Aeroelastic Behavior of Long Blades of Last Stage of a 220 MW Steam Turbine

Abstract

The phenomenon of flutter in steam turbines is quite rare, but when it occurs, the risk of damaging the blades and putting the whole unit out of service increases significantly. Currently, there is a tendency to increase the length of the blades of the last stages of powerful steam turbines, as a result of which the amplitude-frequency characteristics of the blade oscillations change, which can lead to the occurrence of uncontrolled self-excited oscillations. The paper presents the results of a numerical analysis of the aeroelastic characteristics of blade row of the last stage rotor of a 200 MW steam turbine, in which, during modernization, the length of the blades increased to 1200 mm, which made it necessary to check the resistance to flutter in operating modes. The analysis used the method of solving the coupled problem of unsteady aerodynamics and elastic blade vibrations, which allows to predict the amplitude-frequency spectrum of unsteady loads and blade vibrations in a viscous gas flow. The results of the calculations showed the absence of flutter and self-oscillations on the first five natural forms of blade oscillations in the nominal mode of operation of the steam turbine.