Detection of Cracks in Mistuned Bladed Disks Using Reduced Order Models and Vibration Data

Abstract

A novel methodology to detect the presence of a crack and to predict the nonlinear forced response of mistuned turbine engine rotors with a cracked blade and mistuning is developed. The combined effects of the crack and mistuning are modeled. First, a hybrid-interface method based on component mode synthesis is employed to develop reduced order models (ROMs) of the tuned system with a cracked blade. Constraint modes are added to model the displacements due to the intermittent contact between the crack surfaces. The degrees of freedom (DOFs) on the crack surfaces are retained as active DOFs so that the physical forces due to the contact/interaction (in the three-dimensional space) can be accurately modeled. Next, the presence of mistuning in the tuned system with a cracked blade is modeled. Component mode mistuning is used to account for mistuning present in the un-cracked blades while the cracked blade is considered as a reference (with no mistuning). Next, the resulting (reducedorder) nonlinear equations of motion are solved by applying an alternating frequency/time-domain method. Using these efficient ROMs in a forced response analysis, it is found that the new modeling approach provides significant computational cost savings, while ensuring good accuracy relative to full-order finite element analyses. Furthermore, the effects of the cracked blade on the mistuned system are investigated, and used to detect statistically the presence of a crack and to identify which blade of a full bladed disk is cracked. In particular, it is shown that cracks can be distinguished from mistuning.

Vibratory characteristic analysis of integral mistuned bladed disk assemblies for aeroengine

“…[6][7][8] It includes the free interface substructural CMS, the fixed interface substructural CMS, and the hybrid interface substructural CMS. 1,5,7,9 The basic idea is a kind of 'pieces' analytical method.…”

Numerical Study on the Dynamic Behavior of a Francis Turbine Runner Model with a Crack

“…Though it seems the geometries of the band and crown are very different from the disk of the traditional bladed-disk structures, from the theoretical viewpoint, there are no essential differences between them. For bladed-disk structures with crack, the well-known vibration localization can occur, which has been used for crack monitoring in many other types of turbines [9][10][11][12]. The vibration localization in Francis turbine has been studied very limitedly in the literature.…”

“…Generally, for traditional bladed-disk structures the crack has a more significant influence on blades dominated modes due to the lower coupling stiffness and causes some modes quickly localized to the damaged blade. This is the reason why most of researches focus on blade-dominated modes [9][10][11][12]. For the strongly localized mode, the frequency quickly deviates from the original tuned frequency.…”

“…For the strongly localized mode, the frequency quickly deviates from the original tuned frequency. Therefore, this natural frequency deviations and forced response changes of the runner may be detected by the monitoring system, which is the mechanical basis used for crack monitoring [9][10][11][12].…”

Automated Experimental Modal Analysis of Bladed Wheels with an Anthropomorphic Robotic Station

“…Due to the component cyclic symmetry, only one sector could be modelled in order to reduce the number of elements, however, neglecting any mistuning. Several methods can be exploited to take into account mistuning within a FE analysis [11,[33][34][35] but some experimental data are needed to calibrate these models. The experimental results confirmed that for the bladed wheels tested, mistuning slightly affects a few natural modes, above all introducing a separation between double modes.…”