Abstract
Ceramic thermal barrier coatings (TBCs) are used in power generation and aerospace turbines to protect superalloy components from large and extended heat loads. These coatings allow for increased inlet temperatures, thereby increasing efficiency and reducing air cooling requirements. Knowledge of the temperature profile in a thermal barrier coating is critical for evaluating the TBC performance and monitoring its health, as well as for accurate simulation and modeling. Non-contact, non-destructive techniques for finding these temperature profiles are highly desirable. Current techniques are limited in that they cannot measure the entire temperature profile of the TBC along with its radiative properties. An inverse radiative heat transfer method capable of determining the temperature profile, as well as the spectral absorption coefficient and spectral emittance at various wavenumbers, of a TBC using non-contact techniques was developed. A model of the measurements of the intensity exiting the TBC, which account for the emission from the substrate as well as the emission and absorption of the TBC itself, was developed. The TBC was approximated as a one-dimensional, plane-parallel, non-scattering medium. Optimization methods were used to determine the desired parameters by minimizing the error between actual intensity measurements and those calculated from the model. This method was tested for a number of simulated measurements with and without measurement error. Even with 10% measurement error introduced, the base temperature of the TBC was determined with only 0.45% error while the error in the TBC surface temperature measurement was 3.36% and that in the spectral emittance of the bondcoat was 12%. The error in the spectral absorption coefficient was significant.
Published Version
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