Numerical theory and method on the modal behavior of a pump-turbine rotor system considering gyro-effect and added mass effect

The pump-turbine unit is the core equipment of pumped storage power station, and the rotor system is the key component of the pump-turbine unit. In this paper, the numerical method considering the gyro-effect and added mass effect is proposed, the effect of the added mass, gyro-effect and bearing stiffness are discussed, respectively, and a "transfer" phenomenon of the mode shape is found. A coupling influence coefficient is proposed to analyze the coupling influence of gyro-effect and added mass effect on the rotor system mode, and the nodal diameter (ND) mode of runner is discussed. For the forward whirling ND mode, the coupling influence coefficient increases with the increase of the rotational speed, while for the reverse whirling ND mode, the coupling influence coefficient decreases with the increase of the rotational speed. The results in this paper can provide a theoretical basis for revealing the complex dynamic behaviors of the rotor system, and provide scientific guidance for the research and development, design, and safe and stable operation of pump-turbine units.