Thermal Analysis of Thermal Barrier Coatings at Elevated Temperatures

The development of next-generation gas turbine power-plants and aircraft propulsion is driven by the need for greater operating efficiency. One way to increase their thermal efficiency is to operate these systems at increased inlet temperatures with the use of Thermal Barrier Coating systems (TBCs). Desirable TBCs are functionally driven by their optimal thermal properties. The ability to characterize their thermal properties is critical to developing improved TBC systems and monitoring their performance throughout their service life-time. An emerging technique, Phase of Photo-thermal Emission Analysis (PopTea), has demonstrated the ability to measure the thermal properties of TBCs by probing the TBC with a CO2 laser and dynamically measuring the thermal response of the system. At low laser intensities the temperature within the TBC are on the order of unity above the reference temperature. However, decreasing the beam diameter and increasing the beam intensity will result in large thermal gradients within the coating. These large thermal gradients provide a environment in which the thermal properties extracted from the measurement are at significantly elevated temperatures. The thermal gradients within the TBC have required developing a model that is sensitive to temperature dependent thermal properties within the PopTea framework. This model was solved using a modified Crank-Nicolson finite differencing solver and the results were used to fit simulated thermal emission data to explore the thermal conductivity, volumetric heat capacity and optical penetration of the coating as a function of temperature.