Research On Rotating Blade-casing Rubbing Induced Vibration Response Based On Finite Element Method

In aircraft engines,distance between the rotating blade and the inner casing called small gap is a vital parameter which influences the performance and efficiency.In the modern aircraft engine design,in order to improve the engine performance,enhance the high thrust-weight ratio,the small gap is adopted,which may cause blade-casing rubbings,which usually induce the damages of the blade and the casing,or generate excessive vibrations of the rotor.Therefore,the investigation on blade-casing rubbing induced vibration response is very important.Based on the AN SYS software,taking rotating blade-casing as the research object,this paper establishes rotating blade-casing model,and investigates rubbing induced vibration response.The main contents include:(1)Based on the AN SYS software,four finite element blade models are established:a uniform thickness shell model(UTS),a uniform thickness twisted shell model(UTTS),a variable thickness twisted shell model(VTTS)and a solid element model.In order to verify the modeling method of these blades,the natural frequencies of these four blades are compared.Taking the solid element model as a reference model,the natural frequencies of other three blade models are compared.The results show that the errors between the natural frequency of the UTS,UTTS and solid element model are large.The natural frequencies of VTTS agree well with those of the solid element model.In addition,the vibration responses of these blades under aerodynamic force without rubbing are investigated.The result show that the dynamic characteristics obtained from VTTS model agree well with those obtained from the solid element model.(2)Assuming that the blade is simplified as UTS and UTTS model,considering the radial misalignment,angle misalignment and twisted angle,rotating blade-casing rubbing model is established.The effect of the stagger angle,angle misalignment and twisted angle on the rubbing induced vibration response are investigated.The result shows that considering the twisted angle,the resonance peaks occurs in the radial displacement of the blade-tip under the aerodynamic force;with the increase of the misalignment angle,the number of the resonance peaks and normal rubbing force increase;with the increase of the stagger angle,the amplitude of the radial displacement increases,and the amplitude of the flexural displacement decreases.For UTTS model,with the increase of the twisted angle,the amplitude of the displacement and normal rubbing force increase.(3)Assuming that the blade is simplified as VTTS model,the effects of the amplitude of the aerodynamic force,radial misalignment,stiffness of the casing,the number of the obstacle in front of the blade,angle misalignment and acceleration function in the rubbing induced vibration response are investigated.With the increase of the radial misalignment and casing stiffness,more resonance peaks occurs;the number of the obstacle in front of the blade influence the frequency of the dynamic force and the rotational speed of the resonance peaks;with the increase of the angle misalignment,the amplitude of the blade and normal rubbing force increase;the acceleration function has a little effect on the vibration response of the blade.In addition,the dynamic stress of the blade at 4 classic time are investigated,the results show that the VTTS model can predict the position of the maximum of the stress well,however,the errors of the value of the stress is large.(4)Assuming that the blade is simplified as VTTS model and the casing is simplified as shell,considering the effect of the deformation of the casing on the vibration response of the blade-casing system,the rotating blade-flexible casing rubbing model is established,and the effect of thickness of the casing and casing stiffness on the rubbing induced vibration response of the system are investigated.The results show that with the increase of the thickness of the casing and casing stiffness,the normal rubbing force and the amplitude of the blade displacement increase.