FLUID-STRUCTURE INTERACTION ANALYSIS FOR RESONANCE INVESTIGATION OF PUMP-TURBINE RUNNER

In the development of high head pumped storage projects, one of the critical problems is the strength of pump-turbine runners. In this paper, the analysis method of forced response of the runner structure is presented and the prediction accuracy is validated by comparing with the results of the prototype head model test. And the application results for resonance of pump turbine startup process are shown. Basically it is necessary for the prediction of the runner dynamic stress to use a combined approach of fluid dynamics and structural dynamics. Due to the high complexity of the phenomena and the limitation of computer power, the numerical simulation for the fluid-structural interaction phenomena was in the past too expensive and not feasible. However, due to consideration that vibration displacement is very small, such complex analysis has been handled as one-way fluid-structural interaction problem. Namely the excitation force is calculated by whole passage flow analysis that is ignored the structural deformation and takes into account the rotor-stator interaction effect. And the dynamic stress of runner is calculated by the transient response analysis taken account into the added mass effect of surrounding water using an acoustic fluid formulation. Due to such a simplification, it has been possible to evaluate the runner dynamic stress in a short time. As a result, it was confirmed that the dynamic behavior such as runner vibration and pressure fluctuation under turbine operating range and the runner stress can be analyzed with the sufficient accuracy and due to applying as standard procedure in TOSHIBA, it can be avoided a failure risk in an early design phase. Moreover the fluid-structure interaction analysis method in this paper can be easily adapted to apply for other type of turbines, such as Francis turbines and Kaplan turbines.