Vibrational responses and fatigue life of dynamic blades for compressor in gas turbines

Abstract

The installing angle of the static blades of the compressor in gas turbines affects the aerodynamic forces which leads to the vibration variation of the dynamic blades, and may causes the High Cyclic Fatigue failure of the blades. In order to study the influence mechanism of the installing angle on the fatigue life of the blades, the finite element model of the cyclic symmetrical impeller structure is established, and the aerodynamic loads under the various configurations are exerted to the surface of the blade. The modal analyses under the airflow prestress and the centrifugal force are carried out and the main natural frequencies are obtained. In order to verify correctness of the finite element modeling method, the harmonic response analysis is also conducted. The transient dynamic method is adopted to solve the vibrational responses of the blade under consideration of the Rayleigh damping. The displacement responses of the key points on the blade are calculated and are compared with the experimental results to select the reasonable damping for the life analysis. Applying Goodman and S-N curves, the fatigue life of the blade is analyzed to assess the safety of the structures. By comparison of the vibrational displacement of the experiment and the numerical calculation, the reasonable damping value is determined for the vibration response and fatigue life calculation. The fatigue life calculations of the two configurations are carried out under the premise of the approximate same mean values of the dynamic stress, the influence of the amplitude of the dynamic forces on the fatigue life is very significant. The amplitude and mean value of the dynamic stress at the danger points of the blade root should be paid more attention.