Computational Modal and Strength Analysis of the Steam Microturbine with Fluid-Film Bearings

The paper presents the results of the investigation of the dynamic and kinetostatic characteristics of a steam micro-turbine with fluid-film bearings. The object of the investigation was the rotor-bearing-casing system of the low-power steam microturbine designed for an ORC power plant. The bearing system comprised two identical slide bearings, which were lubricated with a liquid phase low-boiling medium, which was taken from the thermodynamic cycle of the power plant. The investigation was performed using the commercial the finite element method software ANSYS along with the MESWIR code package developed in IFFM PASci in Gdansk. The MESWIR codes were used to determine the dynamic stiffness and damping coefficients for the bearings at different rotational speed. Those coefficients were used in the computational modal analysis, being the second step of the analysis. Finally, the mode shapes and free vibration frequencies were determined for the analyzed rotor-bearing-casing system, along with the stresses for the rotor at nominal speed. The analysis of the obtained results reveals that the bearing stiffness affects significantly the dynamic properties of the microturbine which should not be neglected in similar analyses.