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Monday 12 October 2020 13:34 PM

Designing the future:

The UltraFan^® demonstrator programme will present a fundamental breakthrough for civil aviation – here’s how digital technology is making it happen

In 1687, the British mathematician Isaac Newton published his three laws of motion. These include the notion that an object in motion stays in motion unless acted on by another force, such as gravity. The second law was that objects move farther and faster when they’re pushed harder.

Today, in civil aviation, we’re still bound by the same rules Newton first set out. But while we’re all limited by the laws of physics, human ingenuity has found opportunities to exploit.

And this understanding allows us to defy gravity.

The faster air moves, for example, the lower its pressure. So the wings on an aircraft are designed to pass air over the top sides faster, creating higher pressure beneath them, which is what lifts them up. Of course, none of that would work without an incredible amount of power to propel the aircraft forward. Harnessing this sort of power is a tricky business – but, for Andy Geer, Chief Engineer and Head of Programme – UltraFan, it is his business.

Pushing physics to the limit

According to Geer, there’s a simplified way to understand how today’s highly efficient turbofan jet engine works: by pushing a huge mass of air backwards to create forward thrust.

A large civil turbofan produces almost all its thrust through its very visible, very large fan. This fan pushes an enormous mass of cold air backwards at relatively low speed. Recently, new technology has allowed for this fan’s diameter to grow without increasing weight or incurring an efficiency penalty. This permits a larger engine to shift a higher mass of air at lower speed – the so-called ‘propulsive efficiency’ improvement.

Deep in the middle of the engine is a much smaller, power-dense core, which draws air through the fan root at the front into the engine’s compressor, where the air is pressurised. Fuel is mixed in with this compressed stream of air in the combustor – and then ignited. This dynamic produces an extremely high pressure, high temperature gas that flows into the rear-end section of the core, the hot turbine.

Next, the turbines extract energy from this hot, pressurised gas stream. The force keeps the core rotating, driving the thrust-producing fan. Improved technology in the core allows operation at higher pressures and temperatures where less fuel is needed to produce the required thrust – so-called “thermal efficiency”. This thrust is what allows aircraft to fly (in relative defiance of gravity).

But while we’ve long since cracked these basic mechanics of flight, there are many new challenges to solve. Now we continue to push physics to its limit to create, cleaner and more efficient engines – using digital technology to do so in both propulsive and thermal efficiency domains.

The primary challenge with which Geer and his team were tasked was how to make next-generation engines run more efficiently and reduce fuel consumption. According to Geer, we may be very near the limit in terms of efficiency for the current architecture of large aero engines.

In other words, we need to rethink the way we design them.

It’s a problem that’s top-of-mind across all of aviation, as targets for environmental improvements are tougher than ever.

“I firmly believe that few companies on the planet are better placed than Rolls-Royce to help solve this problem,” says our CEO Warren East.

“As an industrial technology leader, we want to use our capabilities to enable others to do the same. We will get our own factories and facilities there sooner, in 2030, but it is reducing the impact of our products – and particularly those that serve aviation – where the greatest challenge lies,” he adds.

Geer sought to answer this call – in anticipation of market demands – while designing the UltraFan, an engine concept now in development, which features a component new to large civil engines.

“Turbines are most efficient when they’re running at high speed and high temperature,” says Geer. “Fans are most efficient when they're running at low speed. Ultimately, you want to slow the fan down while still keeping the turbine that’s driving it running at high speed.”

Currently, our jet engines operate in ‘direct drive,’ so a shaft between the two turns both the fan and the turbine at the same speed. But to make an engine run more efficiently, the fan and the turbine need to move at different speeds. Fortunately, Geer and his team applied an elegant solution to this problem.

“To do that, you have to put a very high-power gearbox in the middle.”

While creating a power gearbox may seem simple enough, a jet engine is an elaborate system – and already very finely tuned. Adding a new piece to such an intricate puzzle was incredibly demanding. It represents a profound shift in jet engine design.

And cutting-edge digital technology, such as virtual modelling, helped make it possible.

4 facts about virtual modelling

1. Virtual modelling is a completely virtual representation of a component or part.

2. This technology can be used to build physical prototypes of the objects they represent.

3. This digital representation of these objects can serve as the basis for simulating both the fabrication process and the structural behaviour.

4. Virtual models have many applications across many industries – from video game development to architecture.

Virtual modelling and the cutting-edge of aviation tech

The difference between virtual modelling and simply designing something on a computer, according to Geer, is substantial.

“I think the difference is when you move to virtual modelling, you're extending that understanding into the functional domain,” he says. “In other words, [it’s] not only the geometry of the components, but how they operate, how they functionally interact with each other.”

A jet engine, says Geer, is a highly integrated system. All of the parts affect the performance of the other parts. So, to see how they work together, you need to run tests. By simulating and predicting its performance, virtual modelling allows conceptual engine designs to be tested before the physical realisation of those parts.

“In other words, you can model not only the geometry of the components, but how they operate, how they functionally interact with each other,” says Geer. “We’re in a position now where you can model very complex systems and their dynamic behaviour in real time - or closer to real time – and use that as part of your design practice.”

Basically, you don’t have to build the thing to see how it works. Armed with many terabytes of data, these models can predict how new designs will function, which Geer says was essential to developing the power gearbox for UltraFan. But he cautions that, for engine concepts this cutting-edge, full-scale engine models aren’t yet completely caught up.

“UltraFan is fairly new, so it's probably not a realistic expectation for the model to fully represent. You will get some surprises; you will get some emergent behaviour. If you're doing something that you've got lots of experience with and you're making relatively small modifications, then it's much more reasonable to expect that the model completely predicts the behaviour.”

Yet there is a lot more tech in Geer’s arsenal, such as Additive Layer Manufacturing (ALM), a kind of 3D printing.

“We sometimes use additive layer manufacturing to prototype the geometry right at the design stage,” says Geer. “We might start in an electronic digital environment, but then we might physically realise it in plastic.”

It’s a matter of going from digital into physical and then back into digital – and so on.

The IntelligentEngine vision

Our engine development now unites around a single vision: the IntelligentEngine.

“We are bringing the power of digital to shape everything we do in design, test, production and services,” says Chris Cholerton, President of our Civil Aerospace division. “Developments like these are ensuring that we make the IntelligentEngine deliver further benefits for customers.”

The UltraFan is a prime example of this vision coming to life. Because today, unlike Newton in the 17th century, our understanding of the physical world can be enhanced with digital technology. Engineers can now test new designs and concepts against millions of data points. And as this digital technology continues to improve, so too does our development of more efficient engines.