Evaluating the pressure fluctuations during load rejection of two pump-turbines in a prototype pumped-storage system by using 1D-3D coupled simulation

Abstract

Load rejection is one of the dangerous transient scenarios in pumped-storage power stations (PSPSs), and the risk should be evaluated from design to operation stages of PSPSs. In this study, the extreme case with simultaneous load rejection of two pump-turbines in a prototype pumped-storage system was simulated by using the one-dimensional and three-dimensional (1D-3D) coupled computational fluid dynamics (CFD) method. The aims are to evaluate the risk of pressure fluctuations during this scenario comprehensively and assess the feasibility of the newly developed 1D-3D coupled approach in engineering applications. The results show that the maximal pressures (superimposed by water hammer and pulsating pressures) upstream of the runner exceed the industry standard. The largest maximal pressure and the longest overpressure duration occur in the vaneless space and are caused by the strong rotor-stator interaction (RSI). The strong RSI may be attributed to the unevenly distributed high gradient regions of pressure aroused by the uneven radial velocity pattern with obvious reverse flow at the runner inlet. This attempt revealed the mechanism of severe pressure pulsations during transient processes and demonstrated that the 1D-3D coupled method is feasible for engineering applications, especially in evaluating the transient risk of new ultrahigh-head PSPSs.