The flow-induced instability of high pressure rotors of large steam turbine generators has been a world-wide problem, and the subject of some controversy regarding the primary phenomena and major influencing parameters. In this study a simple one-dimensional model for the flow in a labyrinth seal was developed and solved for the linear dynamic coefficients. Dimensional analysis was employed to identify the major influencing parameters. The theoretical values for the dynamic coefficients were compared with published test data and found to be in qualitative agreement. Parametric studies were performed on typical sealing geometries to provide insight into the influence of the major design parameters on the aerodynamic excitation forces affecting rotor system instability. A computer program which utilizes the finite element method was developed for considering the effect of the flow-induced forces on the damped natural frequencies and linear stability of complex rotor systems. System damping was calculated for several high pressure rotor designs and the results compared with actual operating experience. The importance of the various system components (i.e. seals, blading, bearings, etc.) with regard to the overall system stability was evaluated by means of the relative energy per cycle.
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