Gap Vortex Evolution and Vibration Excitation Characteristics of a Pump-turbine under Dump-load Conditions

This study examines the evolution mechanism of gap-vortex structures and the corresponding vibration excitation under load-rejection conditions in a pump-turbine. Through numerical simulations, we systematically investigate the flow characteristics, vortex dynamics, and pressure pulsations within the clearance region of a pumped-storage unit. The results show that the gap flow transitions from an initially quasi-steady state to a multi-scale unsteady pattern, displaying coupled effects of shear enhancement, flow redistribution, and vortex-induced instability. In the upper crown region, the vortex core develops from localized small-scale disturbances into band-like structures during the early stage, eventually forming concentrated fluctuations in the later phase. In contrast, the lower ring region exhibits more pronounced three-dimensional evolution accompanied by a delayed dynamic response. Spectral analysis of pressure pulsations indicates a gradual broadening from low-frequency dominance to a wideband distribution. The principal frequency component corresponds to the rotor’s low-order modal frequency (۱.۷۸ fn), implying a potential structural-resonance risk. The emergence of multi-frequency and non-integer harmonic components further reveals complex nonlinear excitation mechanisms and multi-region coupling effects, which may generate intermittent shock-type fluctuations in the local flow field and act as a key source of hydraulic excitation. These findings provide important insights into flow instability and vibration response under load-rejection conditions and offer valuable references for structural optimization and vibration-control strategies in pump-turbine systems.

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">Pump-turbine ، ، ">Interstitial flow ، ، ">Load-shedding process ، ، ">Eddy ، ، ">Hydraulic excitation