Session: 28-05: Mistuning of bladed disks

Paper Number: 153549

Reduced-Order Modeling of Rotor Blades With Geometric Uncertainties 

The geometry of turbomachinery blades inevitably deviates from design specifications due to manufacturing processes or degradation during operation. These variations are often the major cause of mistuning, which is responsible for mode localization and high-amplitude response in resonance crossing.

Geometric uncertainties of blades have been represented through modal approaches, typically based on the Principal Component Analysis (PCA), leading to models in which the “as manufactured” geometry is specified by a limited number of parameters for each blade.

In principle, this information can be incorporated into a Finite Element (FE) model by reproducing the “as manufactured” geometry for each blade using mesh morphing or other procedures; however, two serious problems arise. First, this approach is not feasible for industrial-grade models of bladed disks as its computational complexity is very high. Second, this procedure may be used to simulate a specific bladed disk, constructed by a defined blade set, assembled with a specified order. On the other hand, it is unpractical if the interest is to explore several possible configurations to investigate the impact of random mistuning.

An alternative approach to investigate geometric uncertainties can be formulated by introducing the sensitivity of the mass and stiffness matrices with respect to the parameters used to represent the geometric variation of the blades. Assuming that the geometric variation is small, the dynamic properties of the disk may be obtained in the form of a series expansion whose coefficients can be computed relying only on the nominal geometry. Implementing this idea into a computational procedure requires: 1) to formulate a fast and reliable way to compute the sensitivity of the system matrices with respect to the geometric parameters; 2) to transfer this information into a Reduced Order Model (ROM) such a Subset of Nominal Modes (SNM); 3) to calculate the sensitivity of some relevant properties of the disk assembly such as natural frequencies, mode shapes and forced response amplitude.

The objective of this paper is to formulate the aforementioned procedure in such a way to be applied to an industrial-grade disk model.

Presenting Author: Luigi Carassale University of Genova

Presenting Author Biography: Full professor of Applied Mechanics at the University of Genova

Authors:

Abdelhakim Bouras University of Genova
Javier González-Monge Universidad Politécnica de Madrid
Luigi Carassale University of Genova