A fully coupled method for calculation of the entire flow in single- and twin-shaft industrial gas turbines is described. It is based on individual through-flow methods for axial compressors and air-cooled gas turbines developed by the authors that are coupled using simple combustion and cooling flow models connecting compressor and turbine flow paths. The through-flow computation for the analysis of cooled axial multistage turbines is fed by air from the compressor bleeds, which are part of the through-flow model of the compressor. The through-flow methods are based on a stream function approach and a finite element solution procedure. They include high-fidelity loss and deviation models with improved correlations. Advanced radial mixing and endwall boundary layer models are applied to simulate 3D flow effects. For air-cooled turbine analysis, various types of cooling air injection were adopted: film cooling, trailing edge injection and disc/endwall coolant flow. Compressor and turbine flow path computations were extensively validated individually and previously published by the authors.

The coupled method was applied to operation analysis and performance prediction of a newly developed industrial gas turbine in single- and twin-shaft configurations. In the latter case, the matching point of the compressor and high-pressure turbine has to be determined iteratively as a function of the compressor speed line, firing temperature, cooling and bleed-off characteristics, which may be important for strong part-load behavior. This process is explained in the paper.

Predicted gas turbine operation points are compared with experimental test data. It is demonstrated that the new method presented is an essential tool for overall gas turbine design and matching of the gas turbine components based on test rig experience. In addition, it is useful for diagnosis and supports the root-cause analysis of misbehaving field engines.

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