Coupled Transpired and Discretely Injected Films

NASA, and all users of turbomachinery, continuously requires improvements in engine durability and efficiencies. As combustion engineers push turbine inlet temperatures to new extremes, cooling designers are faced with increasing heat loads and less available coolant usage. Surface cooling techniques such as film cooling have proven invaluable in this quest. Films generated by forcing the coolant to bleed through a porous substrate have been shown to perform substantially better than discrete film injection in a thermal sense. However, the associated aerodynamic penalties limit the application. On the other hand, discretely injected films have drawbacks as well, including non-uniform coolant profiles significant mixing with the hot working fluid, lowering their effectiveness. Spectral Energies, LLC and the University of Central Florida propose a novel, low risk approach to surface cooling wherein traditional discrete film holes are embedded within a transpiring porous strip. The motivation behind this approach is multi-faceted, with the ultimate goal of developing a cooling arrangement which possesses the thermo-mechanical benefits of a transpired film, the aerodynamic benefits of discrete film injection, and mixing characteristics that are some compromise of the two.