Article from DLRmagazine 170
Engines are the heart of the aircraft. Without them, these heavy, hightech birds would be grounded. DLR's aeronautics institutes have been working tirelessly for decades to refine engine designs. For some time now, the focus of research has been shifting towards the use of virtual models and simulations. DLR researchers Stanislaus Reitenbach and Kai Becker are convinced that simulations and digital models will prove indispensable for aeronautics in the future, particularly when it comes to engines. Reitenbach works in the Engine Department at the Institute of Propulsion Technology in Cologne, while Becker is working on developing the necessary platform at the Institute of Test and Simulation for Gas Turbines. Here, they explain the benefits of virtual engines, and how to get them into real aircraft.
What exactly is a virtual engine?
Reitenbach: Like many other industries, the aviation sector is undergoing a digital transformation. In this process, the complex systems of the real world, such as engines, are being transferred to the virtual world. A virtual or digital engine contains all the geometric and physical features of a propulsion system. To 'build' it, we use computer-aided design tools and numerical simulation methods while taking into account relevant disciplines, such as aerodynamics, structural mechanics and thermodynamics. We see this platform as a way to address multidisciplinary questions. It also allows us to calculate and evaluate the entire system on an ongoing basis. Ultimately, it should reflect all stages in the life and development cycle of a real engine.
Many specialist disciplines play a part in this design process. Who benefits from such models?
Becker: It depends. Generally speaking, you could say this benefits all those who have anything to do with an engine – from development and production through to testing and certification, and indeed manufacturing, sales and maintenance. We are also seeing great interest from industry. All the leading engine manufacturers are looking into this area. The form that the virtual engine ultimately takes will depend on the nature of the information needed by the user. Different methods provide different levels of detail; there are elaborate 3D simulations or less detailed performance calculations. We combine this information to create an appropriate model for each individual case.
That brings me to the question of the current state of research.
Reitenbach: Although this is still a relatively new area of research, we have already seen some ground-breaking developments. DLR is working on multidisciplinary simulation methods that can make highly accurate assessments about various aspects of propulsion systems, and these are already being used in industry for real products. In addition, we have developed a platform on which researchers from different scientific fields can work together on a model using a uniform database. To bring everything together, we have founded the Virtual Engine Technical Committee (FAVE) at DLR, where DLR’s aeronautics institutes advise on developments in this area.
Becker: DLR has been conducting research into many different topics for decades. What is new is that we want to focus on collaborative work and linking up the different product phases. It is no coincidence that DLR has founded institutes in recent years that focus on the field of virtual engines. In addition to the Institute of Test and Simulation for Gas Turbines, there are the Institute of Electrified Aero Engines, the Institute of Maintenance, Repair and Overhaul, and the Institute of Software Methods for Product Virtualization. The digital platform is also changing the way we work. We are moving away from the conventional sequential approach, where you start with the first phase, for example the preliminary design, and once that is completed, it is followed by the second phase – in this case the detailed design, and so on. Now that the individual disciplines are working closely together, several processes can run in parallel, and information is exchanged and stored across the different phases. This also allows us to access existing information if a new engine is to be developed. This is a very exciting advancement.
Are there any examples of a virtual engine already being used?
Becker: At my institute and in many other institutes we have test rigs that are designed not for the entire engine, but for components. Using a virtual representation of these components we can compare tests and simulations. We can then transfer the models to the overall system and observe the interactions between the components and their effects.
Reitenbach: Although DLR does not build aero engines, it supports both industry and its own research departments in all areas of the product lifecycle – in both design and production – using virtual engine methods. In addition to the test rigs, research groups are also working on predictive maintenance processes and digital twins. However, virtual engines are now a popular area of focus in the industry, as is clear from the numerous collaborations and new projects that have been launched in recent years.
How is the virtual engine linked to the real one?
Reitenbach: Ultimately, it is only indirectly connected to the real aircraft. There are two main aspects here, the environmental and the economic benefits. New, high-performance numerical methods and their use in a virtual model of the entire propulsion system help to improve real engines in terms of energy consumption and maintainability. In terms of economic benefit, the innovative and highly interconnected processes of the virtual engine enable us to significantly reduce the long and cost-intensive product development times, which involve very time-consuming and high-risk testing right up until market launch. Becker: It really pays off to look at the interactions between a wide variety of aspects, be it between different components or their impact, for example on overall efficiency and fuel consumption. This can then be measured against the goals that the air transport sector has set for itself, such as becoming more environmentally friendly.
Are there any limitations? In other words, are there instances in which you need a real engine?
Reitenbach: One thing is clear – a virtual engine alone is not enough to get an actual aircraft flying. Although the simulation processes and methods can already depict and predict many physical aspects, the test rigs, experiments and data from operations remain essential in meeting high safety requirements in future. Nevertheless, virtual engines can help to reduce the immense costs of real testing and complex maintenance processes. The virtual engine is not an end in itself, but a means to achieve the ambitious goals of the aviation industry.
Becker: It is a virtual representation – an amalgamation of digital information and numerical processes. Of course, this representation can only be as good as the quality of the simulation tools that are used to create it. To validate the numerical methods, I need experimental data – and I can only obtain this from a real engine.
It all sounds like a very challenging undertaking. What comes next? When will the virtual engine be usable as a tool for industry and research?
Reitenbach: We have our test rigs and we have our virtual methods. In the future, these two areas must be brought closer together. One term that comes up again and again in this context is the digital test rig. I believe that is where we are heading. Today, we are already in a position to optimise all the key components of aircraft engines in an interdisciplinary manner using highly accurate simulation methods. With each further stage of development, increasingly integrative methods and virtual operating scenarios, we are coming closer to a highly efficient, safe, quiet and almost climate-neutral engine. The virtual engine will be extremely helpful in addressing this extremely complex problem.
Becker: We also want to apply the concepts and ideas developed for this purpose to related areas of research. This interview was conducted by Anne Zilles. She works in programme coordination for digitalisation and supports the Virtual Engine Technical Committee on behalf of the Aeronautics Division.
This interview was conducted by Anne Zilles. She works in programme coordination for digitalisation and supports the Virtual Engine Technical Committee on behalf of the Aeronautics Division.