Realistic Trench Film Cooling With a Thermal Barrier Coating and Deposition

Abstract

Thermal barrier coatings (TBC’s) see extensive use in high temperature gas turbines. However, little work has been done to experimentally characterize the combination of TBC and film cooling. The purpose of this study is to investigate the cooling performance of a thermally conducting turbine vane with a realistic film cooling trench geometry embedded in TBC. Additionally, the effect of contaminant deposition on the realistic trench was studied. The trench is termed realistic because it takes into account probable manufacturing limitations. The vane model and TBC used for this study were designed to match the thermal behavior of an actual gas turbine vane with TBC by properly scaling their convective heat transfer coefficients, thermal conductivities, and characteristic length scales. This study built upon previously published results with various film cooling geometries consisting of round holes, craters, an ideal trench, and a novel trench. The previous study showed that large changes in blowing ratio resulted in negligible effects on cooling performance. Changes to film cooling geometry also resulted in minor effects on cooling performance. This study found that the realistic trench and an idealized trench perform similarly. However, the width of the realistic trench left the vane wall more exposed to mainstream temperatures, especially at lower film coolant flow rates. This study also found that the trench designs helped to mitigate deposition formation better than round holes; however, the realistic trench was more prone to deposition within the trench. The overall cooling effectiveness was similar for both trench designs and relatively unchanged from the pre-deposition performance while the overall cooling effectiveness for round holes increased due to the additional thermal insulation offered by the unmitigated deposition.

A Comprehensive Understanding of Thermal Barrier Coatings (TBCs): Applications, Materials, Coating Design and Failure Mechanisms

“…Redesigning the configurations of the components, particularly those related to cooling mechanisms, can act as an approach to control overheating issues. Yet, this method is not always the easiest, least expensive or most effective option available [22,23].…”

Conjugate heat transfer modeling of a turbine vane endwall with thermal barrier coatings

“…Furthermore, round holes were found to show equivalent, if not better, overall cooling performance when compared to the trench holes. Later, Kistenmacher et al (14) also performed experiments to characterise the conjugate heat transfer effects of TBCs in conjunction with film cooling on a scaled vane model. On a low-pressure turbine blade platform, the improvement in thermal performance due to TBCs was evaluated by Mensch et al (15) .…”