Numerical investigation of the effect of the closure law of wicket gates on the transient characteristics of pump-turbine in pump mode

Abstract

Two kinds of two-stage broken line closure laws of the wicket gates, modified A scheme (MAS) and modified B scheme (MBS), are presented to investigate the relationship between the wicket gates closure law and pressure pulsation shutting down pump turbines. The Detached Eddy Simulation (DES) model that is based on the moving mesh technology, is adopted to simulate the process of closure of the wicket gates. The results are analyzed in the time-domain and the time-frequency domain by Continuous Wavelet Transform (CWT). It was discovered that at the vaneless space, there isa intense pulsation at Blade Passing Frequency (BPF) lasting up to 3s in the original scheme (OS) of linear closure law, while the duration is reduced by 16.17% in MAS and has little change in MBS. At the leading edge of the stay vane, the high amplitude pulsation lasting nearly 1s is observed in OS. However, this pulse duration is reduced by 50% in MAS. Interestingly, in MAS, there is also a stabilization period lasting 1s before the wicket gates are fully closed, which is consistent with the pressure characteristics at the outlet of wicket gate. Moreover, the BPF and low frequency are the main components in the time-frequency plots. And the fluctuation energy at BPF and low frequency in the MAS is significantly smaller than the other two schemes. It is important that the torque duration at BPF is significantly reduced by 35% in MAS and slightly reduced in MBS. It is worth noting that the closure law of wicket gates has great effect on the pressure pulsation at BPF. This study is crucial improving the transient characteristics of pump turbines in pump mode by using the two-stage broken line closure law.