Life usage algorithms constitute one of the principal components of gas turbine engines monitoring systems. These algorithms aim to determine the remaining useful life of gas turbines based on temperature and stress estimation in critical hot part elements. Knowing temperatures around these elements is therefore very important. This paper deals with blades and disks of a high pressure turbine (HPT). In order to monitor their thermal state, it is necessary to set thermal boundary conditions. The main parameter to determine is the total gas temperature in relative motion at the inlet of HPT blades Tw*. We propose to calculate this unmeasured temperature as a function of measured gas path variables using gas path thermodynamics. Five models with different thermodynamic relations to calculate the temperature Tw* are proposed and compared. All temperature models include some unmeasured parameters that are presented as polynomial functions of a measured power setting variable. A nonlinear thermodynamic model is used to calculate the unknown coefficients included in the polynomials and to validate the models considering the influence of engine deterioration and operating conditions. In the validation stage, the polynomial’s inadequacy and the errors caused by the measurement inaccuracy are analyzed. Finally, the gas temperature models are compared using the criterion of total accuracy and the best model is selected.

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