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Unsteady High-Lift Aerodynamics – Unsteady RANS Validation

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Advancing laminar wing technology for more sustainable aircraft

By maturing Krueger technology, researchers are paving the way to seeing a laminar wing flying on future transport aircraft.

Transport and Mobility icon Transport and Mobility

The global aviation industry is responsible for nearly 2.5 % of all human-caused CO2 emissions and 12 % of all CO2 emissions coming from all modes of transportation. As such, the sector is under increasing pressure to reduce its carbon footprint. Other than using alternative fuels such as sustainable aviation fuel (SAF), increasing aircraft efficiency is seen as one of the most promising approaches to decreasing emissions. In fact, according to the International Civil Aviation Organization (ICAO), improvements in aerodynamic, propulsion and lightweight material technologies have a direct link to reducing aircraft emissions. One of those technologies is laminar wing technology – a wing design that decreases friction and drag by enabling a smooth flow of air over the aircraft’s wings. “Laminar flow technology is seen as the biggest source of aerodynamic drag reduction, promising a significant reduction in fuel burn and CO2 emissions,” says Jochen Wild, a senior researcher from the Institute of Aerodynamics and Flow Technology at the German Aerospace Center (DLR). With the support of the EU-funded UHURA project, DLR led an industry effort to advance Krueger flaps. “These lift enhancement devices, which can be fitted to the leading edge of an aircraft wing, have the potential to be a key enabler of laminar wing technology,” explains Wild.

An extremely useful data set

To start, researchers looked at qualifying the simulation methods for predicting the unsteady flow of deflecting high-lift systems. “This phase was particularly critical as Krueger flaps tend to partially shield the wing against airflow, meaning a significant transient lift loss cannot be excluded,” says Wild. As there was no data available, to prove the validity of their simulations, researchers needed to create a database from wind tunnel tests and then compare these to their simulation results. The result of this effort is a globally unique source of unsteady data in the low-speed flow regime. “This data set will prove extremely useful, not only in future research efforts on the aerodynamic behaviour of Krueger flaps, but also for validating simulation methods,” remarks Wild.

Assessing critical unsteady flow features

Using this information, researchers turned their attention to discovering and assessing critical unsteady flow features. “We wanted to understand the sensitivities in different aspects of wing design, such as the impact of wing sweep and deflection speed, all of which could drive implementation,” notes Wild. One important discovery was that the wing sweep and three-dimensionality of the flow do not amplify lift drop. “This discovery highlights how the experimental and simulation data provides a very complete view of the impact Krueger flap motion has on an aircraft and the actions that need to be taken to ensure aircraft safety,” adds Wild.

Paving the way to a laminar wing

Having proven the feasibility of current Krueger flap design as a means of enabling laminar wing technology, researchers compiled guidelines for implementing the technology into aircraft design, including recommendations for system architectures. “The UHURA project successfully manufactured Krueger technology and helped remove some obstacles in its implementation,” concludes Wild. “In doing so, I am confident that we helped pave the way to seeing a laminar wing flying on future transport aircraft.”

Keywords

UHURA, data, aircraft, Krueger flaps, laminar wing technology, laminar flow technology, CO2 emissions, transportation, sustainable aviation fuel, aircraft design, aircraft wing

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