Influence of Geometric Design Parameters Onto Vibratory Response and HCF Safety for Turbine Blades With Friction Damper

Among the major concerns for high aspect-ratio turbine blades are forced and self-excited (flutter) vibrations which can cause failure by high-cycle fatigue. The introduction of friction damping in turbine blades, such as by coupling of adjacent blades via under platform dampers, can lead to a significant reduction of resonance amplitudes at critical operational conditions. In this paper, the influence of basic geometric blade design parameters onto the damped system response will be investigated to link design parameters with functional parameters like damper normal load, frequently used in nonlinear dynamic analysis. The shape of a simplified large aspect-ratio turbine blade is parameterized along with the under platform damper configuration. The airfoil is explicitly included into the parameterization in order to account for changes in blade mode shapes. For evaluation of the damped system response under a typical excitation, a reduced order model for non-linear friction damping is included into an automated 3D FEA tool-chain. Based on a design of experiments approach, the design space will be sampled and a surrogate model is trained on the received dataset. Subsequently, the mean and interaction effects of the true geometric blade design parameters onto the resonance amplitude and safety against high-cycle fatigue will be outlined for a critical first bending type vibrational motion. Design parameters were mainly found to influence the resonance amplitude by their effect onto the tip-to-platform deflection ratio. The HCF safety was affected by those design parameters with large sensitivity onto static and resonant vibratory stress levels. Applying an evolutionary optimization algorithm, it is shown that the optimum blade design with respect to minimum vibratory response at a particular node can differ significantly from a blade designed toward maximum HCF safety.