Research On Vibration Analysis Methods And Vibration Suppression Effect Of Damping Structure Of Blade

Blades are key components of turbomachinery, and they are often suffering servere vibrations violently under complex multi-field coupled boundry condition, and eaily cause fatigue and failure. In particular, blades using novel materials and adopting new structures for recent high-temperature, high-pressure, and high-power rotating machines are subjected to more severe vibeations and so does high cycle fatigue. So, in many engineering and therotical fields recently, it is significant to explore possible damping technologies powerful for blade vibration suppression.Diverse types of damping are proposed for blade vibration suppression, including friction damping at the dovetail attachment region, viscoelastic material damping at root, and hard coating damping at blade surface. Fundamental researches on three types of damping are carried out in this thesis, to obtain vibration analysis methods of blade damping structure, acquire its vibration characteristics, evaluate the effectiveness of vibration suppression of blade damping, and thereby achieve vibration reduction. Main contents are:Based on the finite element numerical method, effects of variation of the contact condition at the dovetail attachment region on dynamic characteristics of blade-disk are compared and analyzed. Simulation results show that friction coefficient of the dovetail attachment region and the rotation speed of the blade-disk have an important effect on contact pressure and sliding distance. With the increment of contact coefficient, both the contact pressure of the interface and the sliding distance of the contact edge decreased. While the contact pressure of the interface and the sliding distance of the contact edge increased as the rotation sped up. Natural frequencies of blade-disk with friction damping at the dovetail attachment region are lower than those when clamped.A novel method for vibration suppression is proposed, adding a viscoelastic damping block to the root of the blade. Using complex modulus model to represent the constitutive law of viscoelastic material, the analytical dynamic model of VE-blade is established. Subsequently, complex eigenvalue method is adopted to analyze the contributions of natural frequency, loss factor and response on the resonant frequencies and response level. With the thickness of viscoelastic damping block going up, natural frequencies decreased, loss factors increased while resonant response manifested different patterns.FE analyses on blade with viscoelastic material damping at root is then carried out after the FE method of viscoelastic material composite structure is confirmed. The complex constant model of viscoelastic material is adopted to represent the viscoelastic damping block at root to establish the finite element model of the VE-blade. Its natural frequencies and loss factors are then acquired with modal strain energy method. In addition, response is obtained through harmonic response analysis and vibration suppression effectiveness is evaluated. Justified by test results, FE model and numerical calculation method proposed here is applicable.A new method is proposed for vibration suppression to add hard coating on blade surface. Simplified mechanical model is adopted here as well. Motion governing equation of hard coating-blade is obtained based on the improved Oberst composite beam bending theory. First three order natural frequencies and steady response of hard coating-blade are obtained with analytical analysis. Comparison of natural frequencies and responses of blade system with and without hard coating is carried out. Test results proved the accuracy of numerical study above about the validity of hard coating on blade surface in vibration suppression.Based on the FEM of composite material structure and mechanics of anisotropic material to represent the hard coating, a finite element model of hard coating-blade is established. The influence of hard coating material properties (electromagnetic effects, thickness and coating position) on natural frequencies and harmonic responses are analyzed. Results show that after coating on the back of blade, frequencies of blade turned out to be higher. Coating thickness, piezoelectric and piezomagnetic effects have an obvious effect on high-order torsion and combined modes. Resonant response of blade decrease after coating on the back of blade. Moreover, compared to coating all over the blade surface, coating on the back only displayed better vibration reduction effects, with vibration stress decreasing more.Theoretical, numerical and experimental researches are conducted in this thesis on analysis method of vibration suppression mechanism, damping model and response level to keep down vibration of blade using friction damping at the dovetail attachment region, viscoelastic material damping at root and hard coating damping at blade surface. Analytical, numerical and test rests are compared and mutually confirmed, showing that all the three types of damping served an good role in vibration suppression. It is practical to apply these three damping technology to suppress vibration of blade, decrease the vibration stress, and improve the anti-vibration fatigue capability.