Abstract
In order to control the risk of high cycle fatigue of bladed disks, it is important to predict precisely the vibration levels and to design damping solutions to attenuate them. Therefore, Snecma has made some efforts in the last years in order to characterize better the damping in aero-engines. Among the various damping sources, friction damping is particularly difficult to model due to its non-linear behaviour [1]. For that purpose, two methods based on multi-harmonic balance strategy have been especially developed for Snecma, dedicated to the study of the non-linear forced response of bladed disks. The first one enables to model the bladed disk equipped with dry-friction dampers [2], and the second one takes into account intrinsic friction located in disk-blade interface [3]. To validate both models experimentally, a test campaign has been carried out in a vacuum chamber on a rotating bladed disk excited by piezoelectric actuators. The blade shanks have been softened in order to increase friction effects. Experimental results show a regular and reproducible behaviour of the non-linear forced response, over various rotation speed and excitation levels. The contributions of friction dampers and friction in blade attachment have been decoupled thanks to glue applied in the blade root. Both friction phenomena that were observed experimentally at resonance of the blade first bending mode have been reproduced numerically. After updating modeling parameters, an acceptable correlation was found on resonance frequencies, amplitudes and damping levels over the full experimental setup range, which validates these numerical tools for their use in design process.
Highlights
The mechanical design of aero-engines bladed disks requires numerical tools to predict the stability and forced response of the blades under aerodynamic loads
This paper deals with 2 kinds of friction damping phenomena in bladed disks : 1) due to contact in blade-disk attachments, 2) due to friction dampers placed between adjacent blades for vibration attenuation
Snecma has integrated in its design process two numerical tools based on HBM: 1) a first tool based on Dynamic Lagrangian Frequency Time method (DLFT) [9], and 2) a second tool based on single- and multiple-point friction dampers models [7]
Summary
The mechanical design of aero-engines bladed disks requires numerical tools to predict the stability and forced response of the blades under aerodynamic loads. It is important for an aero-engine designer to evaluate precisely the static and dynamic behaviour of the structure, the aerodynamic loads [4] and the various damping sources (material, aerodynamic and friction). The comparison between numerical and experimental results is a hard task, due to the non-linearity of friction phenomena and problems of repeatability [9], [10].
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