Low-pressure turbine

Low-pressure turbines are a core competency of MTU. The technological band-width is enormous, extending from conventional low-pressure turbines for engines to power business jets, power turbines for heavy-lift helicopters, large conventional low-pressure turbines with high-efficiencies all the way to high-speed low-pressure turbines for the powerful geared turbofan.

The company hopes to consolidate its technology leadership long-term through technological prepara-tions for the successor generations of current engines.

The objective of technology development remains unchanged regardless of concept: it is to strike a reasonable balance between

efficiency
weight
noise level
cost
life.

Low-pressure turbine efficiency

Intentions over the next few years are to enhance the turbine efficiencies by reducing flow losses by as much as 15 percent, no mean feat when considering the high degree of efficiency already attained. This is hoped to reduce an aircraft's fuel consumption by 1.1 percent.

The availability of more computing power and new design programs will in the years ahead permit the three-dimensional design of the blade ducts, including side walls and fillet radii. In the process, numerical aerodynamic design optimization methods are used.

For operation at the high altitudes commonly associated with long-haul airliners and business jets, improved airfoil designs and measures to selectively influence the boundary layer will be explored.

Low-pressure turbine weight

Novel light-weight materials hold promise of saving up to ten percent of the overall turbine weight. While they are just as strong, rotor blades in titanium aluminum weigh only half as much as blades in conventional nickel alloys. This provides a tremendous weight-saving potential for low-pressure turbine blades for use at operating temperatures of up to 800 degrees centigrade.

Before one material can be exchanged for the other, however, numerous questions need to be answered. It is important to know, for instance, how the material holds up under operating conditions or what manufacturing process would be best to use.

Low-pressure turbine noise

In air traffic, flight noise is a limiting factor. Individual flight movements have indeed become less noisy over the past several years, but in all, their growing incidence is eating away at the improvement. The primary sources of flight noise are engines, undercarriage and the air enveloping the aircraft.

In accordance with ACARE targets, next-generation engines should provide a ten ENPdB improvement over current engines. That is a notable figure, considering that a ten dB or so difference halves the perceived noise.

To keep the noise low that the low-pressure turbine contributes to engine noise under certain operating conditions, such as approach, a number of noise abatement measures, such as the 3D contouring of turbine blades, are being explored using an experimental turbine specifically set up for the purpose.

Manufacturing costs of low-pressure turbines

The low-pressure turbine contributes significantly to engine cost. Depending on engine size and concept, its cost share amounts to 15 to 20 percent. In component development, MTU is exploring novel constructions to reduce complexity and concurrently looking at more cost-effective materials for use at elevated temperatures.