Condition Monitoring of Turbine Blades with Experimental Validation Using FFT Analyzer

Turbines in power industry uses pretwisted blades of varying lengths. And these blades are mounted on the rotating shafts with one end fitted in the fir-tree root of the rotor disk. The fatigue of these blades may cause crack to initiate at the stress concentration regions and may propagate for catastrophic failure. This paper addresses the condition monitoring of the turbine blades in the presence of crack using FFT analyzer. The influence of crack on the natural frequencies of turbine blade was investigated by conducting parametric studies using ANSYS software. It was observed that the natural frequencies of the cracked pretwisted blade are varying with angle of twist in all modes of vibration. Also, these natural frequencies were compared for long and short blades whose vibrational behavior was found to be dissimilar under the combined effect of pretwist and the presence of the crack.