Advanced Geometries by Additive Manufacturing and Topology Optimization for Internal Cooling of Gas Turbine Airfoil

Abstract

In the past few decades, the growth in the ability of materials to retain strength at high temperatures has occurred remarkably slower than the rise in combustion temperature in gas turbine engines. With an aim to attain overall cycle efficiency of 65% in the next few years, the gas turbine inlet temperature is slated to reach in excess of 1700o C. As a result, there is a need to identify innovative and more effective cooling technologies for the hot gas path components, such as airfoils, to maintain them within their working thermal envelope. The presented research developed and demonstrated that advanced lattice geometries fabricated by direct metal laser sintering (DMLS) based additive manufacturing (AM) process could be effectively used in the cooling of gas turbine airfoils. The effect of unit cell topology, ligament diameter, and orientation with respect to fluid flow on the aerothermal performance of these geometries was investigated. In addition, a new type of integrated cooling architecture was also developed by combining AM fabricated transpiration and lattice geometries. This architecture could simultaneously provide external and internal cooling to the airfoils while also alleviating the harmful effects of pore blockage, which is a limiting factor with transpiration-based cooling. Three state-of-the-art experimental techniques and detailed numerical analysis were utilized to characterize the performance of these geometries. Finally, a new topology optimization (TO) method based on second law analysis was proposed to optimize the overall aerothermal performance of lattice geometries. Within this method, the relative strength of heat transfer and dissipative losses was calculated using local entropy generation rates. A set of criteria was proposed to precisely isolate high-dissipation fluid regions and modify them to suppress form-losses and improve local heat transfer, yielding the optimized topology. The proposed TO method presented several advantages: 1) the method could be implemented as a post-process script, thus eliminating the need for a custom solver, 2) optimization could be performed on prespecified geometries in a high Reynolds number flow, and 3) it provided a quantitative insight into the best operating point for a given geometry in terms of inlet flow conditions