Adiabatic Film Cooling Effectiveness of a LAM Fabricated Porous Leading Edge Segment of a Turbine Blade

Abstract

Laser additive manufacturing (LAM) is an emerging technology that builds parts in a layer-by-layer process by selectively melting metal powders. This additive manufacturing technique among others can produce very complex geometries, which are not possible using conventional methods. A mock segment of the leading edge of a turbine blade, designed with both internal and external cooling features fabricated by LAM of Inconel powder, is investigated. This design consists of an internal impingement cooling array and an engineered-porous structure. This porous region consists of a lattice of intersecting cylinders that simulates the effect of a transpiration cooled segment or permeable wall with a designed porosity of 0.57. Transpiration cooling is a promising external cooling technique capable of reducing thermal gradients at the surface of the blade by providing a more uniform film than conventional discrete film cooling holes. In this current study, adiabatic film cooling effectiveness is experimentally investigated using pressure sensitive paint (PSP) for blowing ratios ranging between 0.03 and 0.15. Using air as the mainstream, and CO2 as the coolant source, a density ratio of 1.5 is obtained. Steady state simulations using RANS are analyzed and used to compare against experimental results. All cases result in an increase in effectiveness values with increasing blowing ratio. Highest effectiveness values are associated with high pressure drop. Coolant uniformity is observed downstream the porous region and mixing becomes more significant as blowing ratio is increased.