Acoustic fLow InteractioN over sound absorbing surfaces: effects on ImpedaNce and draG

Projektinformationen

LINING

ID Finanzhilfevereinbarung: 101075903

DOI

10.3030/101075903

EK-Unterschriftsdatum 1 März 2023

Startdatum 1 April 2023

Enddatum 31 März 2028

Finanziert unter

• European Research Council (ERC)

Gesamtkosten

€ 1 499 125,00

EU-Beitrag

€ 1 499 069,00

Koordiniert durch

POLITECNICO DI TORINO
Italy

Periodic Reporting for period 1 - LINING (Acoustic fLow InteractioN over sound absorbing surfaces: effects on ImpedaNce and draG)

Berichtszeitraum: 2023-04-01 bis 2025-09-30

Zusammenfassung vom Kontext und den Gesamtzielen des Projekts

Aircraft noise, from engines, jets, or air flowing over wings, is a major challenge in aviation. Reducing this noise is not just about comfort; it’s also about meeting strict environmental regulations and improving the quality of life for communities near airports. However, tackling this issue is complex. It requires a deep understanding of how air moves (aerodynamics), how sound behaves (acoustics) and how they interact, as well as the ability to design solutions that reduce noise without compromising the aircraft’s performance.
One of the technologies in this area is the acoustic liner, a structure with tiny orifices backed by a honeycomb structure and a rigid back plate, often seen at the front of jet engines. These liners are designed to absorb sound at specific frequencies, especially the loudest ones. But as aircraft engines evolve to become more fuel-efficient, like the new ultra-high bypass ratio engines, the nature of the noise they produce is changing. These engines generate lower-frequency and more broadband (spread-out) noise, which traditional liners aren’t optimized to handle.
This shift creates a need for new types of liners that can effectively reduce this broader range of noise while maintaining aerodynamic efficiency (i.e. not increasing drag or fuel consumption). However, designing these new liners is difficult, especially since even the behavior of traditional liners isn’t fully understood in all conditions.
The LINING project's goal is to deepen our understanding of how air and sound interact with both conventional and novel liner designs. By combining high-fidelity computer simulations with real-world experiments, the project aims to bring the relevant physics into the design process from the beginning, leading to better, quieter, and more efficient aircraft.

Arbeit, die ab Beginn des Projekts bis zum Ende des durch den Bericht erfassten Berichtszeitraums geleistet wurde, und die wichtigsten bis dahin erzielten Ergebnisse

The LINING project brings together researchers from across the globe thanks to the collaboration with institutions like NASA, the Federal University of Santa Catarina in Brazil, and the French aerospace agency ONERA. Together, they’ve made significant progress:
• Advanced Simulations and Experiments: The team has run high-fidelity numerical simulations and validated them with experimental data. These simulations help visualize and understand how turbulent air interacts with sound waves near the liner surface, especially at high speeds (high Mach numbers).
• Non-Intrusive Flow Measurements: Using cutting-edge tools like Laser Doppler Velocimetry, researchers can now measure both the airflow and the sound field over the liner without disturbing them. This provides a detailed, real-time picture of how the liner performs under realistic conditions.
• Facility Effects Matter: One surprising finding is that differences in airflow within test facilities can significantly affect results. This means that discrepancies seen in past experiments across different labs may not be due to the liners themselves, but rather to variations in the test setups. Understanding and controlling for these differences is crucial for accurate liner characterization.
• Manufacturing Precision is Critical: Even tiny imperfections, like a hole edge that’s slightly rounded instead of sharp—can change how well a liner absorbs sound. This highlights the importance of precision manufacturing and quality control in liner production.
• Toward New Design Tools: The team is also developing new numerical methods that, when combined with experimental data, will help engineers design the next generation of acoustic liners more effectively.

Fortschritte, die über den aktuellen Stand der Technik hinausgehen und voraussichtliche potenzielle Auswirkungen (einschließlich der bis dato erzielten sozioökonomischen Auswirkungen und weiter gefassten gesellschaftlichen Auswirkungen des Projekts)

One of the key discoveries from the LINING project is that differences in test results from various research facilities may not just be due to small variations in the geometries being tested. Instead, differences between the facilities flow field can have a big impact on the results.
This airflow affects how sound waves interact with the noise-reducing surfaces. In particular, the development of the flow field over the acoustically treated surface can explain why the measured impedance, the property used to characterize the liner, is different when the acoustic wave propagates in the same direction and in the direction opposite to the mean flow.
By identifying and understanding these factors, the LINING project is helping to improve how we test and design quieter aircraft technologies.

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