航空发动机双转子系统模态正交性和不平衡响应

Dual-rotor system has two sets of vibration modes excited by low-pressure rotor and high-pressure rotor, and the orthogonality of these two sets of modes is the core element of dynamic characteristics of dual-rotor system. Here, the dual-rotor dynamic model of aeroengine with intermediate bearing and bifurcation structure was established to analyze its modal orthogonality. The complex modal method was used to analyze modal orthogonality of dual-rotor system under different excitations, and the condition set of orthogonality was derived. It was shown that when the rotating speed ratio of dual-rotor system is constant, modes of dual-rotor system under their respective excitation ways are orthogonal with respect to stiffness matrix and inertia matrix; no orthogonality exists between modes under different excitation ways; based on modal orthogonality, after modal decomposition, the unified expression of unbalance response of dual-rotor system was obtained. Finally, a certain type aeroengine dual-rotor system was taken as an example to verify the above conclusions. The method combining discrete finite element and state vector was used to calculate modes under different excitations with constant or non-constant rotating speed ratio, and the modal orthogonality numerical value set was constructed to evaluate the orthogonality of modes. It was shown that the evaluation results are consistent with the derived orthogonality condition set.