New lab techniques making aircraft quieter
Aircraft noise can be a serious environmental problem. It especially impacts people living near airports. One major effect is disturbed sleep. This leads to numerous health complaints, especially cardiovascular problems. Sleep-deprived people generally also have difficulty concentrating, which, for students, can lead to learning difficulties and disadvantage. Although some airports impose curfews, the restricted part of each day is very short. Daytime noise can also be stressful, causing further health problems. Additionally, the problem is getting worse. Air traffic has been increasing by 4.3 % per year. Although demand should continue increasing until at least 2038, concerns about noise pollution threaten this expansion. So, although today’s aircraft are 75 % quieter than those of 30 years ago, the industry needs still-quieter jets. The EU has set guidelines to be achieved by 2050.
New techniques and models
The EU-funded IMAGE project investigated methods for achieving the reduction. Researchers first developed new experimental and computational methods. Using these, the team then studied the fundamental physics of the two main types of aircraft noise. Engine noise is worst during takeoff, whereas airframe noise occurs most during landing (resulting from the turbulence created by protruding flaps and landing gears). The team also examined possible noise control mechanisms and strategies and focused on three aircraft technologies. The project developed the technologies’ readiness. IMAGE is part of a larger EU programme concerning projects that cooperate with Chinese partners in aeronautics. The project delivered six main outcomes. First was improved acoustic noise measurement techniques. One such method concerns acoustic liners, in this case meaning porous coatings for engine fan ducts. Improvement to computational methods consisted of mathematical models for studying fluid dynamics and aeroacoustics (CFD/CAA). “These methods can support industrial aerodynamic and aeroacoustic design and problem diagnosis,” says project coordinator Shia-Hui Peng.
Improved designs
Researchers applied the new measurement techniques and computational methods to predicting the effects of changes to engine and airframe components design. The components included acoustic liners, plasma actuators (electrical discharges with ionised air flow to control noise generation due to flow separation), and turbulence screens (wire meshes that suppress turbulence, a major source of noise). Newly designed turbulence screens resulted in an improvement of 3-4 dB, while the improved acoustic liners yielded reductions of 5-6 dB. “We have high hopes that our acoustic liners will suppress the noise emissions of engine inlets and outlets,” adds Peng. Another outcome was verification of the project’s low-noise fan blade and wing configuration concepts and testing of engine/wing interaction. A further legacy is a database of test case configurations, with and without noise control actuators, for CFD/CAA validation and, further, intended for use by future EU research projects. The team delivered a set of best practice guidelines concerning the use of CFD/CAA methods and the deployment of noise control technologies. Finally, the group’s technical assessment of the technologies illustrates the respective readiness and potential for industrial use in each case. IMAGE concluded in mid-2019. Some partners have joined new EU projects, where they will use and extend the methods developed in IMAGE. Other partners have also initiated their own bilateral partnerships. The industry does not operate super-quiet airliners just yet. However, IMAGE’s fundamental research brings them a step closer.
Keywords
IMAGE, aeroacoustic noise, aircraft, health, noise control, fundamental flight physics
