Nonlinear Dynamics On Impact-rub Of Aero Engine Rotor System

To increase the efficiency and thrust-weight ratio of aero engines, theclearance between rotor and stator has been designed to be smaller and smaller,however, which leads a larger possibility of impact-rub. Rubbing may induce therotor’s dynamic instability, blade break, and other serious accidents.In this thesis, rubbing dynamics of aero rotor system is investigated to givesome theoretical references for the design of aero engine. The main contents areas follows:SFARM (synchronous full annular rub motion) of a single-disc rotor withnonlinear stiffness is considered. The constraint bifurcation theory is firstlyapplied to discuss the influence of parameters on the jump phenomena at therotor’s run-up and run-down. The stability of SFARM is analyzed and the stableregion on the parameter plane is obtained. The possible dynamical behaviorsafter the Hopf bifurcation are also studied.Reverse full annular rub of nonlinear rotor system is studied analyticallyand numerically, which shows the necessity to consider the nonlinearity of rotorcompared with earlier test results. Analytical solution of reverse full annular rubis calculated and then its stability is discussed by Floquet theory. Influences ofparameters on the response and existence region, as well as the onset of reversefull annular rub are discussed. The results show that besides the dry frictionwhirl resulting from the change of direction of friction, another reverse fullannular rubbing motion caused by the rotor’s nonlinearity also exists. And thiskind of reverse full annular rub is a stable periodic motion. Transient andsteady-state responses of the sudden imbalance of the nonlinear rotors system areinvestigated. The transitions of steady-state response on the parameters-rotationspeed plane are given.Aero engine rotor system is simplified as an unsymmetrical-rigid-rotor withnonlinear-elastic-support based on its characteristics. Governing equations of therubbing system are solved by averaging method to obtain the bifurcationequations. Then bifurcation and stability of SFARM are analyzed according tothe two-dimensional constraint bifurcation theory and Lyapunov stability theory.Reverse full annular rub of the elastic-support rigid-rotor system is studied todiscuss the influences of parameters on the amplitude and frequency.The dynamical model of a dual rotor-casing coupled system is establishedconsidering the main characteristics of aero engine including dual rotor-intermediary bearing structure, nonlinear supports, gyroscopic effect, and hollow rotating shaft. The critical speeds and modes are solved and the influences ofsupport stiffness and rotating speed ratio are discussed. Rubbing response of thedual rotor-casing coupled system is calculated. The results show that jumpphenomena may happen for many times in light rubs. And co-rotating of the dualrotors may lead the combination of rotating frequencies, however,counter-rotating may not. Reverse full annular rub which is the same as the oneof single rotor system may happen in heavy rubs. The influence of massimbalance on the amplitude at the operating condition is discussed, which showsthe self-excited instability is easier to happen with the rotors’ counter-rotating.Sudden imbalance response of the dual rotor-casing coupled system is solved,and bifurcation diagrams of steady-state response with the variation of suddenimbalance are given. It shows that periodic motions, quasi-periodic motions andself-excited instability may appear in the co-rotating system, however, incounter-rotating system self-excited instability may not happen.