Reflection On Dynamical Behavior Of Rotor With Bearing Clearance-fitted

Among all those involved in aero-engine structure design,bearing assembly process and fit tolerance are key points.In the context of the bearing assy in the hot end,this project pays special attention to bearing outering with clearance fit and bearing innerring with clearance fit respectively,which investigates the rotordynamic behavior of the aero-engine dynamical response theoretically,numerically and experimentally.The 1d clearance-collision-friction model,horizontally assembled bias-disked rotor model having bearing outer ring with clearance fit,vertically assembled bias-disked rotor model having bearing outerring with clearance fit,horizontally assembled bias-disked rotor model having bearing innerring with clearance fit and vertically assembled symmetrcial-disked rotor model having bearing innerring with clearance fit are respectively formulated in ordinary differential equation(s)which characterize the rotor-bearing system under the influence of nonlinear factors,say clearance,collision and friction,etc.These ordinary differential equation(s)are solved by numerical integration accordingly.The dynamical response of the rotor-bearing system against various values of factors including clearance,the maximum static friction,stiffness of the support,unbalance and friction model is exploit,which presents a series of nonlinear phnonmena.The 1d clearance-collision-friction model demonstrates nonlinear resonance at super-critical speed where the rotor-bearing system to excitation at about an whole number multiple(n)of its nature frequency,responces at vibrating asynchronously at its natural frequency,that is,at(1/n)of the excitation;vertically assembled bias-disked rotor model having bearing outerring with clearance fit demonstrates nonlinear resonance and combination resonance if the friction applied on the bearing outer ring faces is neglected;horizontally assembled bias-disked rotor model having bearing outer ring with clearance fit demonstrates sub-harmonic vibration,super-harmonic vibration,so called “all frequency” vibration and local resonance,etc.Similar nonlinear phenomena occur to horizontally assembled bias-disked rotor model having bearing innerring with clearance fit as well;the so called “all frequency” vibration is resulted from Stick-Slip instead of Coloumb friction model.A more tightly fitted outerring(innerring)as well as a larger outerring(innerring)locking torque evidently attenuates the nonlinear vibration.Vertically assembled symmetrcial-disked rotor model having bearing innerring with clearance fit is reported to experience instability due to interior friction.Experimental data from Muszynsk,etc,are referenced to verify the 1d clearance-collision-friction model by showing that a rotor according with the very model experiences nonlinear resonance at super-critical speed;experimental data from Ishida,etc,are referenced to verify the vertically assembled bias-disked rotor model having bearing outerring with clearance fit by showing the nonlinear resonance and combination resonance emerge from the rotor according with the very model,which is free from the friction force applied on the bearing outerring faces.All the referenced experimental data compare favourably with those found numerically.A test rig of horizontally assembled bias-disked rotor is employed to the study of the dynamical response of the rotor-bearing system under the influnce of various values of bearing outerring fit tolerence and bearing outerring locking torque.Phenomena including super-harmonic vibration,sub-harmonic vibration,“all frequency” vibration and local resonation,etc are indentified experimentally.A tighter bearing outerring fit well restricts the nonlinear vibration,whereas larger locking torques make no difference to that.The bearing innerring with clearance fit results in the similar vibration.Clearance,collision,and friction lead to nonlinear vibration,say nonlinear resonance,combination resonance,super-harmaonic vibration,sub-harmonic vibration,and local resonace,etc,which introduce extra resonant speeds to the rotor-bearing system,make the rotor subject to low and high circle of fatigue,and intensify the components' vibration.In conlusion,for aero-engine bearing,there is supposed to be no clearance between the outerring and the bearing house and between the innerring and the shaft at the operational condition,which is developed as the fundamental rule for aero-engine bearing assembly technology.