Compressors and turbines are an engine’s heart and muscle
Many consider the compressor to be the heart of any engine — and rightly so, because ultimately this component determines the power of every jet propulsion system. But efficient turbines are equally indispensable. In both cases, MTU Aero Engines has accumulated a wealth of experience in the past forty five years.
05.2015 | Text: Patrick Hoeveler
Patrick Hoeveler has been a member of the editorial team at aerospace magazine FLUG REVUE for some 15 years. His responsibilities there include the engines, regional aviation and history sections.
It all began with the development of the RB199 engine for the Panavia Tornado. “This was when we started to build up our skills in compressor engineering,” says Dr. Stefan Weber, who heads MTU’s department for technology and engineering, advanced programs. As a partner in the Turbo-Union consortium, the German company was responsible for the intermediate- and high-pressure compressor stages, a new departure for a company which until then had only manufactured engines under license. “The RB199 compressor had to satisfy a demanding spectrum of mission requirements. This project enabled us to build up solid experience in all relevant fields, including aerodynamics, mechanical engineering, modeling and design. The many tests carried out by MTU Aero Engines on the new compressor gave rise to theoretical and practical knowledge that is still being applied today.”
After the fighter bomber engine, the next military projects were the Eurojet EJ200 for the Eurofighter Typhoon and the Europrop TP400-D6 for the Airbus A400M. The EJ200 benefited from the use of improved 3D modeling techniques to optimize its aerodynamics and an integrally bladed rotor (or blisk) system that helped to improve the engine’s power ratio. Backed by this experience, the engineers then turned to commercial engine design. MTU gained particularly valuable insights while working on the HDV12 technology program, which laid the foundations for MTU’s entry into Pratt & Whitney’s PW6000 program, and during test runs of the ATFI (Advanced Technology Fan Integrator) geared turbofan demonstrator, in partnership with Pratt & Whitney Canada. These insights enabled MTU to make further improvements to its computer-assisted design methods, and ultimately assured the company of a stake in the successful PurePower® engine family of Pratt & Whitney. “We’ve been developing compressors since 1970, and during that time we have consistently improved engine efficiency. The EJ200 is roughly one percent more efficient than the RB199, and we have achieved another two percent in today’s GTF programs in collaboration with Pratt & Whitney,” says Weber. This might not sound much, but it’s a huge leap in the engine design world.
PRODUCTION OF COMPRESSOR AND TURBINE COMPONENTS AT MTU:
MTU was also responsible for the RB199’s air-cooled intermediate-pressure turbine, marking the beginning of MTU’s turbine development activities. Compared with compressors, MTU’s step from military to commercial engines was relatively short for turbines. The first was the low-pressure turbine for the PW2000, which was quickly followed by turbines for other engines, such as the best-selling V2500 that powers the Airbus A320 family and the GP7200 for the Airbus A380. Here too, the continuous improvement of design techniques resulted in greater engine efficiency coupled with lower weight and reduced noise levels. Among the new technologies that the MTU design teams had been developing since the early 2000s was the so-called high-speed low-pressure turbine. Gear units were integrated in the ADP (Advanced Ducted Propfan) and ATFI technology demonstrators to optimize transmission component speed. “Our turbine design enabled the low-pressure shaft to rotate faster than the fan, making it possible to reduce the number of turbine stages and thereby reduce engine weight and noise emissions. To achieve this result it was necessary to modify the design of the rotor blades and the disk on which they are mounted, thus improving their ability to withstand the higher centrifugal forces,” explains Weber. Titan aluminide, an extremely lightweight titanium-aluminum intermetallic compound developed in collaboration with Pratt & Whitney and other research partners played a decisive role in reducing the module’s weight. Its first application is in the high-speed low-pressure turbine for the PW1100G-JM engine that powers the A320neo.
Tests of the turbine as part of the Clean technology demonstrator attested to the viability of this approach. Further proof of concept was provided by flight tests of the Geared Turbofan™ demonstrator engine. “The high-speed turbine is the result of our continuous development efforts without which this engine might never have been built, and represents a major factor in the market success of the GTF family, which will also determine our success in the future. Looking back, we have been able to improve engine efficiency by an average of one-tenth each year, which places us among the international leaders in engine design.” MTU’s participation in German aerospace research programs has also been a contributing factor. And this is far from the end of the story: MTU’s specialists are continuing to work on improvements that will enable operating costs, fuel consumption and emissions to be reduced even further.