Film Cooling is the single most important line of defense that allows turbine components to function in temperatures that exceed the melting point of the alloys. Film-cooling holes are machined through the surface of turbine airfoils, and coolant air is bled from cavities within the airfoil, through the film holes, to form a protective layer between the airfoil external surface and the hot gas. At high blowing ratios, the coolant can jet or blow off, allowing the hot gas to cover the surface, resulting in reduced effectiveness.
Novel film cooling holes
Additive manufacturing has opened the doors to shift the paradigm in film cooling design because no longer do we need to limit our thinking to geometry that can be machines. Using an adjoint solver that morphs the mesh to maximize film effectiveness within some constraints, we can find novel shapes that result in enhancements of 40% compared to an aero slot (having constant cross section) and enhancements of 2.5X when compared with a conventional circular cooling hole.
Detailed measurements in a large-scale test facility.
Modeling film cooling flows is not easy, particularly at high blowing ratios where the film is likely separate and especially if we would like to use Reynolds Averaged Navier Stokes (RANS) methods for modeling turbulence. RANS is preferred because of its relatively faster run times compared to LES or DNS. The goal of this work is to obtain data at high spatial resolution to resolve the shear layers and wake region and other complex highly three-dimensional regimes associated with detached films with the goal of using this data to understand film cooling and validate/improve on CFD models.
Pulsating film cooling flow.
Film cooling flows are influenced by fluctuations or unsteadiness in the mainstream flow (due to rotor/stator interactions) or unsteadiness in the plenum feeding the coolant hole. Pulsating flows has been shown to be effective in reducing separation in other scenarios, so this work looked at whether there are any gains to be had in film effectiveness by pulsating the coolant flow.