Monitoring and experimental validation of blade vibration forces acting on rotor

Monitoring of blade vibration is an important part in the maintenance of the rotating machine and its proper operation. The signal analysis of blade vibration plays an important role in detection of the blade structure change. Early detection can avoid unnecessary losses. This is important especially for blades in last stages of low-pressure turbine of turbo-generators. The popular method used for blade vibration monitoring is blade tip timing, which is, unfortunately, not installed standardly yet due to the higher installation costs and needs for adjustment of the stator part. However, when there is no blade vibration monitoring system installed on the turbine, there is a possibility to use an alternative method for blade vibration monitoring based on the analysis of the shaft relative vibration. In this case, the signal is measured by standardly installed instrumentation giving this method a major advantage upon the others. Recently, there was published a few papers describing this approach. However, there is no exact explanation yet how blade vibrations affect the shaft vibration and what is the form of its transmission. Explanation of main principle of rotor excitation by rotating blades, specifically description of forces taking part in the blade-shaft vibrations transfer are described in this paper. Experimental validation using a machinery fault simulator and derived conclusions are presented as well