Large eddy simulation of compound angle film cooling with round holes embedded in ginkgo-shaped craters

Film cooling holes embedded in craters or trenches are gaining attention as recent advancements in gas turbines due to significant improvements in film cooling effectiveness. Inspired by ginkgo leaves, a novel ginkgo-shape film cooling crater with two spreading lobes has been investigated using large eddy simulation (LES), achieving considerable enhancements in film cooling performance. A comprehensive evaluation of coolant film distribution and vortical structure variation is illustrated to understand the flow dynamics of compound cooling jets emerging from cooling holes embedded in the ginkgo craters at the blowing ratio of M = 1.0 and the density ratio of DR = 2.0. The film cooling effectiveness is greatly improved with compound angles of 0 deg and 30 deg due to the wide lateral expansion of coolant film and less coolant separation in the streamwise direction. However, the ginkgo crater deteriorates the cooling performance with a compound angle of 60 deg because of the enlarged uncooled gap between the adjacent holes. Instantaneous and time-averaged vortical structures are examined, showing that the upwash counter-rotating vortex pair (CRVP) and the asymmetric vortex (ASV) are greatly weakened. The origination and evolvement of the shear layer vortex and the hairpin vortex are discussed in detail with the effect of the ginkgo crater in the current work.