Pressure fluctuations during the pump power-trip of a low-head pump-turbine with the co-closing of guide vane and ball valve

Abstract

The pressure fluctuations (PFs) were significantly different for different head pump turbines (PTs). To study the evolutionary mechanisms of PFs inside a low-head PT, the co-closing of the guide vane (GV) and ball valve after a pump power trip was simulated by adopting the one- and three-dimensional coupled approach and dynamic mesh technology. Additionally, the simulation results were validated through comparison with the experimental data. The results suggest that the transient performance and pressure fluctuate severely before the PT passes through the reverse maximum flowrate condition, which causes severe fluctuations in the impeller radial hydraulic thrust (FR). Moreover, the study found that PFs during the transition of low-head PTs also include two new frequency components, fDV caused by the Dean vortices in the spiral casing and the 38–40-fold impeller-rated rotation frequency caused by the periodical interactions between the rotational impeller and the regular high-pressure (HP) regions in the stay/GV, in addition to the frequency components fRSI-S and fRSI-R caused by rotor-stator interactions and fBFV caused by local backflow vortexes close to the impeller inlet. The two new fluctuation frequency components cannot be captured for the middle-head and high-head PTs and primarily influence the axial hydraulic thrust of the impeller (FZ). This finding can provide an important theoretical guide for the design and optimization of low-head PTs.