| In order to satisfy the requirements of processing,transportation,maintenance and performance,the rotor system of heavy-duty gas turbines more and more uses the disc-type rod fastening rotor in the design and manufacture process to replace the traditional integral rotor.The rod bolts are used to press the discs form the rotor.Unlike the integral rotor,the contact between the rough surfaces of the discs will cause the rigidity of the rod fastening rotor to change,which will affect the dynamic characteristics of the system,and it will also make it difficult to establish the rotor dynamic model.In this work,the rod fastening rotor system is taken as the research object.The dynamic model of the rod fastening rotor-bearing system considering the disc contact is established,and the dynamic characteristics of the rotor system under disc contact,unbalanced faults,structural asymmetry and misalignment faults are analyzed by simulation.The main research contents and results are as follows:(1)The rod fastening rotor system considering the contact between the joint surfaces of discs is taken as the research object.Based on the fractal theory,the normal contact stiffness expression considering the frequency index of the asperities is derived.The influence of frequency index,fractal dimension and characteristic length scale on normal contact stiffness are discussed by numerical analysis.It is calculated that the minimum frequency index determines the volume of the asperities.The smaller the value,the larger the volume of the asperity.The fractal dimension determines the morphology of the rough surface.The larger the value is,the more the rough surface is refined and the more asperities that can appear on the rough surface.The characteristic length scale does not affect the profile of the rough surface,but will change the height of the asperity.The higher the value is,the higher the height of the asperity.Reducing the frequency index,increasing the fractal dimension and decreasing the characteristic length scale all will increase the normal contact stiffness.(2)The rod fastening rotor-bearing system is taken as the research object.The rough contact layer of the discs is regarded as a beam element with only stiffness,and the dynamic model of the rod fastening rotor system with disc contact is established by the finite element method.And then,the Timoshenko beam element is used to establish the differential equation of motion of the system.(3)The fourth-order Runge-Kutta method is used for numerical solution,and the influence of disc contact,unbalanced faults,and structural asymmetry on the dynamic characteristics of the system are discussed.It is found that considering the disc contact and reducing the eccentricity will reduce the critical speed of the rotor system,and also decrease the system vibration amplitude.The change of system shaft length will also affect the critical speed of the system.Since rolling bearings are used,the vibration amplitude of the system suddenly decreases after crossing the critical speed.Considering the impact of the disc contact on the system vibration response is obvious in the resonance region.With the increase of the disc contact stiffness,the critical speed and the maximum vibration response of the system are gradually approaching without considering disc contact rotor system.(4)The rod fastening rotor-bearing system considering disc contact under misalignment fault is taken as the research object.The influence law of misalignment fault on the dynamic behavior of rotor system is discussed.Whatever considering the disc contact,the occurrence of misalignment faults will cause the rotor system to produce a sharp increase in the amplitude of vibration around its 1/2 critical speed.The critical speed has improved and the response amplitude has also increased in this sharp.In addition,misalignment faults will arouse the system’s 2th frequency,and when the system under low operating speed,the system will dominate the 2th frequency caused by misalignment faults. |
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