Gas turbine impellers free vibration study using the fem analysis
Keywords:turbine rotor, impellers, free vibration, finite elements method, vibration modes and frequencies
Due to the rather hard working process gas turbine engines rotor impellers are always heavily influenced by the unfavourable factors of the gas flow. So the close attention should be paid to the vibration processes in the rotor. More worse is the fact that the impeller consists of blades, which have a curvilinear geometric form. So they can’t be correctly described by the theory of plates or even by the plate finite elements. That’s why the problem can be solved only by the usage of space curvilinear finite elements on the base of which the mathematical model is built. The whole impeller can be considered as a cyclically symmetric system. Thus it can be divided into several sections, one of which would be studied. After the nonlinear FEM approximation of the aforementioned impeller’s section we receive a canonic matrix equation of the solid body vibration state. As in this study only the problem of the impeller free vibration is taken into consideration, than the matrix of damping and the vector of external forces are equal to zero. After making all necessary preparations, we find out the section free vibration modes and frequencies. All calculations were held for two types of boundary conditions that are chosen according to the impellers assembling schemes. Calculated results have been compared with the experimental data. As the divergence between them is less than 15%, than the developed mathematical model is adequate. The developed mathematical model and obtained results could be used for the gas turbine rotors forced vibration and stress-strain state study.
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