The next-generation aircraft
Designed with Simcenter comprehensive digital twins
By Jennifer Schlegel
A short 50 or 60 years ago, air travel was for an exclusive club of jetsetters – international high flyers, diplomats, time-is-money business executives, movie stars and the rich. Today, flying has become everyday. No longer for the happy few, the airline industry fulfills the crucial role of connecting people, goods and businesses.
Although the pandemic has thrown a wrench in the curve, so to speak, passenger travel volume should continue to grow steadily. Prior to the pandemic, experts predicted that the number of passengers traveling by air could be expected to double between 2017 and 2032. This may continue to slow down the next year or so, but it is likely that the current major dip will just be a temporary glitch. Air travel is here to stay. It has become a globalization cornerstone for more than 50 years and it will continue to play this role in the future.
A better flying machine?
Everyone knows that the aviation industry needs to change. We’ve come to a point where there is a scientific consensus that if no action is taken promptly, the global warming damage will be irreparable. The problem of global warming has led to international agreements on man-made CO2 emissions. This has resulted in legislation concerning all transportation industries. Combined, transportation is responsible for about 15 percent of the total greenhouse gas emissions worldwide. And even though aviation’s share in this is relatively small (around 2 percent of the total, or 12 percent of transportation), the industry suffers from a negative perception.
Radical new technologies will be required to reach the targeted reduction of 50 percent by 2050. In addition to biofuels and hydrogen fuel types, alternative airframe configurations and structural and material technologies, such as morphing wing technology, and electric and hybrid-electric aircraft propulsion systems show potential. Next to these environmental concerns, it’s important to mention the aviation industry has an additional incentive to improve energy efficiency and decrease its dependency on fossil fuels, especially for the commercial aircraft sector.
If you take the total cost of ownership of a typical Boeing model 737-800, over 50 percent is directly related to fuel. For aircraft operators, this is a huge financial burden and even a risk because fossil fuel prices can be volatile.
In addition to fuel consumption and emissions, noise and local air quality are part of the overall environmental impact of aviation. Electrification presents numerous advantages here. Electrical drives could reduce the rotational speed of propellers and fans, while maintaining propulsion power. Further, they could enable the application of distributed propulsion. This will allow engineers to experiment with the aircraft architecture and design fans that are shielded by the aircraft structure to avoid direct noise propagation toward the environment.
Finally, one cannot talk about aviation without a word about safety, still the number one design criterion in the industry. Even though flying is becoming increasingly safer, it can be better. Even the smallest incident can lead to a perception problem that affects the entire sector, especially today, with news spreading around the world at the speed of light.
Complex, electric, flying super-computers
According to the IATA Aircraft Technology Roadmap to 2050, we are currently in a period of evolutionary developments regarding aircraft as we know them: classic tube-and-wing-and-jet-engine configurations. Although experts predict that we could reach a new, more radical innovation wave by 2035, providing the economic framework is favorable. Today, we are still taking baby steps when it comes to aircraft electrification and design evolution, including innovative structural and material technologies. To be fair, there is still a lot of work to do before we can speak of a real industry transformation.
Besides radical changes in design, materials and propulsion, the next-generation aircraft will contain lots of automated systems that are man-made and therefore not immune to malfunction. Altogether, this can lead to a totally new dimension of complexity in the aircraft itself and the overall development process. Specifically, electrification in aircraft will lead to an enormous number of new systems, which often combine diverse technologies. That will undoubtedly challenge the aircraft integration problem even more, especially when working with various stakeholders in a global organization.
Designing the next-generation of electrified aircraft successfully will require innovative technologies and new development processes. A model-based engineering approach can help aircraft manufacturers and their suppliers deploy a comprehensive digital twin for performance engineering. This methodology facilitates behavioral verification and validation by using realistic simulation to more effectively tackle design complexities by removing silos between disciplines and applications, resulting in shorter development time and reduced risk. Together with the deployment of a digital thread, this leads to program execution excellence.
