Large eddy simulation of internal coolant crossflow orientation effects on film-cooling effectiveness of fan-shaped holes

Abstract

In modern gas turbine engines, the coolant is typically injected through the small cooling holes on the surface of the blade using an internal crossflow. Most experimental and numerical studies have used a stagnant plenum to feed the cooling holes without considering the influence of the internal coolant crossflow orientation. Therefore, in this study, we used large eddy simulations (LES) to investigate the effect of internal coolant crossflow orientations on film-cooling effectiveness and turbulent flow structures of fan-shaped cooling holes. A 7-7-7 laidback fan-shaped hole with an injection angle of 30-degree located on a flat plate surface was selected as a reference case. Three different internal coolant crossflow orientations (parallel/perpendicular with respect to the mainstream flow) were numerically conducted at a density ratio (DR) of 1.5 and two different blowing ratios (M = 1.5 and 3.0). The computational data were validated by the measurements of the reference case with a stagnant plenum in terms of flow and thermal fields. At both blowing ratios, the coolant channel parallel to the mainstream flow direction showed the best cooling performance among the cases. The coolant channel perpendicular to the mainstream flow displayed the minimum area-averaged film-cooling effectiveness, with a reduction of about 17% compared to the stagnant plenum. The velocity-field analysis showed an asymmetric pattern inside the cooling hole for the perpendicular coolant channel case due to the cooling hole entrance effect, which affects the distributions of film-cooling effectiveness on the flat plate. Furthermore, the time-space assessment of the velocity-field revealed greater flow unsteadiness and a wavy pattern for the crossflow perpendicular to the direction of coolant injection.