Design Concepts for Low Aspect Ratio High Pressure Turbines for High Bypass Ratio Turbofans

The performance gains and weight reductions from using Ceramic Matrix Composite(CMC) turbine blades in both the High Pressure Turbine(HPT) and Low Pressure Turbine(LPT) will be determined. Shrouding HPT rotor blades becomes feasible when low density CMC materials replace current metallic HPT rotor blades. The proposal has two components. The first is to identify stage efficiency improvements and verify structural feasibility of shrouding a low aspect ratio HPT rotor blade designed to use CMC blades. The second is to perform similar analyses for metallic and CMC LPT blades . HPT stage efficiency gains will be determined using CFD analyses for shrouded and unshrouded HPT turbines as a function of clearance and stage reaction. The increase in blade component stresses due to the presence of a shroud, and the stresses in the shroud itself will be determined from structural analyses. Comparing analytic results with available structural data for shrouded metallic LPT blades will increase confidence in the structural predictions of shrouded HPT blades. The reduction in engine weight from using CMC blades in the LPT will be determined. Current metallic LPT blades are shrouded, so that no significant stage aerodynamic efficiency gain is anticipated from replacing metallic LPT blades with CMC blades. In a geared turbine fewer LPT stages, or greater work per stage, may be achieved from using CMC rotor blades.

This work will contribute to the NASA Aeronautics Program goal of increased gas turbine efficiency. Efficiency improvements contribute to the national goal of reduced CO2 emissions. The commercial application for N&R Engineering is to provide design and analysis services directly to NASA or to companies working with NASA to increase the TRL level for engine components that further the goals of the NASA Aeronautics program. The structural analysis capability of N&R Engineering will contribute to reduced fuel burn. N&R Engineering has extensive experience in the analysis of SiC/SiC CMC composite materials. Because these are light weight and high strength materials, engine weight will be reduced as these materials enter into commercial service. N&R Engineering will provide structural analysis services to NASA and other companies to achieve the reductions in fuel burn per passenger mile enabled by lighter weight engines. N&R Engineering is experienced in the analysis of cooling requirements for turbine hot section components. More efficient cooling approaches further the goal of reduced fuel burn.

Gas turbine manufactures, and other government agencies are potential markets for the services provided by N&R Engineering. These services are likely to be used for specific issues associated with the turbine hot section. N&R Engineering has an extensive background in the analysis of CMC materials for high temperature applications. The requirements for military aircraft engines are very sensitive to engine weight. Military agencies and their suppliers are a market for N&R Engineering services. Since gas turbines will provide an increasing share of domestic energy production, the Dept. of Energy is also a potential market for the services provided by N&R Engineering. These services will contribute to the national goal of increased fuel efficiency, and reduced emissions. N&R Engineering intends to provide analysis services to industry and government agencies for the design and analysis of CMC parts, such as vanes, blades, shrouds, and casings for gas turbine applications. Cooled ceramic materials show the promise of significantly improving cycle efficiency for both aircraft and land based gas turbines. Consequently, the market for N&R Engineering services is expected to be large.

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