control, the stability and reliability of the water pump turbine are crucial. However, the issues of unit vibration caused by unstable flow in water pump turbines have not been comprehensively understood and systematically summarized to date. Therefore, a numerical and experimental study was conducted to investigate the structural vibrations of the water pump turbine (HLD307-LJ-150 model), a part of the world's first hydro-solar combined power generation system. The research focused on analyzing rotor dynamic response, stress modal analysis, and bearing vibration issues. Key findings revealed that the turbine operates most efficiently with guide vane openings between 45 % and 75 %, achieving peak efficiencies of 91.9 % (130 m head), 91.12 % (140.5 m head), and 90.71 % (161 m head) at guide vane openings of 65 %, 65 %, and 55 %, respectively. Under low load conditions, severe flow separation and vortex formation led to an efficiency drop to 58.92 %. Modal analysis indicated minimal impact of prestress on the natural frequencies of the rotor, with the first six modes ranging from 238.77 Hz to 562.55 Hz. Structural deformation was primarily concentrated in the lower ring and adjacent blade regions, with stress increasing proportionally with head and output (such as the rated head of 376.2 kPa). Pressure pulsation analysis identified the dominant frequency as 20 times the rotational frequency (20fn = 166.6 Hz), reaching amplitude peaks of 102.84 kPa under partial loads. Experimental data confirmed higher vibration amplitudes (up to 120 μm) and speeds (15 mm/s at 920 rpm) for radial bearings compared to combined bearings, necessitating reinforced stability measures. These results provide crucial insights for optimizing pump turbine designs to mitigate vibrations and enhance operational stability, while providing theoretical guidance to enhance the reliability of hydro-solar interactions. • The research subject is the world's first water-electricity complementary pumped storage unit. • The problems of flow-induced vibration and deformation of the unit were studied. • The experiment measured the vibration velocity and amplitude of the unit at different rotational speeds. • The numerical research method of fluid-structure coupling was applied to reveal the deformation mechanism induced by flow.