RESEARCH ON MODES ORTHOGONALITY OF AERO-ENGINE TRI-ROTOR SYSTEM

This paper presents a dynamic model of aero-engine tri-rotor system included both common bifurcation structure and intermediate bearing for modes orthogonality analysis of tri-rotor system. The complex mode method is used to analyze the modes orthogonality of the tri-rotor system under different excitations and deduced the set of conditions for orthogonality. It is found that when the speed ratio of the tri-rotor system is constant and the damping matrix is the main symmetric matrix, the mode shapes of the tri-rotor system under the excitation of their respective frequencies are orthogonal, but there is no orthogonality between the modes from different excitations. Finally, a certain type of aero-engine tri-rotor system is selected as an example to verify the previous conclusion. The discrete finite element method 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. The evaluation results is agree well with the previous orthogonality condition set, and it is indicates the reliability of the proposed aero-engine tri-rotor system dynamic model.