Extreme tests in the wind tunnel
Joint research for the aircraft of tomorrow
In order to make future commercial aircraft even more efficient, a research project that has so far been carried out in Germany is testing aerodynamic limits. But the phenomena are so complex that they require enormous effort to be understood. This is only made possible thanks to a brand-new cooperation.
International aviation has committed itself to becoming climate-neutral by 2050. To achieve this ambitious goal, a lot needs to happen, especially with regard to propulsion technologies. But there is also a lot of potential in the design of the airframe, both in terms of aerodynamics and construction. After all, the more efficient and lighter the airliner of tomorrow, the less fuel it will consume. What is important for the design is not the behavior under normal conditions but in extreme situations such as a stall at high speeds, the so-called high-speed stall. In this case, the wing loses lift and the aircraft sags. This can occur in very rare emergencies, such as when a jet is flying very fast and performs a sudden descent. How does the aircraft behave in such an extraordinary situation, and what stresses is it subjected to? These are precisely the questions at the heart of a research project launched in 2020. Despite all the progress made in computer simulation, the phenomena that occur are so complex that they have to be explored under realistic conditions in a wind tunnel.
On this side of the Atlantic, the European Transonic Wind Tunnel (ETW) is the only test facility suitable for this purpose, because the effort required to create flight-relevant conditions is enormous: High pressure (up to 4.5 bar) and low temperatures (down to minus 160 degrees Celsius) must be generated in the tunnel.
Due to the correspondingly high costs, to date only industry has regularly been able to use this infrastructure for product-related applications. However, the extreme complexity of the aerodynamic processes involved in a high-speed stall requires a high proportion of basic research, which aircraft manufacturers alone cannot provide. This falls more into the realm of university research, which, however, generally does not have access to facilities such as the ETW. However, since the current topic is so important for future innovations, a solution to this dilemma was needed.
Scientists from German universities and the German Aerospace Center (DLR) joined forces to address the issue with support from Helmholtz, the German Research Foundation (DFG) and Airbus. Helmholtz also provided extensive financial support to enable access to the ETW "Thanks to the community's commitment, scientists can study this highly complex physics under flight-relevant conditions at laboratory scale in the ETW on an Airbus model, using state-of-the-art measurement and simulation techniques from DLR. This direct collaboration between basic and applied research and industry is unique to date," says the head of the research group, Thorsten Lutz from the University of Stuttgart.
The success proves the researchers right: "The results are unique worldwide. The physical questions that can be answered, as well as the technical implementation, have gone far beyond the originally envisaged goals," explains project coordinator Lars Koop from DLR. Since the 1:37 scale model provided by Airbus closely resembles current products, the aircraft manufacturer can already incorporate data and insights gained into current development processes. "This real boost in innovation has also made big waves in ETW partner countries the UK and the Netherlands who are currently looking for ways to create similar opportunities for their researchers," says Guido Dietz, Managing Director of ETW. The cooperation thus serves as an exemplar across borders, and represents a possible template for further research topics on the journey towards climate-neutral aviation.