Abstract: Acoustic fluid-structure coupling has obvious influence on pump-turbine runners due to their flat structure, and the natural frequency is greatly lowered in working channel. In addition, the hydraulic excitation in the start-up and shut-down processes of the unit could lead to the resonance of the runner. Therefore, it is necessary to carry out modal analysis of the runner to ensure its safety and stability during operation. This paper adopts an acoustic fluid-structure coupling method to analyze the modes of the runner, taking the added fluid mass outside the runner entity in consideration. We change the diameter and height of the runner, and examine the effect of the ratio of the diameter to height of the runner on its working mode. Results show that the effect of added mass from fluid is in a decreasing order of upper clearance, lower clearance, and inner channel. We also find that, as the ratio of the runner diameter to height decreases, the natural frequencies of the runner increases, but the added mass effect decreases. The results can help evaluate the runners’ vibration and resonance characteristics, and therefore are instructive on predicting the runner safety of large pumped storage units.

Key words: pump turbine, runner, acoustic fluid-structure interaction, modal analysis, resonance