Effect of Geometric Parameters in the Seal Clearance on the Modal Characteristics of Pump-Turbine Runner

The runner of a pump turbine features a relatively flat structural configuration. The clearance cavities formed between the upper crown, lower band, and surrounding stationary components play a critical role in its dynamic behavior and operational stability. Consequently, a detailed modal analysis of the runner is essential to ensure safe and stable operation. In this study, an acoustic–structure coupling method is adopted to investigate the wet modal characteristics of the pump-turbine runner, explicitly accounting for the added mass effect induced by the fluid in the external flow passages. By systematically varying the geometric parameters of the upper crown clearance cavity, the influence of seal clearance dimensions on the runner’s modal characteristics is examined. The results demonstrate that the radial clearance and the axial height of the seal cavity are the most influential parameters, reducing natural frequencies by up to 15.85% and 16.93%, respectively. The pitch of the seal teeth shows a secondary yet notable effect, inducing a frequency variation of 13.73%. In contrast, local labyrinth seal parameters, such as the number of teeth and tooth width, have a comparatively limited effect. This study provides practical guidance for vibration risk prediction, anti-resonance design, and operational stability assessment of high-head, large-capacity turbine runners by revealing the quantitative relationship between geometric parameters and modal frequencies.