The use of integrally bladed rotors, or blisks, in turbomachinery has been increasing due to improvements in performance and reduction in the number of components compared to traditional rotors. These components must withstand large centrifugal forces, as well as blade vibrations caused by upstream flow perturbations. The presence of flow forcing is particularly dangerous because the combination of a cyclic symmetric design of blisks and their inherent mistuning (i.e., small deviations from the nominal design) makes them prone to vibration localization. The lack of frictional interfaces in blisks results in lower structural damping, which in turn causes large vibration amplitudes. The presence of these effects combined with the large numbers of cycles that blisks blades must bear can lead to blade failure due to high cycle fatigue.

In the past, ring-like dampers have been employed to mitigate the low damping problem. However, the effectiveness that ring dampers provide is limited because they rely on the very small relative motion present between a damper and its groove. Other studies have proposed the use of impact or particle damping, which was found to be ineffective because centrifugal loads are so high that they cause the particles to be stuck.

This paper introduces a new type of damper, able to overcome the challenges that previous generations of dampers failed to solve. The major pitfalls of the damper concepts currently employed are two: the low level of relative motion that is available at the damper attachment location, and the inability to control the preload at the frictional interface. To address these issues, the proposed damper is designed as a tuned vibration absorber, which allows energy transfer from the blades to the damper provided that the natural frequency of the damper is close to that of the host structure. Thanks to the enhanced energy transfer, the damper can experience increased relative motion. Frictional contacts are then included to dissipate the energy transferred to the damper. The control of the contact preload is also important, as the centrifugal loads acting on the damper are extremely large and could result in the damper being stuck in its groove and not dissipating energy. These two requirements result in competing priorities. The damper structure must be stiff enough to withstand centrifugal loading without affecting the preload too much. However, it also must be compliant to make sure that its natural frequencies can match the ones of the host structure. For this reason, the proposed damper involves a complex geometry that is very stiff in the radial direction and softer in the circumferential direction, which is the direction of the relative motion. A model of the damper is created to dampen the vibration of a realistic blisk based on the NASA Rotor 67. The effectiveness of the damper is investigated using high fidelity finite element models. Due to the nonlinear nature of the contact, the equations of motion are solved using harmonic balance, and the size of the (linear part of the) system is reduced using Craig-Bampton component mode synthesis. The frequency response of the system is obtained to analyze the effectiveness of the proposed design. Preliminary results show the potential of this technology for structures with such low damping.


A Friction-Enhanced Tuned Ring Damper for Bladed Disks

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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