Abstract
The finite element model of a dual-rotor system was established by Timoshenko beam element. The dual-rotor system is a coaxial rotor whose supporting structure is similar to that of an aero-engine rotor system. The inner rotor is supported by three bearings, which makes it a redundantly supported rotor. The outer rotor connects the inner rotor by an intershaft bearing. The spectrum characteristics of the dual-rotor system under unbalanced excitation and misalignment excitation were analysed in order to study the influence of coupling misalignment of the inner rotor on the spectral characteristics of the rotor system. The results indicate that the vibration caused by the misaligned coupling of the inner rotor will be transmitted to the outer rotor through the intershaft bearing. Multiple harmonic frequency components, mainly 1x and 2x, will be excited by the coupling misalignment. The amplitudes of all harmonic frequencies increase with the misalignment in both the inner and outer rotors. The vibration level of the outer rotor affected by the misalignment is lower than that of the inner rotor because it is far from the misaligned coupling. Harmonic resonance occurs when any harmonic frequencies of the misalignment response coincide with a natural frequency of the system. In order to verify the theoretical model, experiments are performed on a test rig. Both the experimental and simulation results are in good accordance with each other.
Highlights
Rotor misalignment is one of the most common difficulties in the operation of rotating machinery
Feb is the external force of bearings. e difference between the ordinary bearing and intershaft bearing is that the external force on the intershaft bearing should include the interaction forces between the two nodes connected by the intershaft bearing. e interaction forces, Fintershaft and –Fintershaft, are shown in Figure 4. e intershaft bearing connects node j of the outer rotor and node i of the inner rotor. e inner and outer rotors interact with each other through the intershaft bearing. e interaction forces
Because the inner rotor is supported by three bearings, the supporting structure can only be an angular misalignment
Summary
Rotor misalignment is one of the most common difficulties in the operation of rotating machinery. Lu et al [36] presented a theoretical research on the nonlinear response characteristics of an aero-engine dual-rotor-bearing system with flexible coupling misalignment faults in the inner rotor. Li et al [40] investigated the quantification of uncertainty effects on the dynamic responses and vibration characteristics of a multirotor bearing system with the fault of angular misalignment. Ren et al [41] presented a dynamic model of a flexible rotor system with multisupport in order to solve the bearing misalignment problem of the rotor system in an aero-engine. Erefore, the spectrum analysis of an aero-engine multibearing dual-rotor system with coupling misalignment and disk unbalance has been studied by the finite element method (FEM) in the present study. E study could be useful in the detection of misalignment in the coaxial dual-rotor system diagnosis and in the design of an aero-engine rotor system Experiments were performed on the test rig under different intentional misalignment conditions. e study could be useful in the detection of misalignment in the coaxial dual-rotor system diagnosis and in the design of an aero-engine rotor system
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