Gas turbine operating state determination consists of the assessment of the modification, due to deterioration and fault, of performance and geometric data characterizing machine components. One of the main effects of deterioration and fault is the modification of compressor and turbine performance maps. Since detailed information about actual modification of component maps is usually unavailable, many authors simulate the effects of deterioration and fault by a simple scaling of the map itself. In this paper, stage-by-stage models of the compressor and the turbine are used in order to assess the actual modification of compressor and turbine performance maps due to blade deterioration. The compressor is modeled by using generalized performance curves of each stage matched by means of a stage-stacking procedure. Each turbine stage is instead modeled as two nozzles, a fixed one (stator) and a moving one (rotor). The results obtained by simulating some of the most common causes of blade deterioration (i.e., compressor fouling, compressor mechanical damage, turbine fouling and turbine erosion), occurring in one or more stages simultaneously, are reported in this paper. Moreover, compressor and turbine maps obtained through the stage-by-stage procedure are compared to the ones obtained by means of map scaling. The results show that the values of the scaling factors depend on the corrected rotational speed and on the load. However, since the variation of the scaling factors in the operating region close to the design corrected rotational speed is small, the use of the scaling factor as Health Indices can be considered acceptable for gas turbine health state determination at full load. Moreover, also the use of scaled maps in order to represent compressor and turbine behavior in deteriorated conditions close to the design corrected rotational speed can be considered acceptable.
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