Research On Damping Vibration Dynamic Characteristics For Shrouded Blades Of Steam Turbine

The dynamic characteristics of damping vibration for shrouded blades of steam turbine are mainly studied in this thesis. Combining the finite element simulation with experiment methods, the influence law of different damping structural parameters of shrouded blades on impact damping effect and friction damping effect is emphatically analyzed. Some preliminary exploration on the optimization design ideas and approaches for damping structure of shrouded blades are explored.According to features of steam turbine blades, the solid models of the different length blade with Z-shaped shroud are established. Afterwards, the natural vibration characteristics of single blade, grouped blades and whole circle shrouded blades are calculated by means of finite element analysis software, ALGOR. The effect of the clearance between the blade tips on natural frequencies and vibration modes of grouped blades and whole circle shrouded blades are emphatically analyzed. Meanwhile, the dynamic responses of damped vibration for grouped shrouded blades are calculated. The influence laws of such parameters as different primary clearance in tips, shroud contact angles, friction coefficients on contact surface, shroud contact stiffness and amplitude of exciting force on impact damping dynamic characteristics for integral shroud blades are analysized respectively. And then by selecting the two parameters, initial clearance in tips and contact normal pressure, the comparison analysis is made for impact damping effect and friction damping effect for medium-short straight blades and long twisted blades. Finally,a theoretical analytical model for calculating contact tightness in long twisted shrouded blades'tips is presented. The relations of the clearanceδin tips, shroud contact angleαand temperature field to contact tightness in tips are studied.An experimental system was set up to test dynamic response of damping vibration for shrouded blades, by which the shroud clearance and the initial normal load can achieve to adjust. Making use of the experimental system, the dynamic response for the first bending mode of the shrouded blades is tested, and the effect laws of shroud clearance, shroud contact angles, shroud initial normal load and exciting force amplitude on impact or friction damping effect for integral shroud blades are analysized respectively and contrasted. The results show that optimumly designing such damping structure parameters of shrouded blades as shroud clearance, shroud contact angles and shroud initial normal load is feasible, which validates that finite element calculation results are correct and lays the foundation for damping structure's optimization design of shrouded blades.Finally, the selection principle of damping vibration mode for different length shrouded blades is preliminarily discussed, and the reference method and design idea for the optimum shroud initial mounting clearance in impact vibration and friction vibration is presented. The research results have the guiding role in the optimization design of damping structure for the practical shrouded blades and have important engineering application in the design, safety and reliability of operation for the shrouded blades.