Prize-worthy technology: MTU Aero Engines builds world-class low-pressure turbines
- High-speed low-pressure turbine for geared turbofan wins awards
Munich, May 30, 2017 - Low-pressure turbines that operate at maximum efficiency are one of MTU Aero Engines’ key areas of expertise. Indeed, the company has carved out a world-class technological position for itself in this field. Its technological breadth is enormous, ranging from conventional models for business jet engines and power turbines for heavy-lift helicopters all the way to large conventional low-pressure turbines for turbofan engines powering medium- to long-haul airliners. MTU’s masterpiece is the high-speed low-pressure turbine, a key component of the new PurePower®PW1000G Geared Turbofan™ (GTF) engine family, and a one-of-a-kind technology.
Low-pressure turbines are among the most highly stressed components in an engine, for they are exposed to extreme temperatures and speeds. “Their efficiencies have a significant influence on the overall fuel consumption of a turbofan engine. In terms of material selection and quality, this poses a tremendous challenge for its mechanical design and its production”, explains Dr. Stefan Weber, Senior Vice President Technology & Engineering Advanced Programs. MTU embarked on its first foray into this type of turbine technology already back in the 1960s.
Working on the RB199 engine powering the Tornado, MTU started its first in-house turbine-section development activities, assuming responsibility for the intermediate-pressure turbine in this engine program. The company’s strategic decision to expand its commercial engine business paved the way for MTU to become the global leader in low-pressure turbines it is today: When Pratt & Whitney started work on an engine for a new generation of medium-sized aircraft seating about 200 passengers, project nameJT10-D, MTU took on responsibility for the development and manufacture of the low-pressure turbine - for the first time in its history. To brace itself for the challenge, the engine company had participated in technology programs that allowed it to build the necessary technological capabilities. The new engine was renamed in PW2037, which was powering the Boeing 757 and the Boeing C-17 Globemaster military airlifter.
The five-stage low-pressure turbine of the JT10-D engine set new standards from the outset. Its efficiency was so impressive that it made quite a splash in the aviation community. As a result, when it came to selecting the right partner to make this engine module for a follow-on program - the V2500 - MTU was the natural choice. The V2500 powers the Airbus A320 family of jetliners and other aircraft and has grown into MTU’s most important commercial engine program. The company then took part in a number of other development programs for low-pressure turbines, such as the PW300 and PW500 engines for business jets, as well as the GP7000, which is the propulsion system for the Airbus A380 mega airliner.
A globally leading manufacturer
MTU today has made a name for itself for being among the world’s most experienced and technologically advancedmanufacturers of low-pressure turbines. Its range of products spans the gamut from conventional models for business jet engines, power turbines for heavy-lift helicopter engines, all the way to large conventional high-efficiency low-pressure turbines for turbofans powering medium- and long-haul aircraft. To maintain its leading position and remain a top player when it comes to highly efficient engines of the future, Germany’s leading engine manufacturer decided to make the high-speed low-pressure turbine one of its primary focus areas, making considerable self-financed investments and being supported by several national and international funding programs. With its high-speed low-pressure turbine for the geared turbofan (GTF), MTU has turned in its best performance so far and has developed a key component for Pratt & Whitney’s game-changing engine.
“To be able to join its partner Pratt & Whitney in building the PurePower PW1000G family of GTF engines, MTU has for many years consistently made considerable investments into the development of cutting-edge technologies”, says Dr. Jörg Henne, Senior Vice President Engineering and Technology at MTU. Among other things, it redesigned the new highly efficient high-speed low-pressure turbine from scratch and developed new design and computation methods to optimize engine weight and life, plus innovative constructions. A special focus is placed on new materials, such as titanium aluminide (TiAl)for low-pressure turbine airfoils or IN718DA for turbine disks. While the introduction of such materials is costly, they offer the potential of considerable weight savings. Investments have also been made into production engineering to reduce manufacturing costs.
Unique technology
The technology that goes into the high-speed low-pressure turbine is unique, and MTU is the only manufacturer worldwide capable of offering it for applications in commercial passenger aircraft. Compared with conventional types, this low-pressure turbine gives higher stage efficiencies as a result of lower aerodynamic loads. The high circumferential speeds allow higher stage work levels to be achieved, thus almost cutting the number of stages in half, which in turn permits a more compact design: The A320neo engine features no more than three low-pressure turbine stages. This affords a number of very important advantages: A reduced stage count results in significant weight reductions and considerably lower maintenance costs. Also, this turbine appreciably cuts perceived noise levels as compared with conventional ones, since it generates higher-frequency noise that is more rapidly attenuated by atmospheric absorption and is almost inaudible to humans.