Work in progress
All this being said, there is already quite a lot of positive progress in regards to electrification and the next generation of aircraft. Power density, development process adjustments and digital twin adaptation are well underway.
Every kilogram counts on an aircraft. Today’s industrial electrical motors typically reach power densities of about 1 kilowatt per kilogram (kW/kg). That is simply insufficient. To successfully implement electric propulsion units (EPUs), this value would need to increase to at least 10 to 15 kW/kg. Apart from the motor, the same holds for subsystems, such as inverters.
Too many silos
A major issue in current aircraft development is that scale and complexity have led to programs being split up between various partners around the world. The division of work mostly happens as if an aircraft is an assembly of separable systems that can be integrated at a later stage. There is obviously a constant flow of communication between the various stakeholders, but often this is based on dead digital data, or other words flat documents that are shared throughout the organization. A good example could be the cooling budgets between electrical and ECS departments, which are usually described as flat numbers. Other examples can be found in thermal management and electrical system integration, amongst others.
Unfortunately, document-based engineering isn’t effective enough to get the results needed for successful electric propulsion systems. The power density this requires will generate thermal concerns, electrical system integration challenges and intensify the interaction between various physics. To handle these complexities, aircraft integrators will need to upgrade their development processes. This means changing from a siloed, static, document-based engineering approach to a dynamic model based engineering approach. The portfolio of Simcenter™ solutions offers a comprehensive set of scalable and collaborative tools for dynamic model-based performance engineering, from concept design to certification, all on one platform and traceable. This will enable consistent and accurate behavioral verification and validation throughout the design cycle.
A wide range of in-depth applications
The technological challenges in future aircraft development for aspects such as power density and thermal management will not be minor. To be a successful innovation partner, one cannot be a master of all disciplines. Quite the contrary, especially when the focus is on removing silos and creating comprehensive solutions, it is crucial to make sure state-of-the-art tools are available for every individual discipline.
To help this process along, Siemens has been investing in technology companies and their associated tools that have all the necessary pre- and postprocessing capabilities as well as robust and high-performance solvers, for a wide range of applications, and bundled them in the Simcenter platform to accelerate performance-driven engineering based on comprehensive simulation and testing.
Testing and the digital twin
During the earlier development stages, the value of the comprehensive digital twin approach is to a large extent defined by the degree of modeling realism that can be achieved. During this time, real measured data is vital to endorse modeling accuracy. Realistic simulation demands continuous testing work on components, materials, boundary conditions and more. This goes way beyond measuring accurate data for standard structural correlation analysis and model updating. Testing allows aviation engineers to explore uncharted design territories and build knowledge about new materials and all the additional parameters that come with mechatronic components. This often involves multiple physics and requires innovative testing methodologies.
At the end of the development cycle, especially during certification, the situation is different, as typically testing is then at the center of events. At this time, the pressure is on. Prototypes and testing infrastructure are costly to use, and late discovery of defects can directly impact the aircraft’s market entry. And with increasing aircraft complexity, including after-delivery updates, the share of work in this area can be expected to grow due to many more product variations, parameters, operating points, etc. At this stage, simulation can be a great addition and help to classic testing processes.
Indeed, virtual testing takes an increasingly prominent place in the certification process. But there are limits regarding airworthiness certificates. Authorities will always require evidence from integrators to prove modeling assumptions in simulations were correct. Therefore, Siemens strongly believes that it is best to investigate approaches where physical and virtual testing go hand-in-hand, and where cheaper and better verification and certification processes can be achieved. For example, simulation could help define the best test configuration. There are often huge opportunities to simplify physical test benches and complement physical testing aspects with simulated elements. This can lead to cheaper test setups or reduced testing risks.
In this sense, Simcenter is quite a unique environment as it is the only portfolio on the market that directly connects physical testing with system simulation, 3D computer-aided engineering (CAE) and 3D computational fluid dynamics (CFD). The Simcenter solutions portfolio, which is part of Xcelerator, offers aviation engineers a comprehensive set of scalable and collaborative tools for model-based performance engineering during aircraft development, from concept design to certification, all traceable and on one platform.