Study on Internal Flow Characteristics and Pressure Pulsation Features of Pump-Turbine under the no-load Startup Condition with Different Heads

Abstract Unstable operation during the no-load startup of pumped storage hydroelectric power plants is a significant factor affecting the successful grid connection of units. To investigate the internal flow and pressure pulsation characteristics during the no-load startup of pump-turbine under varying heads, the vertical single-stage mixed-flow reversible pump-turbine is studied. Numerical simulations are performed using the SST k-ω turbulence model, and the Fast Fourier Transform (FFT) method is employed to analyze the pressure pulsation signals. A comparative study is conducted on the pressure pulsation characteristics and internal flow features at different positions under various heads. The results indicate that the pressure pulsation in the draft tube cone region is the most severe, with the dominant blade passing frequency ( f BPF ) and its harmonics caused by rotor-stator interaction (RSI) in the spectra of pressure pulsations at various heads in the draft tube cone region. Additionally, the pressure pulsation amplitude increases as the head decreases, while low-frequency pulsation signals are prevalent throughout the entire flow passage. Compared to the flow condition, the influence of rotor-stator interaction on pressure pulsation is more significant. During the no-load startup at the highest head, the pump-turbine exhibits the most vortex structures and the poorest flow condition, while the intensity of pressure pulsation in the draft tube cone region is the lowest. These research findings provide a basis for the stable no-load startup of pump-turbine.