Numerical Analysis of Flow Induced Vibrations of a Low-Pressure Steam Turbine Rotating Blade

Abstract

This paper presents the results of a numerical synthesis and characterization of vibrations of low-pressure steam turbine last stage rotating blades. A Fluid Structure Interaction (FSI) study is carried out using ANSYS Fluent 18.1 and ANSYS Mechanical 18.1. Using a one way coupling between ANSYS Fluent and ANSYS Mechanical, it was possible to link the two systems and allow pressure force calculations from Fluent to be used for the blade excitation in ANSYS Mechanical. The result of simulation shows that the blade exhibits vibrations which are characterized by amplitude modulation. An approximation for the equation of motion along the axial, radial and tangential direction was uncovered and fit. The three approximations for the blade vibration show a good agreement with results from ANSYS Mechanical. The effect of liquid mass (droplets) in the flow in the blade vibration was also investigated numerically. It is shown that increase in liquid mass is directly correlated with increase in the amplitude of the vibrations but has no effect on the frequency of the vibrations.