Study on identification of modal parameters of mistuned bladed disks

Abstract

To develop turbomachinery blades with high reliability, it is indispensable to verify the natural frequency, damping, resonant stress, etc. under operating condition, and utilize these data in the mechanical design of a new blade. BTT (Blade Tip Timing) and the telemetry system have been widely used to measure the modal parameters of turbomachinery blades. In measurement of the modal parameters of blades under rotation, it is pointed out that the mistuning phenomena make the identification of modal parameters difficult. Namely, because, in a mistuned bladed disk, responses of many vibration modes are superimposed, it becomes difficult to correctly identify the natural frequency and damping of an individual blade. This is one of the critical issues to be overcome for developing blades with high reliability. In this study, a novel identification method of modal parameters of a mistuned system is proposed, where the modal parameters of a mistuned bladed disk are identified using the frequency responses consisting of many vibration modes. To verify the validity of the identification method proposed, typical mistuned systems of a turbocharger are analyzed, and the modal parameters are identified. The effect of the noise included in the measured frequency response on the accuracy of the identification is examined in detail.