Flow-induced vibration analysis in a pump-turbine runner under transient operating conditions

The dynamic characteristics of the pumped storage unit (pump-turbine runner) make it highly susceptible to vibrations. Previous studies seldom addressed the clearance variation due to runner vibration, largely because of two challenges: the integration of the moving grid with the clearance and governing equations, and the intricacy of factoring in the entire shaft system's influence on vibration. By employing user-defined functions (UDF), kinematic equations for the pump-turbine runner's rotation and translation were formulated and integrated with computational fluid dynamics results. This paper introduces a computational method to simulate clearance-induced vibration displacement. The study examines the impact of clearance vibration displacement on the pump-turbine's transient flow field and runner vibrations under various operating conditions. Notably, deviations from the rated load condition led to an expansion-contraction trajectory of the runner axis, culminating in chaotic behaviour in the "S" characteristic zone. The correlation between runner vibrations and pressure fluctuations strengthened with the clearance displacement model, especially in narrow labyrinth seal clearances. Simulations also provided a refined estimation of the secondary rotational speed increase during load rejection. The method's reliability is confirmed through field test data comparison, offering a fresh perspective to identify the vibration characteristics of the pump-turbine runner.