Testing, Simulating and Understanding Underplatform Damper Dynamics

Underplatform dampers (UPDs) are widely used as a source of friction damping and are frequently incorporated into compressors and turbines for both aircraft and powerplant applications to mitigate the effects of resonant vibrations on fatigue failure. The need for reliable models of UPDs has led to a considerable amount of literature in the last three decades. The standard approach is to fine-tune and experimentally validate the UPDs models by comparing measured and calculated vibration response of blade pairs. With this approach one cannot investigate the damper behaviour directly and no measurements of the contact parameters can be undertaken. The experimental-numerical method proposed by these authors overcomes this problem through the combined use of purposely developed tools: - a test rig capable of measuring directly the damper working parameters (i.e. damper hysteresis cycle and kinematics); - error estimates of measured and derived forces and displacements ; - a numerical routine representing the damper between the platforms solved either in the time or in the frequency domain; - a robust procedure for the estimation of friction and stiffness parameters at the contact from experimental data. These tools combined together offer concrete prospects of success in damper simulation and design. On one hand, they allow mapping the values of contact parameters under different working conditions (i.e. frequency, centrifugal load and presence/absence of damper rolling), thus ensuring valuable predictions both at the design and at the simulation stage. On the other hand the experimental-numerical method offers a clear understanding of all contact events (stick, slip, lift) which take place during the cycle, and on how they influence the damping performance. This deeper insight is the basis to actual design and optimization criteria. Purpose of the paper is to illustrate the tools and methods through the analysis of a family of rigid bar dampers with a curved-flat cross section. A series of diagrams fit to describe the damper behaviour will be presented and used to estimate relevant friction contact parameters.