Research On Dynamic Characteristics Of Rotor-blade-casing Systems With Blade Tip-rubbing

The clearance between blade tip of rotating machinery and inner casing is called blade tip-gap,which becomes one of important parameters affecting rotating machinery performance.In order to decrease internal medium leakage of rotating machinery and improve its work efficiency,the radial gap between the blade-tip and casing should be maintained as small as possible,which make rubbing between blade tip and inner casing easily occurs.Rotor-stator rubbing failure of rotating machinery is a highly nonlinear dynamic phenomenon,therefore research on the effects of rubbing in local or global damage and dynamic characteristics is of great significance.Taking a rotor-blade-casing system as the research object,this paper establishes a mathematical model of the system,and studied the complicated nonlinear dynamic characteristics of blade and casing under blade-tip rubbing by using the numerical simulation and model experiment.The main research contents in this paper are as follows:(1)Aiming at a rotor-blade coupling system,the kinetic energy and potential energy of the system are obtained,the differential equations of motion are derived by combing assumed modes method with Hamilton variation principle.In the model,the blade is simulated using Timoshenko beam considering the rotating effects of centrifugal stiffening,spin softening,Coriolis force etc;The disk is assumed as a rigid disk,and is simulated by a lumped mass model;The rotating draft is also simulated using a finite element model,and each element node has six degrees of freedom.(2)Natrual characteristics under the static state and rotational state and vibration responses of a rotor-blade system are compared with experimental results by using a test rig of a rotor-blade system,reults obtained from finite element model and the published literature.Through the comparision,the effectiveness of this model is verified.Moreover,the influences of diffrent parameter on the natrual characteristics are also discussed.The results show that frequency veering phenomena can be observed with the increasing rotational speed,the number of the blade coupling vibration modes is same as the blade number,and the coupling vibration modes of blade-rotor are also changing with the changing stagger angles.(3)Single-blade and multi-blade local rubbing due to rotor-casing misalighment are studied.Specifically,the influences of different parameters such as rubbing force model,rotational speed,casing mass,casing stiffness,blade number on rubbing induced responsesare discussed.The results show that for the single-blade rubbing,amplitude amplification phenomena appear when the multiple frequency of the rotating frequency coincides with the natural frequency of the rotor-blade system.For the multi-blade rubbing,amplitude amplification phenomena also be observed at the blade passing frequency(BPF),and the multiple frequencies of BPF have also bigger amplitudes.(4)By establishing a test rig of a rotor-blade-casing system,dynamic characteristics of the rotor-blade-casing system with rubbing is studied by comparing the simulated results with the experimental results.The results show that due to the effect of coupling between the rotor and blades,amplitude amplification phenomena appear when the multiple frequency of the rotating frequency coincides with the bending natural frequency of blade.In addition,amplitude amplification phenomena also appear when the multiple frequency of the rotating frequency coincides with the natural frequency of casing and rotor-casing coupling system.