REDUCED ORDER MODELS FOR BLADED DISKS WITH CONTACT MISTUNING AT BLADE ROOT JOINTS

Mistuning occurring in bladed disks is a well-recognized problem in the turbomachinery industry, since it may significantly affect the dynamic behavior of the system by inducing localized amplification of the blade vibration when compared to the cyclically symmetric (tuned) configuration. Identifying the highest blade vibration amplitude requires the performance of a large number of simulations, which are usually run by introducing the mistuning in a Reduced Order Model (ROM), obtained from an initial very large Finite Element (FE) model. The traditional introduction of mistuning as blade frequency variation is being progressively replaced by methods that can correlate mistuning to a specific source (e.g.: geometric variations, changes in material properties, etc.). In this context, a novel reduction technique has been developed by the authors to take into account mistuning due to the contact uncertainties at the blade root joint, which can be caused by design tolerances, manufacturing processes, assembly procedures, and wear. The technique relies on the Craig-Bampton Component Mode Synthesis (CB-CMS) applied to the uncoupled blade and disk sector, which is usually included in most FE software. Afterward, the full set of master degrees of freedom is reduced using a suitable modal basis, according to the Gram-Schmidt Interface (GSI) method. The proposed reduction technique is firstly numerically validated in terms of modal parameters estimation and forced response computation. Afterward, the method is subjected to an experimental validation on a dummy bladed disk, which requires the previous estimation of the contact stiffness at the blade root-disk interface. Even if the contact stiffness parameter shows a limited influence on the system's linear behavior, the choice of a suitable value of this parameter is deemed to become relevant when the nonlinear behavior of contact interfaces is studied through penalty contact methods. The ultimate goal of the introduced technique is to obtain a good estimation of the maximum forced response of the bladed disk with a limited computational cost and with sufficient accuracy, provided by appropriate modeling of the mistuning at the blade-disk contact interface.