by Lauren Pafumi, FLC Midwest Region Support Office A team of researchers at NASA Glenn Research Center (GRC), Langley Research Center (LaRC), and Williams International has developed a metallic foam liner that reduces noise from aircraft engines. The team of Dr. Dan Sutliff, Dr. Cheryl Bowman, Mike Jones, and Tom Hartley worked against challenging time and cost constraints to create a technology that would enable commercial aircraft to meet increasingly stringent restrictions on aviation noise without adding to the size or weight of the aircraft.
Noise reduction is mandated by U.S. regulation and is part of GRC's key mission. The foam liner can reduce noise by up to four decibels. "Reducing aircraft engine noise can really improve the quality of life around airports," said Dr. Sutliff, the initiative's team leader. "If an engine is quieter, the distance [sound] travels will be less. If we reduce noise around four decibels, it would travel about half the distance before fading below the background." This would reduce by about 75% the number of homes affected by noise around an airport. The NASA team used a Space Act Agreement with Williams International to test its patent-pending over-the-rotor acoustic metallic foam liner on an FJ44 turbofan engine. NASA transferred the knowledge on the over-the-rotor liner design, as well as acquisition, processing and analysis of the acoustic data. In return, Williams built the liner and provided the engine test bed. The liner, which reduces noise by acting as a rotor-tip rub strip, previously had never been used in a full-scale turbofan engine, and the tests proved its viability. In June 2008, the team tested the liner on Williams' SB-class engine at NASA's AeroAcoustic Propulsion Laboratory and demonstrated its successful integration. Dr. Sutliff first began work on the foam liner in 2003 after seeing researchers testing small coupon samples at NASA's LaRC. The team at GRC first tested the foam in their low-speed fan in 2004, and soon thereafter published the results in open environments. NASA researchers first met with staff from Williams, who had read their published work, at a 2006 Ohio Aerospace Institute conference. "We laid out a project plan in about 15 minutes," said Dr. Sutliff. NASA's Partnerships Seed Fund Program, through the Innovative Partnerships Program, and the Fundamental Aeronautics Subsonic Fixed Wing Project provided funding grants for the foam liner project. The greatest challenge was getting the different organizations together in a short time, but the team's determination helped overcome any difficulties. According to Dr. Sutliff, the key participants were more focused on achieving their goals than adhering to restrictive protocols: "Everyone just pitched in and made it happen." Succeeding on a small engine clears the way for NASA to test the method on larger commercial aircraft engines, and the NASA team has taken steps to begin negotiations with several interested companies for these tests. While the current application covers a wide range of aircraft, successful implementation on larger engines would reduce noise in even more communities near airports. "We hope to convince some of the larger air engine manufacturers to investigate and join the research," said Dr. Sutliff. With more foam liner used to accommodate a larger engine, weight would increase relative to the engine's size. To address this, the NASA team is looking into methods of reducing the foam's weight for these applications. NASA also may be able to market the method for other applications in space propulsion and HVAC systems. One possible future use is large ventilation fans for HVAC systems. Because weight is less important in HVAC systems, adapting the foam to these fans would meet with few difficulties. The NASA team received a 2009 FLC Midwest Region Award for Excellence in Technology Transfer for its efforts.
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