An Engineering Case Study on Vortex-pressure Linkage in Clearance Flow and the Induced Abnormal Vibration of a High-head Pump-turbine

Abnormal head-cover vibration is a persistent problem in high-head pump-turbines. A hydropower station in China installed crown bosses on the runner crown to mitigate such vibration. Field tests showed that the vibration intensified after the modification. This study combines SST-DES simulations with field tests to trace the full mechanism chain from the boss geometry through vortex dynamics and pressure spectrum reconstruction to the vibration response. The 26.6-degree boss turning angle reshapes the pressure spectrum in two opposing ways. In the downstream seal and outlet regions, pressure fluctuation amplitudes are reduced, with an average vorticity attenuation of 42.3% in the labyrinth seal. In the upstream inlet and development regions, the blade-passage frequency is enhanced, the 82.97 Hz discrete peak is eliminated, and low-frequency broadband energy below 50 Hz becomes dominant. Small-scale high-frequency vortex structures are replaced by large-scale low-frequency coherent structures. A pressure component near 195 Hz emerges post-modification and falls within the head cover natural frequency band of 194 to 196 Hz, with a 149% amplitude increase. The dominant vibration frequency shifts from 146 Hz to 183 Hz. These findings indicate that the current boss configuration is not a viable mitigation strategy for the unit studied. The vortex-pressure correlations identified in this work can inform future clearance passage designs that target specific frequency bands.