Many turbine blades are assembled on rotors with “under platform” dampers. These devices have two main effects: increase structural damping and modify the blade eigenfrequencies. During the design development of new turbine blades it can be useful to evaluate the damper effect in terms of eigenfrequencies with a simplified method incorporating OEM experiences.
In this paper a FE modal analysis of a turbine bladed disc assembly is described, incorporating the 3D CAD simplifications and FE model boundary conditions. The ANSYS program has been used for the simulation and the different configurations for this type of analysis have been investigated. Furthermore the “under platform” damper effects have been included in the post-processing of the analysis as a percentage contribution derived from technical literature. The calculated eigenfrequencies of the blade have been compared with experimental testing in an over-speed cell to validate the methodology. These experimental tests have been performed with strain gauges applied to blades. The complete stage row has been assembled in a particular balanced configuration with and without “under platform” dampers. The data capture allows the identification of the damper effect on the blade eigenfrequencies.
Finally the Campbell diagram with the different boundary conditions during the gas turbine start-up has been prepared. Comparing calculated eigenfrequencies with gas turbine excitation sources it is possible to evaluate the blade dynamic behavior and to study different design solutions if the component has insufficient separation with the engine order excitation.