Weber: “MTU’s high-speed low-pressure turbine moreover features novel, aerodynamically optimized 3D airfoils, which help further reduce fuel burn.” Given the decision in favor of a counter-rotating design of the high-pressure and low-pressure spools, it was possible to integrate the first low-pressure turbine stator stage into the turbine center frame to reduce parts count and cut down on weight while at the same time improving efficiency. Other technological highlights include 3D shroud contouring, a new casing concept for improved shielding from the hot-gas flow to appreciably reduce the amount of cooling air required and save fuel, as well as innovative, lighter materials for rotor disks and blades. The use of brush seals made by MTU allows the amount of cooling air and leakage in the area of the low-pressure turbine to be reduced, which again results in an improvement in fuel consumption.
Its unique high-speed low-pressure technology won MTU two German innovation awards: Shortly after the company was honored with the German Industry’s Innovation Award, it was also recognized with the German Innovation Award in the Large Companies category in 2013.
New material, new manufacturing method
The PurePower PW1100G-JM powering the A320neo plays a special role within the GTF engine family: For the first time ever, MTU used a new, additive manufacturing method, plus a new material, for this engine. The high-speed low-pressure turbine for the PW1100G-JM is the first one produced that comes with 3D-printed borescope bosses. They are part of the turbine case and allow the blading to be inspected for potential wear at regular intervals. Previously, these components were manufactured by casting or by milling from the solid; now, they are made by the selective laser melting method.
The second innovation is the third rotor stage of MTU’s three-stage, high-speed low-pressure turbine with specially made titanium aluminide blades. TiAl is a new, unique, intermetallic high-temperature material for highly stressed engine components in a class all by itself. The material was developed by MTU and its partners in the record time of a mere seven years. Its advantages: The lightweight material combines the properties of metallic and ceramic materials. As a result, turbine blades in TiAl are only half the weight of comparable nickel-alloy blades but boast the same reliability and durability. Its high aluminum content makes TiAl resistant to oxidation and corrosion. This is why it is the ideal candidate for applications under extreme conditions – high temperatures and pressures – such as those prevailing in high-speed low-pressure turbines.
Research continues unabated: The materials experts are busy developing an enhanced TiAl alloy. Their aim is to make more turbine stages from the new material. The innovation would be good news for the environment – for TiAl allows engines to be built that burn less fuel and hence use up less resources and are cleaner than today’s models.
Concepts for the future
For any new low-pressure turbine concept, the overall goal is to find a well-balanced design in terms of efficiency, weight, noise, costs and service life. To reduce the manufacturing and maintenance costs, MTU is exploring less complex, novel constructions. Dr. Jörg Eßlinger, Director Materials Engineering at MTU: “We are also looking at new lightweight materials for use at elevated temperatures. Materials play an important part in such new designs, as lightweight materials hold promise of saving up to ten percent of the overall turbine weight and reducing the amount of cooling air required, if not eliminating the need for it altogether.”Advanced computer simulations permit the three-dimensional design of the blade ducts, including side walls and fillet radii. For operation at the high altitudes at which long-haul airliners and business jets normally fly, improved airfoil designs and measures to selectively influence the boundary layer are being explored. To keep the noise the low-pressure turbine contributes to overall engine noise low a number of noise abatement measures, such as 3D contouring of turbine airfoils, are being investigated using an experimental turbine specifically built for the purpose.
About MTU Aero Engines
MTU Aero Engines AG is Germany's leading engine manufacturer. The company is a technological leader in low-pressure turbines, high-pressure compressors, turbine center frames as well as manufacturing processes and repair techniques. In the commercial OEM business, the company plays a key role in the development, manufacturing and marketing of high-tech components together with international partners. Some 30 percent of today’s active aircraft in service worldwide have MTU components on board. In the commercial maintenance sector the company ranks among the top 5 service providers for commercial aircraft engines and industrial gas turbines. The activities are combined under the roof of MTU Maintenance. In the military arena, MTU Aero Engines is Germany's industrial lead company for practically all engines operated by the country's military. MTU operates a network of locations around the globe; Munich is home to its corporate headquarters. In fiscal 2016, the company had a workforce of some 9,000 employees and posted consolidated sales of approximately 4.7 billion euros.
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