Session: 28-02 Mistuning: Simulations & Experiments

Paper Number: 100665

100665 - Study on Identification of Modal Parameters of Mistuned Bladed Disks 

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 (the natural frequency, damping, etc.) of turbomachinery blades. When measuring the blade frequency, the blade damping, the vibratory stress, etc. by these methods, the rotor speed is gradually changed so as to pass through the resonance and the modal parameters are obtained by analyzing the measured frequency response. In measurement of the modal parameters of blades in rotation by these methods, it is pointed out that the mistuning of a bladed disk makes the identification of modal parameters difficult. Namely, because, for a mistuned bladed disk, responses of many vibration modes are excited and superposed, it becomes difficult to correctly identify the natural frequency and damping of an individual blade on a disk. 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 based on the reduced order model FMM (Fundamental Mistuning Model) is proposed, where the modal parameters of a mistuned bladed disk are identified using the frequency responses consisting of many vibration modes measured in the rotation test. For this purpose, the formulation of the FMM is modified so that the modal parameters and the excitation force (the engine order and the amplitude) become unknown variables and the frequency responses measured in the rotation test become input values. The derived equation is applied at each excitation frequency where the frequency response is measured and solved by the least square method to obtain the modal parameters and the excitation force. To verify the validity of the identification method proposed, typical mistuned systems of turbocharger and aeroengine 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, and an effective countermeasure for reducing the effect of measurement noise is also proposed. From these results, it is concluded that the modal parameters and the excitation force of a mistuned system can be identified with the practical accuracy applying the proposed method.

Presenting Author: Yasutomo Kaneko Ryukoku University

Presenting Author Biography: Graduated from the master course of Hokkaido University in March of 1981.
Joined Mitsubishi Heavy Industries, Ltd., in April of 1981.
He had worked in the field of the rotor dynamics for 30 years, especially in the filed of blade vibration, in Mitsubishi Heavy Industries, Ltd.
In April of 2009, he moved to Ryukoku University, and now, he works in the field of the rotor dynamics.

Authors:

Yasutomo Kaneko Ryukoku University
Toshio Watanabe Mitsubishi Heavy Industries, Ltd.
Tatsuya Furukawa Mitsubishi Heavy Industries, Ltd.