Eventos Anais de eventos
COBEM 2019
25th International Congress of Mechanical Engineering
A TEST-RIG FOR THE INVESTIGATIONS ON FRICTION DAMPERS USED IN TURBINE APPLICATIONS
Submission Author:
Marcelo Braga dos Santos , MG
Co-Authors:
Marcelo Braga dos Santos, Chiara Gastaldi, Muzio M. Gola, Tong Liu
Presenter: Marcelo Braga dos Santos
doi://10.26678/ABCM.COBEM2019.COB2019-2375
Abstract
Under-platform dampers are commonly adopted in order to mitigate the resonant vibration of turbine blades. The need for reliable models for the design of under-platform dampers has led to a considerable amount of technical literature on under-platform damper modeling in the last three decades.The devices considered by this paper are "solid" dampers (as opposed to flexible "sheet" dampers), small but relatively stiff metal components that, during service, are 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 problem to the designer is to have means to numerically simulate the damper mechanics, a task that can be fulfilled by a straightforward numerical model provided, however, that trusted values of contact parameters are available. Before the introduction of this test-rig, the traditional experimental configuration for evaluating under-platform damper behavior was, and still is, to measure the (non-linear) FRF of a blade after incorporating the damper between two adjacent blades representing a cyclic segment of the bladed disk. The effectiveness of the damper is then revealed by the difference in the blade response depending on the amount of radial force on the damper. It can be demonstrated, however, that parameter tuning is not unique, i.e., several combinations of contact parameters may produce the same response at a given mode. This does not produce contact parameters exportable to other modes or to other blades. The test-rig first designed and developed by the authors overcomes this problem by direct measurement of the forces applied from the damper to one of the platforms, and of the kinematics of the damper during the platform-to-platform hysteresis cycle. Over time, the method was refined by introducing additional "local" measurements of contact tangential cycles, and the determination of contact parameters has become increasingly reliable. The paper describes such improvements and illustrates how these are combined with a numerical twin of the damper so that, despite the complexity of the system, it is possible to obtain a clearer understanding of the friction damper behavior. This knowledge is transferred to the engineering applications where the amount of damping and frequency shift are important design factors.
Keywords
Turbine Blades, friction dampers, under platform dampers, friction measurements, mistuned blades
