Analysis of thermal radiation effects on temperatures in turbine engine thermal barrier coatings

Abstract

Thermal barrier coatings on combustor liners and on turbine vanes and rotating blades are important for reducing metal temperatures in current and advanced turbine engines. Some coating materials such as zirconia are partially transparent to thermal radiation, and radiation within a coating will increase as temperatures are raised for higher efficiency engines. Hence, it is necessary to determine if radiation effects in a coating are a design consideration. For this purpose, the engine thermal environment is first summarized with regard to factors affecting radiative heat transfer. Radiative and thermal properties of zirconia are then considered, and methods of radiative analysis are briefly discussed. Typical temperature distributions and heat fluxes are given from the analysis of zirconia thermal barrier coatings on vanes and rotating blades, and on a combustor liner where the coating surface is expected to be covered with soot. The effects of various thermal conditions and heat transfer parameters are examined to indicate when radiation effects might be significant within a coating in a turbine engine. The largest effects were found in the combustor where coatings are subjected to large incident radiation. For coatings on turbine blades away from the combustor, and hence without large incident radiation, effects of radiation were found to be very small.