Vibration Characteristics And Fatigue Performance Analysis Of High Pressure Compressor Rotor Blades

The compressor is a kind of turbomachinery which takes the blade as the main working part,drives the rotor blade to rotate at high speed through the rotor shaft,works on the gas in the flow passage,transforms the input mechanical energy into the internal energy of the gas,and outputs the high temperature and high pressure gas.The rotor blade is the main working part,which bears high centrifugal force,aerodynamic force generated by fluid and exciting force from other parts of the machine,so it is easy to fail.The faults of rotor blades include cracks,dents,notches,missing angles,falling blocks,fractures,etc.The damage of falling block and fracture is especially serious.Because the rotor blade is in the working environment of high-speed rotation,the falling block or fracture may fly out along the tangent line,puncture the gearbox,or injure the blades of the same or later stage,causing secondary damage,or even cut the oil circuit,resulting in fire,seriously affecting the normal operation of the compressor.In this paper,the strength and vibration characteristics of the last stage blade of a gas turbine high-pressure compressor are analyzed through the finite element analysis.Combined with the actual operation of the gas turbine,the periodic exciting force of the blade is determined,and the Campbell diagram is drawn.It is found that the blade of this stage is excited by the wake of the first stage stationary blade to cause double torsion under the working speed the composite resonance increases the risk of blade tip fracture.In order to avoid the problem of blade angle dropping,this paper proposes a scheme of angle missing machining,which is verified by the finite element method.The frequency response of the two kinds of blades was analyzed by applying the same exciting force to the blade with and without angle.It was found that the maximum amplitude of the blade vibration after angle cutting was larger than that of the blade with failure,but the maximum Von-Mises stress was smaller than that of the blade with failure.In a word,the blade may have double torsional compound resonance at the working speed,and the maximum vibration stress of the blade under the dangerous excitation will be relatively reduced after chamfering.In order to improve the vibration fatigue strength of blades,the surface shot peening treatment is often used in engineering.In this paper,the effect of improving the fatigue performance of blades is studied by vibration fatigue strength test of blades without shot peening and after shot peening.In this test,the fatigue life of the first-order transverse bending vibration is compared.Through the S-N curve,it is found that the maximum stress level of the blade without shot peening in the middle life zone of about 1×10~6 cycle base is equal to that of the blade after shot peening,which is about740MPa.It is found that in the long life zone,the stress level of the blade treated by shot peening is higher than that of the blade without shot peening,and with the increase of the number of cycles,the difference between the two is larger and larger.Under the2×10~7 cycle base number,the median fatigue strength of the blade treated by shot peening is 35.8%higher than that of the blade without shot peening.Due to the influence of residual compressive stress after shot peening,the bending resistance of blade is improved,and the vibration fatigue strength of blade is greatly improved.To sum up,in view of the actual work of the last stage blade of a gas turbine,this paper analyzes the strength and vibration characteristics of the blade system,and determines that the blade angle drop is due to the fatigue fracture of the blade tip and trailing edge caused by the double torsional composite resonance caused by the wake excitation of the first stage stationary blade,and puts forward the scheme that the angle removal has avoided the fracture,which is verified by the finite element analysis.In order to further improve the fatigue life of the blade,this paper studies the effect of shot peening on the fatigue strength of the blade through experiments.It is found that shot peening on the surface of the blade body can significantly improve the fatigue strength of the blade body,which provides a strong support for engineering practice.