Optimization of the Contact Geometry Between Turbine Blades and Underplatform Dampers With Respect to Friction Damping

The blades of rotating compressor or turbine disks are subjected to fluctuating fluid forces that cause blade vibrations. To avoid high resonance stresses, in many applications additional damping is introduced into the bladed disk assembly by means of friction damping devices such as underplatform dampers. These are mounted between adjacent turbine blades and pressed onto the platforms due to centrifugal forces to dissipate energy by the generated friction forces due to relative motions between the damper and the neighboring blades. In real turbomachinery applications, the rotating blades are subjected to spatial vibrations caused by a complex blade geometry and distributed excitation forces acting on the airfoil. Therefore, a spatial model is presented including an appropriate spatial contact model to predict the generalized contact forces acting between the damper and the blades accurately. Six degrees of freedom are considered for each contact between the damper and the respective neighboring blades. Roughness effects are considered that determine the real contact area with respect to the nominal contact area. Different spatial blade vibration modes are investigated with regard to the friction damping that is provided by the underplatform damper. To gain the maximum damping effect, the damper mass is optimized at different working conditions of the assembly like the excitation amplitudes and the engine order. Furthermore, the influence of the contact geometry upon the damping potential is investigated in detail including the damper as well as the blade platform geometry. In practice, different damper geometries are in operation. Studies will be presented that prove the capability of the developed model to compare the effectiveness of different damper and blade platform geometries. Asymmetric platform angles leading to different contact conditions at the left and right damper contact, respectively, are studied in detail to improve the damping effect.