Cooling performance of film-cooling holes fed by channels of various shapes

Internal and external cooling is pertinent to maintaining operable surface temperatures of hot-section gas turbine components. Film cooling on the external surfaces is supplied from cooling passages placed inside of the blades and can affect the external film-cooling performance. Assessing internal cooling designs that were once difficult to investigate because of the complexity and costs of manufacturing cast turbine blades is now possible to more quickly and less costly through additive manufacturing (AM).This paper provides results and analysis of an experimental and computational study of the cooling perfor-mance of meter-diffuser shaped film-cooling holes fed by a range of individual channel shapes with different cross-sectional shapes: circle, hexagon, pentagon, ellipse, diamond, square, rectangle, trapezoid, triangle - vertex up, and triangle - vertex down. These geometries were made possible through the use of AM. The perimeter, and consequently the surface area of the supply channels to the cooling holes, was maintained constant between the different channel shapes. The predictive computational results showed that the shape of the channel affects the secondary flows through the hole that in turn affects the overall film cooling as determined experimentally. The triangle - vertex up created flow structures in the diffuser-shaped cooling hole that caused the coolant jet to create a film on the surface with wide lateral spread; whereas the triangle - vertex down created flow through the cooling hole that caused the jet to fully detach at the same blowing ratio. Consequently, the triangle - vertex up had a 14% improvement in overall effectiveness over the triangle - vertex down and a 33% improvement over the circle which had the lowest overall effectiveness of all the tested shapes.