Visualization research of energy dissipation in a pump turbine unit during turbine mode's starting up

Identifying the precise location of flow energy dissipation (FED) in pump turbines is crucial for enhancing the stability of pumped storage power stations. In this study, the transient process of the turbine mode's starting up in the pump-turbine has been simulated to examine the FED locations by using the one-dimensional and three-dimensional (1D-3D) coupled computational fluid dynamics (CFD) method. This analysis pinpoints high FED locations in each component of the pump-turbine. The observations reveals that the trailing edge of the guide vane consistently demonstrates high FED values, while wall shear stress, axial and radial forces had a significant effect on flow characteristics. Moreover, high FED sites correspond to high turbulence kinetic energy locations. Continuous wavelet transform (CWT) has been applied to examine the time-frequency characteristics during this process. Low frequency (fc = 0.12) has been identified as the dominant frequency in the volute. In the draft tube, the wavelet magnitude of the double blade passing frequency (fc = 18) is 30.4% of that under the dominant frequency (fc = 9). Regional visualization of FED offers a valuable method for the in-depth understanding of energy dissipation in pump turbines and improving operational stability in pumped storage power stations.