Comprehensive evaluation on conjugate heat transfer and thermal stress performance of film cooling

Abstract

Film cooling is a commonly used cooling technology in gas turbines, which could reduce heat load by spreading cooling air. However, it faces the problem of stress concentration in structures with holes. The present work focuses on conjugate heat transfer and thermal stress characteristics for a flat film cooling plate through an experimentally validated numerical approach. It discusses the effect of three geometry factors: inclination angle, compound angle, and ellipticity. An engine case simulation and a laboratory case simulation are compared to validate the analogy principle of conjugate heat transfer and thermal stress analysis derived from theoretical analysis. According to the analogy principle, the laboratory flat plate film cooling cases are set to conduct numerical studies. The maximum Mises stress of the film hole is equal to the product of the reference stress and the stress concentration factor. The reference Mises stress is proportional to the overall cooling effectiveness. The stress concentration factor is mainly related to the geometry of the film hole. Reducing the inclination angle of the film hole from 90° to 30° increases the overall cooling effectiveness and drastically increases the stress concentration factor from 2.7 to 5.5. Based on a cylinder hole with a 30° inclination angle, increasing the compound angle enhances the overall cooling effectiveness and slightly increases the stress concentration factor. Based on a cylinder hole with a 30° inclination angle, increasing the ellipticity increases the overall cooling effectiveness and reduces the stress concentration factor. With the increase of ellipticity from 0 to 4, the stress concentration factor decreases from 5.5 to 2. Elliptical film holes are ideal for future low-stress, high-cooling-efficiency turbine blades to extend the life of cooling vanes.