Vibration Of Blade-Disc System Of Steam Turbine

Steam turbines serve as vital propulsion plants for power plant. An accurate analysis of the vibration characteristics of steam turbine's key components, blade, disc and the system as a whole is crucial importance for their research, design and running. Using three-dimensional finite element techniques, wave propagation theory, modals synthesis theory and numerical analysis methods, the vibration characteristics of steam turbine system are studied.According the structural features of practical blade discs, the 3-D 8-node element model is used because of its fitness to complex structures. The dynamic equations of blades for finite element analysis (FEA) were present. As the deformation caused by centrifugal force is beyond the small deformation range, the large deformation effect was also taken into account in the equation.Two models are constructed, one is of shrouded blade and the other is of bladed disc. The static natural frequencies and dynamic frequencies (under 3000rpm) are calculated by the finite element method and cyclic symmetry technique. The rotating vibration behaviors of the two models are compared. Different vibration characteristics between the two models are discussed.Geometry mismatch in a turbine blade root, which arose in manufacturing process or caused by wearing out during service, leads to contact conditions changed in fir-tree attachments. As a result, shifting of the fundamental frequencies and redistribution of stress in the blade base possibly cause failure of the blade. A three-dimensional finite element model of a blade and its fir-tree attachments have been constructed and analyzed with taking into account of contact nonlinearity in the attachments and large deformation effect of the blade. The geometry mismatch was introduced into the finite element model by defining gaps between two contact surfaces in the attachments. The influence of gap configuration and gap size on contact and fundamental frequencies was investigated. Results showed that gap configuration has significant influence on fundamental frequencies of the blade especially on its bending modes. Gap size has little influence on the frequencies but significant on the contact status and thus changes stress distribution in the attachments. The results also suggest that modeling contact behavior in fir-tree attachments is necessary to obtain more accurate fundamental frequencies.Cyclic symmetry in blade-disc assembles is often destroyed by small differences in the individual blades'structural properties that result from manufacturing and material tolerance, this phenomenon commonly knows as mistuning. In the present study, the effect of centrifugal force was investigated by three dimensional finite element analyses; the vibration characters of random mistuned blade-disc were also being investigated by probability methods and the Young's modulus of material of all blades are regarded as random parameters. The results indicated that the centrifugal force reduces the localization; when the Young's modulus of all blades are in the tolerance of 5%, the blade-disc can regarded as an cyclic symmetry system.The study results given in the present paper have provided a variety of effective numerical methods for the study of vibration characteristics of blade, disc and the blade-disc system. These research results can also serve as a helpful guide to the vibration study of other rotating components.