In this paper, a method is proposed for the analysis of modal damping in mistuned bladed discs with root joints. The method is based on using of large finite element models and detailed description of contact interfaces of the joints and the effective approach for the mistuned bladed disc model reduction. The influence of mistuning on the distribution of dissipated energy for different blades on a bladed-disc and the modal damping factors for different vibration levels for any family of modes can be investigated.

The dissipated energy and the modal damping factors that are produced by friction under micro-slip motion at blade-disc root joints are assessed. The friction contact interaction is simulated by a large number of surface-to-surface friction contact elements using finite element software packages widely available. Due to the strongly nonlinear character of the contact interaction, the transient response analysis is performed until the steady-state vibrations are established. The three-dimensional finite element models of mistuned bladed discs are considered. In order to obtain the results in practically acceptable time of computations, an original reduction method is developed. The method allows the calculation of modal damping for the mistuned bladed disk by calculation of the dissipation energy at each blade of the bladed disk separately and considering in the transient analysis only a small part of the bladed disk sector.  

The method capabilities are explored by extensive studies of modal damping in a mistuned turbine bladed disk. The dependency of the modal damping factor on the analyzed bladed disk mode shape, engine-order excitation numbers, and the level of vibration amplitude are studied and the distributions of amplitude and dissipated energy on the mistuned bladed-disc are analyzed using a realistic mistuned blade disc model.


Analysis of Nonlinear Modal Damping due to Friction at Blade Roots in Mistuned Bladed Discs

Division / Sponsor:
International Gas Turbine Institute (IGTI)

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

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