Numerical analysis of pressure fluctuations in hump region of a pump-turbine

Abstract To reveal the pressure fluctuation characteristics in hump region of a pump-turbine, unsteady simulation for the whole flow passage, based on the SST k-w model, was performed on a pump-turbine model. This study analyzed the time-frequency characteristics and variation laws of pressure fluctuations in different flow passage components, and explored the relationship between pressure fluctuations and internal flow in the vaneless space, guide vane and draft tube. The results indicate that pressure fluctuations in the vaneless space primarily include the blade passing frequency of 7 fn and its harmonics, and a low-frequency component of 0.15 fn caused by rotating stall. Particularly, rotating stall has the greatest impact on pressure fluctuations in the guide vane. As the flow rates decreased, flow separation intensified and pressure fluctuations increased gradually. The frequencies of pressure fluctuations in the runner include runner rotation frequency of fn and its harmonics, rotor-stator interaction frequency of 20 fn , and others related to internal vortices (1.45 fn and 2.9 fn ). In the guide vane, spiral casing, and draft tube, the dominant frequencies were low-frequency components of 0.15 fn and 0.1 fn , and its amplitude in the spiral casing and draft tube was approximately 5% and 10% of that in the guide vane.