Under-Platform Damper Measurements at Politecnico di Torino

Abstract

In turbine bladed systems, some damping in addition to material damping is needed to attenuate forced vibration resonance amplitude and prevent high cycle fatigue of blades. Dry friction damping is recognized as an efficient way for the passive vibration control in the turbine industry. Under-platform dampers are widely used as a source of friction damping in turbo engines. The device considered by this chapter is a “solid” damper, as opposed to a “sheet” damper. It is a small but relatively stiff metal component that, during service, is loaded by centrifugal force against both platform undersides of two adjacent blades. When the relative movement between the blades increases such that slip between the damper and platform surfaces happens, blade vibration energy is dissipated through friction. The purpose of this chapter is to describe a method to develop calibrated models of under-platform dampers and to highlight the open problems. The results here presented were obtained from a particular type of cylindrical-flat damper, which is used in practice, slightly adapted to laboratory conditions. The results demonstrate that, despite the complexity of the system, it is possible to obtain a clear understanding of the damper behavior through its hysteresis shape. This finding is encouraging and paves the way to the development of a damper optimization process, which will be less a matter of trial and error and more a matter of deep insight into the damper dynamics.