<p>The rotor-blade flutter phenomenon rarely occurs, but its consequences can be catastrophic. This concerns, to a greater extent, the blades of the last stages of steam turbines, which, due to their length and mass, have low natural frequencies comparable to the rotational frequency. This work investigates vibrations of the rotor blades of the last stage of a high-power steam turbine operating at a partial-load regime, excited by the unsteady flow from the stator blades and by flow nonuniformity in the exhaust hood. The flow–blade interaction was modeled by solving a coupled problem of aerodynamics and blade dynamics. Blade vibrations were modeled using a modal method. The numerical study was carried out using ANSYS Fluent with additional in-house software. The simulation was performed for the flow path containing all stator and rotor blades of the last low-pressure (LP) stage and a portion of the exhaust hood from the stage outlet to the condenser. As a result, unsteady aerodynamic forces acting on a rotor blade and its displacements under these forces were obtained. It was found that, on the first natural mode at an inter-blade phase angle near 270°, a steady growth of blade-vibration amplitude was observed; at an angle close to 180°, self-sustained oscillations of nearly constant amplitude were observed; for other angles, damping of blade vibrations was found. The amplitude variation was determined by computing the logarithmic decrement of oscillations. The improved method for modeling coupled rotor-blade vibrations produced a wider zone of regimes with significantly smaller aerodynamic-damping values – at which blade flutter may occur – compared with other methods.</p>