Analysis of flow induced vibration of high head francis turbine

Abstract

The Francis hydro turbines are designed for the medium head power applications and in special circumstances, the high head Francis turbines are designed to convert the kinetic energy of the fluid to mechanical energy. The high head increases the potential of having high speed flow with high vibration levels. Hence, in high head Francis turbines design parameters should be optimized to get the maximum power output while avoiding abnormal phenomena such as excessive vibration, flow separation at the draft side, cavitation, and Karman vortex generation. Vane Pass Frequency (VPF) is one of the major issues that create series of harmful effects on the turbines and auxiliary parts because of superimposing of the vibration pulses and resonance of the adjacent parts. The VPF can resonate the auxiliary equipment, penstocks and turbines parts vibrate itself by forced vibration, which should be mitigated to protect the turbine. Hence, this research aims to study the flow induced vibration in high-head Francis turbines to establish the optimum parameters to mitigate the issues caused by vibrations. One of the power plants in Sri Lanka was used as a case-study for the research. At the final commissioning stage of this power station, a serious vibration and noise problem in the Francis turbine and steel penstock was detected. The dominant frequency of the vibration was identified as 180Hz and it was established that frequency generated from the turbine vanes. The study is continuing to analyse the remedial actions to minimize the vibration effects to the power plant equipment.