Research on the Three-dimensional Transient Characteristics of the Hydraulic System during Load Rejection with Combined Regulation of Ball Valve and Guide Vanes in the Entire Hydraulic Passage of the Pumped Storage Power Stations

The complex transient flow field in the entire hydraulic system of a large pump turbine under load rejection conditions, involving the simultaneous closing of the ball valve and guide vanes, is comprehensively investigated using the Re-Normalization Group (RNG)k-e model and Fast Fourier Transform (FFT) technique. The predicted pressures at the volute inlet and guide vane outlet show good agreement with the field test data, with corresponding relative errors of ۰.۸۷% and ۰.۳۳%, respectively, between the predicted maximum pressures and those measured in the field. The main frequencies of pressure at the volute inlet are the unit rotating frequency during the initial time stages (۰–۳s), and low-frequency fluctuations in the later stages (۳–۸s and ۸–۱۱s). In contrast, the corresponding frequencies at the guide vane outlet are consistent with the blade frequency. During the ball valve closing process, as the unit rotational speed increases, complex flow separations cause vortices near the middle of the runner to coalesce into two large vortices of similar size. Meanwhile, the cross-sectional area of the vortex rope in the draft tube increases, and its spiral shape becomes increasingly irregular until it breaks apart. Based on the Q criterion, a series of ۳D complex vortices form inside and downstream of the ball valve at the onset of the combined closing stage, intensifying as the guide vanes close. A spiral-shaped vortex rope in the draft tube extends downstream, breaking into smaller vortices after passing through the draft tube elbow, with the location of the fracture moving upstream as the flow rate decreases further.

کلیدواژه ها:

Combined regulation ، Load rejection ، Pump turbine ، Q Criterion ، Vortex