Dynamic Characteristics Optimization Of A Four-support Dual-rotor System With Intermediate Bearing

Supporting schemes for a variety of domestic and foreign military aero-engines were comparedand analyzed, and dynamic characteristics of a four-support dual-rotor system with intermediatebearing were analyzed and optimized in this paper. The conclusions are listed as follows:(1) Dynamic characteristics of the dual-rotor system with intermediate bearing were analyzedwith mode synthesis method and transfer matrix method. It was found that the inner rotor behaved inbend mode and the outer rotor in rigid mode at the first order critical speed excited by the inner rotor.Besides, vibration mode of the second order critical speed excited by the outer rotor was a littledifferent, large displacement emerged at the last support of the outer rotor, the inner rotor bended alittle. In addition, the value of the first two orders critical speeds were comparatively low and easy tosurpass them.(2) The critical speeds of the dual-rotor system were optimized by adjustments of the supportstiffness. The sensitivities of the objective function and the critical speeds on support stiffness werecalculated at working speeds and the critical speeds of dual-rotor system were optimized by changingthe support stiffness so as to avoid the forbidden frequency zones. The results for optimizationshowed that the critical speeds can be optimized effectively by the sensitivities as guidance. Theanticipated target can be achieved with only two elastic supports, which was of great benefit to reduceweight and unit design for the actual aero-engines.(3) The results of research showed that the support damping had different sensitivities to theunbalance response of the rotor system according to unbalance response optimization of the criticalspeed. The sensitivity analysis can effectively guide support damping adjustment and providedirectional guidance for the unbalance response optimization. The damping of support No.4did notaffect the unbalance response markedly by comparing the curve of objective function-damping aboutsupport No.1and No.4wherever it changed a lot, while damping of support No.1didn’t have thecharacteristic. So the damping of support No.1must be very careful to be chosen, while the dampingof support No.4more loose.