Dynamic And Vibration Reduction Characteristics Analysis Of Turbine Blades With Dry Friction Damper

Blades are major components in aero-engines.Due to the complexity and severity of the working environment,vibration failure of the blade occurs frequently.Studing blade vibration characteristics,eliminating blade vibration failure,suppressing blade vibration so that improving its work safety is a key link of aeronautical engine technology.Attaching dry friction damper to the blade is an effective method for vibration reduction of the blade.Deeply studying the characteristics of dry friction contact interface and vibration characteristics and vibration reduction design technology of the turbine blade damper and controlling vibration stress level of the blade to a permitted range have an important theoretical significance and engineering application value.Theoretical derivation,mathematical modeling,numerical simulation and experiment of blades with dry friction dampers are performed in this paper,dynamic properties and related nonlinear characteristics of blades with dry friction dampers are invesgated.The main research contents and conclusions are reported as follows:(1)In this paper,the normal contact force and the resultant friction force at the contact interface is modelled as moving load,a more accurate model is established to describe the relative motion between the blade platform and the damper.Finite element method and modal superposition method are used to solve dynamic response of the blade-platform system.A numerical approach for solving the steady-state vibration of a simplified blade-damper system with nonsmooth friction contact is put forward and the flow chart of numerical calculation is given by using Matlab.Three distinct types of vibration between the two dampers and the blade platform surface and vibration reduction effect of the damper are studied using the established model.Numerical results show that: with the increase of the pre-load,the motion of the damper changes from full sliding state to stick-slip state,then to completely stick state when the pre-load is very high.The damper and blade platform form a new system when the pre-load is very high.There is an optimal pre-load which can make the biggest vibration reduction,the optimal pre-load exists in the stick-slip state.The optimal pre-load increases with the increase of the external excitation amplitude.(2)A lumped mass model of integrally shrouded group blades considering centrifugal stiffening of the blade,and rubbing and impact between adjacent shrouds is established.Equations of motion of the integrally shrouded group blades in different dynamic situations are derived,stick-slip-separation transition boundaries of adjacent blades are determined.Adopting this model,the effects of stiffness ratio?rotating speed and aerodynamic excitation amplitude on the vibration responses of the reference blade are investigated,and the effects of stiffness ratio? initial gap and contact angle for vibration reduction of the reference blade are studied.A normalised energy density is defined as a measure of vibration reduction effect.Numerical results show that: With the change of stiffness ratio,the reference blade can experience period 1,period 3,period 5,period 9 and chaotic motion.As the rotating speed increases,the reference blade will appear period 1,period 3 and quasi-periodic motion.As the aerodynamic excitation amplitude increases,the motion of the reference blade begins from the period 1 motion,then changes to period 3 motion,next changes to the quasi-periodic motion,and at last changes to the period 3 motion.When the initial gap is relatively large,the stiffness ratio has a great effect on the normalised energy density,however,when the initial gap is less than a certain value,the stiffness ratio has almost no influence on the normalised energy density.When the initial gap is less than a certain value,rubbing-impact between adjacent blades can occur.The normalised energy density decreases continuously at first,then increases with the increase of the contact angle,so there is an intermediate range of the contact angle which can make the best vibration reduction.(3)Adopting more practical linear spring and cubic nonlinear spring together to describe the contact stiffness between adjacent shrouds,and using an exponential dynamic friction model which is commonly used for contact between solid surfaces in dry conditions,a two dimensional lumped mass model of integrally shrouded blades considering centrifugal stiffening of the blade,nonlinear spring and rubbing-impact effect is put forward.Equations of motion of the integrally shrouded blade are derived.The effects of shroud gap,nonlinear stiffness ratio and aerodynamic excitation on the vibration responses of integrally shrouded blade are studied.Numerical results show that: With the change of the shroud gap or nonlinear stiffness ratio,the blade can experience period 1,period 2,period 3 and chaotic motion.Under symmetrical gap,as the shroud gap or the aerodynamic excitation changes,the blade can experience period 1,period 3 and chaotic motion.The reason for p-periodic(p=1,2,3,4)motion is that there exists a rubbing-impact period which is p times of the excitation period.Gap asymmetry leads to more complicated motions of the shrouded blade.Chaos occurs in certain bands which are separated by bands with p-periodic motions.(4)A method to analyze the coupled plane friction of two dimensional is preseted.The concept of friction force direction angle to determine the components of the static and kinetic friction vectors is introduced,stick-slip boundaries of the damper under two degrees of freedom coupled plane friction are given.The results show that the two degree of freedom coupled dry friction oscillator has stick-slip motion.When the excitation frequency and phase angle of x and y direction are not equal,the vibration chatacteristics of the vibrator will be more complicated.(5)In this paper,vibration and vibration reduction characteristics of the plane blades with underplatform and shrouded dry friction dampers are studied experimentally,comparison between the experimental results the numerical simulation results is performed.Experimental results show that: with the increase of the pre-load,the motion of the damper changes from full sliding state to stick-slip state,then to completely stick state when the pre-load is very high,this is in agreement with the results of numerical simulation;With the change of the aerodynamic excitation amplitude,the tip response of the shrouded blade appears with higher harmonics and some fractional harmonics of the driving frequency and bifurcation phenomenon as well.