Modal orthogonality and unbalance response of aeroengine dual-rotor system
HUANG Jiangbo1, LIAO Mingfu1, CHENG Ronghui2, GU Yuanxing3, LI Ming3
1.School of Power and Energy, Northwestern Polytechnical University, Xi’an 710072, China；
2.Shenyang Engine Design and Research Institute, Aero Engine Corporation of China, Shenyang 110015, China；
3.China Gas Turbine Establishment, Aero Engine Corporation of China, Chengdu 610500, China
Abstract：A dual rotor system possesses two sets of modes respectively subjected to low pressure rotor excitation (LRE) and high pressure rotor excitation (HRE). The orthogonality of these modes should be ascertained to modify the dynamics of dual rotor systems. Therefore, this paper presents a dynamic model of aero-engine dual-rotor system included both common bifurcation structure and intermediate bearing for modes orthogonality analysis of dual-rotor system. The complex mode method is used to analyze the modes orthogonality of the dual-rotor system under different excitations and deduced the set of conditions for orthogonality. It is found that when the speed ratio of the dual-rotor system is constant, the mode shapes of the dual-rotor system under the excitation of their respective frequencies are orthogonal, but there is no orthogonality between the modes from different excitations. In addition, through modal decomposition based on modes orthogonality, a unified expression for the unbalanced response of the dual-rotor system is obtained. Finally, a certain type of aero-engine dual-rotor system is selected as an example to verify the previous conclusion. The combined method of discrete finite element and state vector is used to calculate the modes under different excitations when the speed ratio is constant or not, and the modes confidence function is used to evaluate the orthogonality of the calculated modes, and the mode orthogonality numerical is constructed to evaluate mode orthogonality. The evaluation results are consistent with the deduced orthogonality condition set.
Key words: orthogonality of modes; response to unbalance; aircraft engine; dual rotor; speed ratio
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