Friction damping devices such as under platform dampers are installed for modern turbine blades to suppress dynamic vibrations of the blades. In order to secure the reliability of the blades, it is important to predict the dynamic response and friction damping characteristics accurately. In this present paper, the dynamic response and friction damping characteristics of a last stage blade (LSB) of a steam turbine with contact surfaces at the cover, tie-boss and blade root was investigated. Especially, it is focused on the effect of the non-uniform normal contact forces at the contact surface. To investigate the effect of non-uniform normal contact forces, an analysis method was developed. Analysis model of the LSB with contact surfaces was discretized by finite elements. Tangential forces at the contact surfaces were modeled by multi-DOF macro-slip modeling. The non-linear frequency responses of the LSB were obtained by using the harmonic balance method. Using this analysis method, the relationship between the contact surface behavior and the dynamic response was studied.

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