Ceramic and metallic stator blades for the high-pressure turbine
How can today's highly developed aircraft engines become even more efficient and environmentally friendly? How can higher combustion temperatures and corrosion resistance be realised while reducing weight at the same time? New materials and manufacturing technologies are an essential prerequisite for this.
Scientists from six different institutes and facilities of the German Aerospace Center (DLR) are working on the 3DCeraTurb project to develop new types of turbine blades based on two of the most promising new classes of materials: additively manufactured metals and ceramic fibre composites. A first important milestone has now been reached with the design of a standardised blade outer geometry that is suitable for the material and manufacturing process.
The objectives of the 3DCeraTurb project are to design and manufacture ceramic and metallic stator blades for a high-pressure turbine, to experimentally investigate the blades in the wind tunnel, and to evaluate performance, damage and durability for subsequent use in an aircraft engine. In this way, DLR is pooling its capabilities in the areas of new materials, design capability, component production and testing and evaluation expertise. On this basis, a basic process chain including design, production, coating, validation and life assessment for ceramic fibre composites will be established at DLR.
Potential of new materials and cooling concepts
The major challenge for materials used in aircraft engines is the extreme heat and temperature fluctuations. In order to increase the efficiency and effectiveness of engines, the trend is towards ever higher temperatures. Such temperatures can only be achieved with new, more temperature-resistant materials and improved cooling concepts. But production technology and design also play a crucial role in making a potential new material suitable for the desired application," says co-project leader Dr Michael Welter.
Additive manufacturing of metals promises particular advantages in the realisation of new, complex cooling concepts for engine components: This manufacturing process allows novel cooling geometries in the turbine, for example by removing the limitations of conventional manufacturing with regard to the shape and course of the film cooling holes. As part of the 3DCeraTurb project, DLR is therefore investigating new cooling technologies that are particularly effective and at the same time require less cooling air in order to further increase engine efficiency. Ceramic materials in particular, which have excellent high-temperature properties, promise to improve thermal stability. However, monolithic ceramics are less suitable for use as structural components in aircraft engines due to their inherent brittleness. Fibre-reinforced ceramics, known as ceramic matrix composites (CMCs), are of particular interest because of their damage-tolerant properties. SiC/SiC CMCs developed at DLR can currently withstand uncooled continuous loads of up to 1,250 °C, with further development potential for even higher temperatures. In addition, suitable protective coatings can reduce both the thermal load and the corrosive attack. The lower density of fibre-reinforced ceramics offers the potential to reduce the weight of the aircraft engine, thereby achieving an excellent thrust-to-weight ratio.
New manufacturing strategies for turbine blades
The project will also develop a process chain and manufacturing strategy for the production of turbine blades for both CMC and additive manufacturing. The complex blade geometry is a major challenge for CMC materials and manufacturing. The researchers are therefore focusing on transferring the manufacturing technology from flat samples to complex, full-scale components that will be used in aircraft engines in the future.
The manufacturing data of the ceramic fibre composites are also integrated into a high-fidelity multi-scale simulation, so that the life prediction models can be adapted to the manufacturing specifications. The traceability of the data generated will be ensured through provenance analysis. The DLR scientists are thus laying the first building block in a process chain in which the aspects of design, manufacturability and evaluation of the two future material classes are represented in detail.
Experimental long-term tests provide information on the service life of the blades
The manufactured turbine blades are analysed and evaluated for cooling efficiency and aerodynamic performance in the straight cascade wind tunnel at the DLR Institute of Propulsion Technology. The scientists are also interested in the service life of the different materials. To this end, the degradation mechanisms of the multi-layer systems are being studied in the temperature gradient test rig, the thermal cycling test rig and in a high-temperature furnace under a corrosive steam atmosphere, and compared with the results of damage calculations. The investigations also provide important insights for the use of hydrogen in the engine, e.g. regarding possible material embrittlement due to hydrogen corrosion.
At the end of the project, the technological maturity of the materials and technologies will be assessed for the ultra-high-bypass geared turbofan (UHBR-GTF) engine developed at DLR, which corresponds to a long-haul aircraft with a technology level of 2028 and is designed for a short runway length. Ultimately, we have to assess the technological maturity of the material concepts and the extent to which they are suitable for the requirements of the aircraft engine," says project manager Dr Anna Petersen.