Failure investigation of a Francis turbine under the cavitation conditions

Abstract

Acoustic-Structural coupling methodology has been used to numerically investigate the failure of a Francis turbine runner that broke down within one day of operation. The goal of the work has been to determine the feasibility of a resonance condition under cavitating flow conditions. The obtained results prove that the presence of large vapor cavities increase the natural frequencies of the diametrical modes of vibration in comparison with the pure water condition. In particular, a possible tuning between the hydrodynamic excitation and the 4ND mode has been found.