Research On Rotating Blade-Coated Casing Rubbing Induced Dynamic Characteristics

In recent years,wearable sealing coatings are used to reduce airflow leakage and radial clearance between rotor stators in aeroengines.However,due to the influence of centrifugal force,temperature,aerodynamic load and rotor vibration,too small tip clearance is also easy to induce blade-casing rubbing.The process of rubbing is very complex,which is accompanied by vibration,impact,friction and abrasion of coating.Therefore,the study on the complex vibration mechanism of blade and casing induced by rubbing is of great theoretical and practical significance for the clearance determination of blade and coated casing,the selection of coating materials and the detection of rubbing fault.Based on the theory of plate and shell and the finite element method,the dynamic model of the elastic supported blade and the finite element model of the coated casing were established in this paper.Considering the effect of abrasion of coating(adhesive wear,abrasive wear,cutting,micro-fracture and plastic deformation),a rubbing model of blade-coated casing was established.The effects of rotational speed,coating materials and support stiffness of the casing on the vibration response of blade-coated casing were discussed.The main research contents of this paper are as follows:(1)Based on the theory of plate and shell and the finite element method,a dynamic model of airfoil cross section blade with elastic support was established.The correctness of the model was verified by comparing with the experimental results and ANSYS results.Based on the discrete genetic particle swarm optimization and the agent model,the elastic stiffness of the blade was identified by the first three order natural frequencies obtained from the test.Based on the first four order natural frequencies of the tenon connected blade and the discrete genetic particle swarm optimization,the elastic stiffness of the blade was identified.Finally,the sensitivity of the first four natural frequencies to the stiffness in five directions(except rotational stiffness around the z axis)is studied.(2)Based on the 8-node shell element,the stiffness matrix and mass matrix of the laminated shell element were derived,and the finite element model of the coated casing was established,which was compared with the results of ANSYS to verify the correctness of the established model.The influence of abrasion of coating was ignored,and a rubbing model of the blade-flexible casing was established.The vibration responses of the blade-coated casing rubbing under different rubbing model(linear model,hysteretic contact force model and normal rubbing force model)assumptions were compared.Based on the hysteretic contact force model of the blade-coated casing,the vibration responses of the blade and the casing under different casing model(lumped mass model,cylindrical shell model and laminated cylindrical shell model)assumptions were compared.The effects of coating thickness,material,the support stiffness of the casing and casing length on the vibration response of the casing were discussed.(3)Considering the influence of abrasion of coating(adhesive wear,abrasive wear,cutting,micro-fracture and plastic deformation)on the rubbing process,based on the hysteretic contact force model,a blade-rigid casing rubbing model considering abrasion of coating was established.The correctness of the model was verified by comparing with the results of the literature.The vibration response of blade and abrasion loss of coating under different rubbing model assumptions were analyzed.Meanwhile,the effects of friction coefficient,Archard coefficient,coating hardness and elastic modulus of coating on the rubbing process of blade-rigid casing were studied.(4)Based on the laminated shell casing model,considering the time-varying effect of the mass matrix and stiffness matrix of the casing caused by abrasion of coating,a blade-flexible coated casing rubbing model was established.The effects of rigid/flexible casing on the vibration response of the system and abrasion of coating were compared.The effects of coating thickness,elastic modulus of coating,static misalignment,ellipticity of casing and support stiffness of the casing on the vibration response of blade and casing were analyzed.