Modal Based Sensitivity Analysis of Crack in Turbine Blades Using Validated Finite Element Models

Abstract

Turbines in power industry use pretwisted blades of varying lengths, which are mounted on the rotating shafts with one end fitted in the fir tree root of the rotor. The fatigue of these blades may cause crack that starts at the stress concentration regions and may propagate for catastrophic failure. This paper addresses the vibration behavior of the pretwisted blades under the influence of crack. The effect of crack on the natural frequencies of pretwisted blade is investigated by conducting parametric studies using finite element analysis software. The results obtained are used to evaluate the influence of crack on turbine blade after validating with experimental results. It has been observed that the crack in a blade had a considerable effect on the natural frequencies that change with varying pretwist angles in all the modes of vibration. In addition, the crack sensitivity for natural frequencies of long and short blades has been compared and the fatigue behavior of these blades has been analysed.