In order to keep a high efficiency of a gas turbine, it is important to make a suitable maintenance. Gas turbine nozzle guide vanes (NGVs) and turbine rotor blades deteriorate through a long-time operation due to various causes such as a particle attachment, erosion, and a thermal stress. In the present study, a numerical investigation has been carried out to clarify the influence of the NGV and the rotor blade deterioration on aerodynamics in a 3-stage gas turbine. Geometries of the NGV and the rotor blade were measured from a real gas turbine using a 3-D scanner. The first stage NGVs and rotor blades usually deteriorate seriously and are usually replaced at certain intervals. Two kinds of the geometries of the NGV and the rotor blade of the first stage were obtained, which are the new ones before use and the used ones to be replaced. For the second stage and the third stage, the geometries before use were used in the computations. The numerical results show that the isentropic efficiency of the first stage increases and that of the second stage decrease due to the deterioration of the first stage. The efficiency of the third stage is not affected significantly. The mechanisms are discussed from the observation of the flow fields.

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