Analysis and Verification Test of Damping Characteristics of Steam Turbine Hollow Vane With Friction Damper

A vane used in a low pressure end of a steam turbine is usually fixed to a shroud and a casing by welding both ends. In such a vane structure, the damping in loading operation is comprised of the material damping and the aerodynamic damping, because the structural damping is very small. In the blade and vane of high-capacity steam turbine units, the aerodynamic damping may become negative under the high loading operation, and some papers reported the self-excited vibration of the blade and vane caused by the negative aerodynamic damping. Recently, in order to increase the reliability of the steam turbine vane, a hollow vane with a friction damper has been proposed. In such a steam turbine vane, the curved damper piece made of the thin plate is inserted into the hollow vane, and the structural damping is added by use of the friction between the damper piece and the vane. In this paper, for the purpose of clarifying the damping characteristics of the hollow vane with the friction damper, first, the excitation test of the model vane is carried out. In the excitation test of the model vane, the damping characteristics of the model vane consisting of two flat plates and the thin curved damper piece are measured, changing the excitation force. Second, the analysis method for predicting the damping characteristics of the hollow vane with the friction damper, which utilizes the conventional modal analysis method and the harmonic balance method, is proposed. The validity of the analysis method is verified by comparing the measured damping with the calculated ones. After verifying the analysis method, the actual steam turbine hollow vane with the friction damper is also analyzed, and the effect of the damper stiffness on the damping characteristics is examined. Finally, the actual hollow vane with the friction damper for the high-capacity steam turbine unit is designed and manufactured, and the excitation test of the actual hollow vane is carried out. From these results, the damping characteristics of the hollow vane with the friction damper are clarified.