Fluid structure interaction of Francis-99 turbine and experimental validation

Abstract

The ability to predict a francis runners dynamic response to the exciting forces is paramount to avoid unwanted disintegration of the turbines components. In this article, each of the principal factors contributing to the dynamic response of the runner; eigenfrequency, mode shape, damping and pressure force, is individually examined and compared to the measured values from the Francis-99 runner. Even though the runner is made with a bolted connection between the blades and crown/band, and thus severely increasing the complexity, quite accurate predictions are possible using methods previously validated for massive and symmetric runners. All calculations are conducted on the best efficiency point and with eigenmodes corresponding to Nodal Diameter 4 as excited by the second harmonic of the guide vane passing frequency. The calculated natural frequency for the first two ND4 eigenmodes are within ±5% of the measured values. Further are the calculated eigenmodes, forcing pressure field and hydrodynamic damping all within measurement tolerances with some minor exceptions.