Modeling and Identification of Mistuning in Bladed Disks
 

Structures that consist of a cyclic assembly of identical substructures are said to possess cyclic symmetry. The design of a single stage of a turbomachinery rotor, or bladed disk, typically features cyclic symmetry. Using cyclic symmetry routines in commercial finite element software enables one to analyze the entire bladed disk using a model of only one sector, which results in considerable reduction of computational costs. However, there are always small structural deviations among blades, called mistuning. Although mistuning is typically small (e.g., blade-alone natural frequency variations of 1-5%), it can lead to a dramatic increase in maximum blade stress and is a major driver for high cycle fatigue in turbine engines. From a modeling perspective, mistuning destroys the cyclic symmetry, such that the full bladed disk needs to be modeled. To address this issue, we develop efficient approaches for reduced-order modeling of mistuned bladed disks.

These reduced-order models treat mistuning as a variation in natural frequencies for one or more modes of an isolated blade. For bladed disks with inserted blades, one can measure the natural frequencies of manufactured blades directly. However, this is not possible with integrally bladed disks (blisks), which are becoming more prevalent in newer and next-generation engines. For blisks, we have developed several mistuning identification methods that use experimental response data for the full blisk in order to extract individual blade mistuning parameters. The combination of work on modeling and identification of mistuning in blisks in our research group has made it possible to accurately model blisks at a fraction of the computational cost compared to finite element analysis.

     
University of Michigan
College of Engineering