Nonlinear Dynamic Response Analysis Of Dual-rotor System

Dual-rotor aero-engine has been widely used owing to its competitive superiorities, the problems, however, it produces are increasingly complex, the deeper research on dynamic characteristics of dual-rotor system is highly required as well as meaningful. This paper studied a dual-rotor system which has intermediary bearing, the main contents as follow:⑴ A dual-rotor model with roller bearing as the intermediary bearing was built and then motion functions of this system were derived by rotor dynamics and Langrange equations. Hysteresis was found in this system by numerical calculation, and the influences of speed ratio, intermediary bearing’s radial clearance, damping ratio, the number of rollers, rotor ’s unbalance and direction difference between high pressure and low pressure rotor to hysteresis were studied respectively. It turned out that the increasing of speed ratio’s absolute value grows a larger jump range while a narrower hysteresis region, and hysteresis moves left, the critical speed of rotation turns down. The larger the intermediary bearing’s radial, the wider the hysteresis region, but the jump amplitude almost unchanged. Hysteresis region and jump amplitude would decrease due to the larger damping ratio which also makes the hysteresis region move left and turns down the critical speed of rotation. With the increasing of roller numbers, hysteresis region and jump amplitude would highly decrease, simultaneously, hysteresis region moves left as well as the critical speed of rotation decreased. When there is a larger unbalance, hysteresis region would move left with the same large while jump amplitude and critical speed of rotation increasing. Co-rotating and counter-rotating almost have the same performance in hysteresis. ⑵ By using the different displacement function, motion equations of the new dual-rotor system were derived, and then the influences of speed, speed ratio, damping and rotor unbalance to nonlinear responses of the system were studied. Results indicated that both of high pressure rotor and low pressure rotor showed almost the same characteristics under different speed. Besides, the motion of system is periodic when rotation speed is in the vicinity of the critical speed of rotation excited by high pressure rotor or low pressure rotor. Lastly, increasing speed ratio or damping, decreasing rotor unbalance would help weaken the nonlinear vibration of system and make the motion of system periodic.⑶ The surface waviness on both of inner raceway and outer raceway of intermediary bearing were considered when built the dual-rotor system, and then motion equations were derived by rotor dynamics and Langrange equations. The influences of speed, waviness amplitude, waviness order and the initial amplitude of waviness to nonlinear responses of system were studied. Results showed that the surface waviness effects almost the same on both of high pressure rotor and low pressure rotor. With the increasing of speed, both of high pressure rotor and low pressure rotor show a alternative variation of periodic motion and non-periodic motion. Besides, the influence brought by surface waviness is distinct when system is in low and medium speed. By decreasing the amplitude of surface waviness, the running of dual-rotor would turn to stable. The motion would might be non-periodic when waviness order is integer multiples of the number of rollers. A larger initial amplitude of surface waviness would help weaken the influence, which comes from surface waviness, to vibration amplitude of system.