Time-frequency characteristics and mechanisms of pressure pulsations in a pump turbine during the turbine start-up transients

Abstract

During turbine start-up (TSU), various complex flow phenomena inside the pump-turbine affect the unit stability. The stability of TSU is crucial for successful grid connection of the unit. In this study, a governor equation was introduced, and a one- and three-dimensional coupled computational method was employed to simulate the dynamic variations in the guide vane (GV) opening during TSU. This method achieved a high-precision simulation of the TSU process, eliminating the use of oversimplified linear GV variations as a substitute for dynamic GV opening variations. Furthermore, the short-time Fourier transform method was used to conduct a time–frequency analysis of the pressure pulsations (PPs) during TSU. This study identified a novel PP component with the same waveform as that of the GV opening and flowrate variation curves. This PP component was induced by a fluid whose direction was altered by the blade leading-edge collision. Its frequencies are related to the rotational speed, manifesting as high and low frequencies during low-speed and high-speed TSU processes, respectively. These findings provide valuable references for the selection of governor parameters for the TSU process.