28 October 2019

In the future, gas turbines will be more efficient, more eco-friendly, and powered by renewable fuel. They will also need less maintenance and be safer. At the Division for Solid Mechanics, models are being developed to predict the lifetimes of the materials that will make the future possible.

Daniel Leidermark, Christian Busse and Thomas Lindström. Photo credit: Mikael Sönne

Revolutionary research

Gas turbines are used to produce electricity and (rather simplified) can be thought of as huge vacuum cleaners. Air is drawn in at one end, compressed and heated in a combustion chamber. The heating process causes the air to expand, which forces the turbine blades to rotate, creating electricity from a generator connected to the other end of the turbine.

Thomas Lindström, Christian Busse and Daniel Leidermark are all studying, in slightly different ways, the materials that are to ensure that the turbines of the future perform better than today’s.

Gas turbine from Siemens.

“Some of the research we do is revolutionary, and we are the only research group in the world working on it”, says Daniel Leidermark, associate professor and supervisor for the two doctoral students Christian and Thomas.

Parts changed too often

Thomas Lindström conducts research into the materials (ductile superalloys) used in the turbine combustion chambers, manufactured by a new technique known as additive manufacturing (AM). It involves 3D printing and makes it possible to use not only higher temperatures but also biofuels in the turbines. It is, however, a new manufacturing technology that has many unknown variables, which is not the case for the traditional casting production method.

To be more precise, Thomas is constructing models to describe how the materials (nickel-based superalloys) behave in different conditions, not least during cyclical operation when a turbine is frequently switched on and off. The need for such operation increases when turbines are used to compensate for variations in the supply of power from wind-based and solar energy plants.

The researchers calls the samples in the tests "pacmans", due to their shape.

“It is possible to tailor the combustion chamber in a completely new way using 3D printing. The more accurately we can predict the behaviour of the material, the more exact will be the maintenance and service schedules used. As it is now, it’s necessary to use rather wide safety margins, which means that parts may be changed when it’s not necessary”, says Thomas Lindström.

Single-crystal materials

Christian Busse is studying single-crystal superalloys used at a deeper location in the turbine, in the blades of the disks that are driven by the heated air. While Thomas concentrates on how cracks arise, Christian’s doctoral thesis will examine how the cracks grow in different conditions. What appears to be completely random may in reality depend on the properties of the material. This means the growth pattern can be calculated and predicted.

“The interval between servicing can be made longer and the level of safety increased, when we know more about the materials”, says Christian Busse.

And what about the efficiency and fuel consumption: how much can this be improved?

“It’s clear that it can be improved, but it’s very difficult to say by exactly how much. And in many cases this information is held confidential by the manufacturers”, answers Daniel Leidermark.

Rolls-Royce´s jet engines

Crack formation in one of many tests.

The research of the two doctoral students is being carried out in close collaboration with Siemens Industrial Turbomachinery in Finspång. Their supervisor Daniel Leidermark, on the other hand, is a member of an international research group that is working with materials for jet engines in collaboration with manufacturer Rolls-Royce. The loads on an aeroplane engine differ greatly during take-off, flight and landing, and this is another type of cyclical operation that places huge demands on the materials.

The research project is working with an existing material, in which increasing the grain size is to improve its properties. Also here, one of the principal tasks is to create models to calculate how the material behaves under various loads.

“If we are successful, less material will be needed in construction and the fuel consumption will be lower. These are, of course, extremely important from an environmental point of view”, says Daniel Leidermark.

Daniel’s research concerns the disks to which the turbine blades are attached. These are manufactured from powdered material that is compressed under high pressure.

A superalloy is an alloy, usually consisting of nickel, nickel-iron or cobalt, that can withstand higher temperatures than normal alloys. Superalloys are often used in stainless steel.

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