Robust modeling of the nonlinear dynamic mistuning of bladed disks. – TURBODYNA

This project concerns the robust prediction of the mistuning of bladed-disks in nonlinear dynamics. The ideal situation, which consists in using the cyclic symmetry property of such structures and in analyzing the dynamical linearized response, yields biased estimates, which underestimate the real response levels. The blade mistuning concept is then introduced because the blades of a bladed disk are slightly different from one to another one. Such mistuning is induced by the dispersion in the materials, by the geometry (manufacturing tolerances), and by the boundary conditions and the blades-disk interfaces and is not without consequence when analyzing the forced response of the bladed disk. From the modal analysis point of view, the mistuning effects are characterized by a high modal density of modes which are spatially localized on the blades. From the forced response point of view, it is observed that the vibratory energy of a mistuned bladed disk is localized on few blades and causes large response levels with respect to the ideal situation of cyclic symmetry. Current advances in aircraft design of turbomachinery use blisks for engines and turbines for which the response levels belong to a nonlinear vibration domain. For this reason, it is no longer possible to use linearized theories in the modelling.
The quest for higher performance, combined with the economic challenges of crisis, led to bold technological choices, for which the blisks have a limited number of sectors and are made up of lighter materials. The two main drawbacks are (1) that the fewer blades, the more stressed blades and (2) that the damping of these structures is particularly weak compared to usual bladed-disks. Consequently, the bad effects related to the mistuning are amplified, and large vibration amplitudes can be commonly observed. Thus, it is no longer possible to use linearized theories. The project consists in constructing predictive models of mistuned blisks in nonlinear dynamics. There are three objectives in this project, consisting in: (1) developing an adapted methodology for the robust prediction of the nonlinear response amplification induced by the mistuning, (2) building advanced simulation tools, (3) validating and developing all of these new tools in an industrial context.