Simulation of Fluid-Structure Interaction in Last Stage of Steam Turbine

Turbomachinery blades are subjected to unsteady aerodynamic loads, which leads to their oscillations. This is especially relevant for the blades of the steam turbine last stages, which are up to 1.5 m long. The unsteady interaction of blade oscillations and the aerodynamic flow can lead to self-excited oscillations and, as a result, to structural failure. In this paper, a numerical method for solving the problem of unsteady aerodynamics of a turbine stage in a viscous gas flow and elastic oscillations of blades under the influence of aerodynamic loads is proposed using the modal method. A numerical analysis of the aeroelastic behavior of the rotor blade of the last stage of a turbine with a rotor blade length of 900 mm is performed. The analysis results show a possibility of stable oscillations with increasing amplitude for the first natural form of rotor blade oscillations, with a predominant frequency close to the first natural frequency. The proposed method for solving the coupled aeroelastic problem enables prediction of the amplitude-frequency spectrum of forced blade oscillations, which may lead to self-excited oscillations and onset of the blade flutter.