Large Eddy Simulation of Compound Angle Effects of Trenched Shaped Holes on Cooling Effectiveness

In advanced gas turbines, thermal barrier coatings (TBCs) are commonly employed as a passive technique to improve the cooling performance of the shaped holes. The application of a TBC often leads to the embedding of cooling holes within a two-dimensional trench cavity, which alters both the aerodynamic and thermal characteristics of the coolant flow. In this study, high-fidelity large eddy simulations (LES) were performed to investigate the influences of compound angle (CA) on film-cooling effectiveness and flow structures for a laidback fan-shaped hole embedded within a two-dimensional trench on a flat plate. The trench configuration was adopted from the authors' previous optimization work, which had identified an optimal configuration for enhanced thermal protection. Five different cooling hole orientations (CA0, CA15, CA30, CA45, and CA60) were analyzed using a three-dimensional compressible LES framework. The predicted film-cooling effectiveness was validated against pressure-sensitive paint (PSP) measurements conducted at the University of Bergamo for the reference case. The results reveal that the cooling performance and turbulent flow dynamics are strongly dependent on the cooling hole orientation within the trench cavity. Interestingly, the effect of compound angle on the coolant jet trajectory in the trenched holes exhibits an opposite trend compared with that reported for conventional nontrenched geometries in previous studies. Although the presence of a compound angle enhanced the cooling effectiveness on the cavity bottom surface in all investigated cases, the area-averaged cooling effectiveness on the downstream flat plate decreased with increasing compound angle. The CA60 case exhibited the lowest cooling performance, showing an approximately 7% reduction in cooling performance on the flat plate relative to the baseline configuration. The time-resolved analysis of the velocity field revealed that increasing the compound angle enhances the local velocity magnitude and intensifies flow fluctuations near the trench exit. This behavior promotes stronger interaction and mixing between the coolant jet and mainstream flow.