Reactant Film Cooling Strategy for Increased Turbine Blade Durability

Current combustors in gas turbine engines are releasing unburned fuel into the downstream components. These combustible species contact turbine blade film cooling air and undergo localized secondary combustion near the blade"s surface, resulting in increased temperatures, heat fluxes, and thermal stresses in the blades that significantly impact thermal fatigue and decrease turbine durability. While much research has been done on reacting fuel/air mixtures and non-reacting film cooling, the interaction of film cooling air with reactive freestream flows under realistic gas turbine conditions has not been adequately addressed by previous studies. The proposed work will close this knowledge gap by performing a detailed computational and experimental effort that will provide solid understanding and design guidelines addressing the effect of film cooling on blade wall temperature and durability. This understanding will enable the development of the proposed cooling strategy (fully explained inside) that will mitigate the impact of secondary, turbine-stage combustion on blade surface temperature, heat flux, and durability. The Phase I effort will include transient shock tube experiments with mixtures of high fuel concentrations and bleed air over various correlated geometries to measure wall temperatures and heat fluxes. A TRL 4 will be achieved at the end of Phase I. BENEFIT: The proposed technology has the potential to reduce energy consumption of the domestic transportation sector: The improved cooling strategy allows for higher combustor temperatures and stoichiometric ratios and increased thermal efficiency, and thus reduces energy consumption. Even in cases where the gas turbine combustor temperatures are not increased, more complete burning of the injected fuel will be achievable through local secondary combustions away from the turbine blade, increasing the amount of energy released for a given gas turbine and increasing thermal efficiency. The technology also has the potential to reduce the environmental impacts of the domestic transportation sector by minimizing the amount of unburned fuel exiting aircraft gas turbine engine exhaust, known to affect cloud formation among other environmental impacts. Unburned hydrocarbon (UHC) emissions can result from poor mixing, typically high with current short combustors with low residence time operating at high stoichiometric rates. Dual jet film cooling is an excellent method for mixing at least a portion of the fuel and air, and will thus reduce the unburned hydrocarbon emissions of any gas turbine engine. The approach proposed is an extremely practical and robust system that can be implemented onto any gas turbine engine with a capacity for compressor bleed air for film cooling. This project can provide economic benefit to US consumers in three main ways: (i) by the direct savings associated to more efficient gas turbine engines for commercial aircraft transportation, (ii) by the corresponding improvement in fuel emissions and the reduced environmental impact associated to a more reliable and efficient gas turbine engine, and (iii) by the potential to commercialize and export the proposed dual film cooled technology to foreign markets. The proposed technology is feasible and viable in the context of current manufacturing and design technologies for gas turbine engine film cooling. The approach is novel, yet the proposed solution is based on a design concept that can be manufactured with currently existing technologies at a reasonable cost. The proposed research has potential to have a substantially positive impact in the competitiveness of the domestic transportation sector since the dependence of commercial aircraft transportation in gas turbine engines is significant, and will be significant in the foreseeable future. More efficient film cooling and increased turbine blade durability are a key enabling technology to improve the competitiveness of the US commercial aircraft transportation sector.