Parametric study of the kinematic behaviour of the underplatform damper and correlation with experimental data

摘要

High cycle fatigue is one of the main causes of failure of bladed discs. Blades of turbine are loaded by centrifugal force as well as variable amplitude force due to fluctuating flow following in blade vibrations. Underplatform Dampers (UPD) are commonly used to dissipate energy of vibration and reduce resonant amplitudes in bladed discs. UPDs are pieces of metal loaded by the centrifugal force and pressed against the platforms of two adjacent blades. Energy is dissipated by friction. To predict the forced response of the blades with UPDs information are needed about i) the friction coefficient, ii) the contact stiffness and iii) the static normal pre-load N{sub}0. The contact forces acting on the UPD are computed by damper balance equations. The contact model allows simulating three different states: stick, slip and separation. When the contact is fully stuck, the static value of the static normal pre-load is non-unique. As a result, a range of variability in the forced response of the system is numerically predicted. An extensive test campaign, with UPDs of different geometry and various centrifugal and excitation forces, has been performed. The experimental data are scattered between an upper and a lower limits. The experimental data are compared with the numerical simulation and, for the first time, the experiment data scattering is explained as a consequence of the non-uniqueness of the static normal pre-loads.