Understanding the off-design engine behavior is very important for the life cycle management of gas turbines because overhaul interval must be predicted accurately to minimize engine down time and maintenance costs. An off-design thermodynamic model has been developed for twin-shaft engines to obtain mean-line temperature distribution to be used in a prognostics system. A semi-empirical projecting approach was adopted to compute the two-dimensional temperature distribution for the gas path components. This temperature profile was then fed into the structural analysis and damage modeling modules of the prognostics system to predict the fracture critical location and crack initiation life of an A 250 integrally cast bladed disc (blisk). Comparison of the twin shaft model with GasTurb results showed that the model predicts the temperature profile within +/− 8K. The life prediction results from the prognostics system also match closely with the field data.

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