A Conjugate Heat Transfer and Thermal Stress Analysis of Film-Cooled Superalloy With Thermal Barrier Coating

A conjugate heat transfer study is carried out to obtain temperature and thermal stress field of a film-cooled superalloy with multi-layer thermal barrier coatings (TBCs). The aim is to understand the effects of the blowing ratio and ceramic top coating (TC) thickness on temperature and thermal stress which have an influence on component reliability and life. Results reveal that the distribution of film cooling effectiveness gets more uniform as TC thickness decrease because thick TC with low thermal conductivity prevents heat conduction in the axial and spanwise directions. In the upstream of the film cooling hole, the cooling effect is enhanced nonlinearly with the increase of the blowing ratio since the flow separation in the tube affects the heat transfer enhancement. The insulation performance is improved by about 10 K for every 0.1D increase in TC thickness and the cooling effect is improved by about 20 K when the blowing ratio is increased from 0.5 to 1.0 at the leading edge of the film-cooling tube. The influence of jet lift-off and hot-gas entrainment on the insulation effect is greater than TC thickness. The stress concentrated at the leading edge of the film cooling hole and interfaces of TBCs. The maximum Von-Mises stress (752 MPa) on the interfaces is not at the leading or trailing sides of the film-cooling tube, it is about ± 45° from the centerline of the BC/SUB interface. The debonding stress at TC/BC interface and BC/SUB interface are about 26 MPa and 175 MPa respectively. The normal stress near the film-cooling tube on the BC/SUB interface is 5 – 7 times the one at TC/BC interface. Therefore, the interface crack is more likely to initiate at the BC/SUB interface, and the crack may keep growing and cause the spalling of TBC.

Keywords: conjugate heat transfer; thermal stress; film cooling; thermal barrier coatings;