Effects of compound angle on film cooling effectiveness considering endwall lateral pressure gradient

Abstract Film cooling is an important cooling method for the high-temperature components of modern aero-engines. There have been many previous studies on the influences of compound angle on film cooling performance, most of which are conducted in the ideal flat plate environment with zero pressure gradient, and the results indicate that at high blowing ratios, a large compound angle tends to improve the film cooling performance. However, in this work, it is found that a large compound angle tends to decrease the film cooling performance significantly with the influences of endwall lateral pressure gradient. A curved tunnel with constant width is employed to generate lateral pressure gradient similar to that in the endwall region of real turbine blade. It is shown that the crossflow near the endwall surface is the most obvious flow characteristic in this flow environment. Based on this discovery, we further conduct research on the influences of compound angles on film cooling performance in a curved tunnel both with numerical and experimental approaches. A well-designed laidback fan-shaped film cooling hole is used in this work. The experimental results show that for a film cooling hole with a large compound angle under blowing ratios ranging from 1.0 to 3.0, film cooling performance is reduced significantly under the environment of endwall lateral pressure gradient compared with zero pressure gradient environment. Detailed numerical results further indicate that due to the interaction between endwall crossflow and the strong single kidney vortex created by the large compound angle hole, large amounts of coolant are lifted away from endwall surface, which results in poor cooling performance. A topological model on the interaction between endwall crossflow and kidney vortices is proposed to help illustrate this phenomenon. The results of this work suggest that turbine cooling designers carefully consider the negative influence of large compound angles on endwall film cooling due to the lateral pressure gradient.