Numerical investigation on transient aero-thermal-structural coupling characteristics of curved double-wall structures during engine rapid load-varying process

The double-wall structure is a highly promising cooling technology for high-load turbines. However, existing designs of double-wall structures are primarily tailored for design conditions, making it difficult to maintain adequate cooling performance under off-design conditions. This is particularly critical during rapid load variation processes like acceleration, where issues such as transient cooling failure and localized stress exceedance may arise. Therefore, this paper focuses on the transient process of engine acceleration with rapid turbine load increase. Using the unsteady conjugate heat transfer analysis method, the study examines the curved double-wall configurations, which characterize the geometric features of vane curvature surfaces, to explore their aero-thermal-structural characteristics and variations in response to different rates of mainstream temperature rise and delayed coolant supply. The results indicate that the mainstream temperature rise during the transient engine acceleration process leads to significant alterations in both flow and cooling characteristics as well as stress behavior of the curved double-wall surface and within film holes, relative to steady conditions. During the process where the coolant supply increases correspondingly with the rising mainstream heat load, the concave and convex double walls exhibit similar improvements in overall cooling effectiveness in the upstream region. However, the convex double wall demonstrates a more significant enhancement in overall cooling effectiveness downstream due to the strong accumulation effect of coolant. At a mainstream heating rate of 5 K/s, the overall cooling effectiveness of the concave and convex double walls increases by 8.2% and 14.1%, respectively. Correspondingly, the discharge coefficient of concave double walls remains 18% - 22% lower than that of planar and convex double walls. For the three types of curved double walls, the mainstream ingestion and coolant discharge regions exhibit high stress. Although the secondary vortices within the film cooling holes weaken as the coolant flow rate increases, the instantaneous coolant impacts still cause continuous growth in hole-wall stress. The convex double wall consistently exhibits the maximum stress within the holes, while the concave double wall experiences the largest stress increase during the acceleration process. This study provides a theoretical foundation for the design of a highly reliable double-wall structure under rapid turbine load-varying conditions.