Analysis Of Natural Characteristics And Response Of Blade With Viscoelastic Damping Block And Contact Friction

Blades are key components of turbomachinery, and their safety and reliability constitutes an important guarantee for the safe operation. Service failures of blades can be attributed in many cases to high cycle fatigue cause by large resonant stresses. Viscoelastic material damping is an effective way to achieve vibration suppression and vibration stress reduction. At the same time, contact friction mechanism in the dovetail attachment region at root has a direct influence on the vibration characteristics of blade. Theoretical analysis of blade with a viscoelastic damping block (VE-blade) at root and in consideration of the effect of contact and friction are conducted based on vibration theory in this thesis. The results of the present study have laid a solid foundation for the design of blade and the analysis of their vibration characteristics. Main contents are:Reseach on vibration analysis methods of blade with a dampring block at root is carried out. Complex modulus model are used as the constitutive law of viscoelastic material, obtaining its stiffness characteristics. Analytical dynamic models of the blade with a viscoelastic damping block by SDOF based approach and cantilever beam based approach are developed. Analysis methods of natural characteristics of blade with a viscoelastic damping block is conducted. In addition, resonant response analysis of VE-blade with or without intrinsic damping is presented.Effectiveness of SDOF based and cantilever beam based models of natural characteristics are compared and analyzed. Justified by test data, both models and calculation methods proposed here are applicable, showing that natural frequencies decrease slightly while the response amplitudes reduce evidently when adding a viscoelastic damping block. Analysis of factors of natural characteristics and response of blade system is also conducted. With the increase of the thickness, storage modulus and loss factor of viscoelastic damping block, natural frequencies decrease and resonant response level drop, while loss factors increase, indicating a better vibraition suppression effect. In addition, the vibration reduction performance is weakened with an obvious decrease of modal damping ratios as the rotation speed goes high.Vibration analysis of blade in consideration of the effect of contact and friction at root is carried out. Normal stress at the interface is characterized with a spring and a viscous damping block and the friction force satisfying Coulomb's Law is introduced. A cantilever beam based model for blade in consideration of the effect of contact and friction is established. After the Galerkin discretion, forced response of blade under aerodynamic periodic excitation is obtained. Numerical calculation is performed to evaluate the effectiveness of vibration suppression of friction damping and acquire its response characteristics. Results show that friction damping at the dovetail attachment region has little influence on resonant frequencies and responses. This is verified by test results.