Degradation of Aerodynamic Performance of an Intermediate-Pressure Steam Turbine Due to Erosion of Nozzle Guide Vanes and Rotor Blades

Deteriorations of nozzle guide vanes (NGVs) and rotor blades of a steam turbine through a long-time operation usually decrease a thermal efficiency and a power output of the turbine. In this study, influences of blade deformations due to erosion are discussed. Experiments were carried out in order to validate numerical simulations using a commercial software ANSYS-CFX. The numerical results showed acceptable agreements with experimental results. Variation of flow characteristics in the first stage of the intermediate pressure steam turbine is examined using numerical simulations. Geometries of the NGVs and the rotor blades are measured using a 3D scanner during an overhaul. The old NGVs and the rotor blades, which were used in operation, were eroded through the operation. The erosion of the NGVs leaded to increase of the throat area of the nozzle. The numerical results showed that rotor inlet velocity through the old NGVs became smaller and the flow angle of attack to the rotor blade leading edge became smaller. Consequently, the rotor power decreased significantly. Influences of the flow angle of at the rotor inlet were examined by parametric calculations and results showed that the angle of attack was an important parameter to determine the rotor performance. In addition, the influence of the deformation of the rotor blade was examined. The results showed that the degradation of the rotor performance decreased in accordance with the decrease of blade surface area.