Studies On Dynamics Of Aero-engine Rotor With Faults On Supporting Components

Supporting components are important parts of an aero-engine rotor system.The working state of the supporting components directly affects the reliability of the engine.Due to the complexity of working environment,supporting components are the most frequently fault-occurring parts in an aero-engine.Pedestal looseness fault and rolling bearing fault are the most common faults of supporting components.Both of the two types of fault have strong nonlinearities,which could lead to excessive engine vibration,rub-impact of rotor-to-stator,even cause serious damage accidents.Based on rotor dynamics theory,this paper carries out a research on rotor systems with pedestal looseness fault and rolling bearing fault respectively.The main work and achievements are as follows:1.A brief overview on the development of rotor the dynamics of the rotor with pedestal looseness faults and rolling bearing faults is given at the beginning of the thesis.The related theoretical knowledge is presented.2.For a rotor-bearing system with looseness between foundation and pedestal at one end,the Runge-Kutta numerical method is applied to calculate the dynamic response of the system.The result shows that the vibration waveform of the loose-end is asymmetric,with obvious clipping happens;Frequency spectrum have significant high frequencies.Under some specific speeds,the pedestal looseness can also cause vibration frequency spectrum component of the system with 1/2,1/3 frequencies.Through the experiment research some similar results are also obtained.3.Genetic algorithms are applied to identify the pedestal looseness fault parameters.In view of the traditional genetic algorithm having problems of slow evolution and premature convergence,an improved method based on the genetic process of the traditional genetic algorithm is proposed.Studies show that the improved method can effectively improve the efficiency of looseness parameter identification.The nonlinear parameters of pedestal looseness fault are identified by the improved genetic algorithm,and the influence of mutation rate on the identification results is studied.Finally,the looseness parameter identification based on the measured signals is performed with a satisfactory result.4.For an asymmetrical dual-disc rotor system,a dynamic model fully considered the VC(varying compliance)vibration arising from the periodic change of rolling bearings' stiffness is established by using Lagrange equation.The force models of the bearing with local damage on the outer or inner ring are established respectively.The method of numerical integration is applied to analysis the dynamic characteristics of the system with bearing fault on the outer or inner ring.It is shown that damage of the rings would have a great impact on dynamic characteristics of the rotor-bearing system.Especially in the low speed stage,the system's vibration amplitude increases with enlargement of the damage width.The damage on the outer ring will interfere with the effect of the bearing clearance's nonlinearity,while the damage on the inner ring will enhance the effect of this factor.The fault parameter identification of rotor-bearing system can provide a support to establish the model of real engineering problems,and it is of great significance in the field of fault monitoring and diagnosis.The achievement of the research on rolling bearing fault mechanism and the laws of bearing fault impacting on the movement characteristics of rotor system have a guiding significance to the diagnosis of bearing faults.