Analysis of First Stage Gas Turbine Blade for Evaluating Damping Energy and Failure Mode

Objectives: The turbine undergoes high temperatures, high stresses, and a potentially high vibration environment while in service. These vibrational stresses lead to fatigue failures. The percentage of failures gets reduced by dissipating vibratory energy. An alternate method that employed for reducing the high level of stresses within permissible limits is incorporation of damping. The objective of the paper is to evaluate total damping energy of real case of first stage gas turbine blade collected from the site. Methods/Analysis: The total damping energy of turbine blade is evaluated through Lazan's law. The CAD model of turbine blade is generated by using 3D scanner. The 3D data set of the scanned turbine blade is converted to a solid model. The modal and fatigue analysis of CAD model of turbine blade has been performed using ANSYS® software. The mass, volume, yield stress, resonant frequencies and total deformation at resonant frequencies are obtained through modal analysis. Equivalent alternating stresses is obtained from fatigue analysis. Findings: Equivalent alternating stress is used to calculate fatigue stress, which is further used with yield stress and volume to evaluate total damping energy of turbine blade. The total damping energy of the blade is used to evaluate loss factor and further equivalent damping co-efficient of turbine blade. From modal analysis results, it is found that there are stress concentration areas on leading and trailing edge of turbine blade at sixth resonant frequency. This shows that the turbine blade would be most susceptible to fatigue fracture at sixth resonant frequency. The available life cycle of blade is obtained from fatigue analysis. Application: The total damping energy of the blade is evaluated, which further used to calculate equivalent damping co-efficient of turbine blade. The failure mode and total available life of the turbine blade is predicted through computational analysis of turbine blade. This method is used as a necessary tool for the structural health monitoring of turbine blade in thermal power plants.