Abstract
Nonlinear dynamic model of a coaxial rotor system was established with a method combining the finite element method and the fixed interface modal synthesis method. Then an implicit time domain method was presented to solve the nonlinear equations of motion; thus dynamic characteristics of the rotor system can be obtained. With nonlinear forces of squeeze film damper and intermediate bearing considered, nonlinear dynamic response characteristics of the co- and counterrotating coaxial rotor system under multiple unbalance forces were studied and compared in this work. It was found that the critical speeds of the corotating system were equal to or slightly higher than those of the counterrotating case due to the gyroscopic moments. The results showed that the unbalance excitation frequencies are dominant in the responses of the rotor system. Besides, due to coupling effect of the intermediate bearing some combinations of the unbalance excitation frequencies were also observed in the spectrogram but the combinations were different for co- and counterrotating cases. Stability and periodicity of the rotor system were investigated with bifurcation diagram, Poincare map, and phase diagram. It was found that the rotor system executes four-period quasi-periodic motion around critical speeds.
Highlights
In recent years, coaxial dual-rotor system has been applied to many aeroengines with two corotating or counterrotating rotors, such as RB211, GE120, and F119
The current study is on a co- and counterrotating dualrotor test rig that has been developed to study the dynamics of dual-rotor machines with intermediate bearings and squeeze film dampers
The purpose of this paper is to study the modeling method and nonlinear dynamic characteristics of the complex dual-rotor systems
Summary
Coaxial dual-rotor system has been applied to many aeroengines with two corotating or counterrotating rotors, such as RB211, GE120, and F119. The squeeze film dampers (SFD) are commonly adopted to provide structural isolation and reduce the amplitude of rotor response All these facts necessitate that more studies should be conducted to investigate the dynamic characteristics of dual-rotor systems with SFD and the intermediate bearing. The finite element method has been applied in [10, 11] to obtain the dynamic characteristics of dual-rotor system with intermediate bearing. The current study is on a co- and counterrotating dualrotor test rig that has been developed to study the dynamics of dual-rotor machines with intermediate bearings and squeeze film dampers. Nonlinear dynamic characteristics of the co- and counterrotating test rig are studied and the numerical results are compared with the experimental results to validate the model established in this paper
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