NASA signs research agreement with DLR on aircraft noise reduction and funds supersonic flight studies
Future supersonic aircraft design concept from NASA research partner Lockheed Martin
Thu 25 Jun 2015 – US aerospace agency NASA and the German Aerospace Center (DLR) have agreed to collaborate on research into advanced methods for predicting aircraft system noise and establish validation guidelines for comparison between the two institutions. A reduction in aircraft noise without adversely affecting the environment or fuel efficiency is a major challenge, they say, but needs to be solved to enable further growth of air transport in the face of more stringent environmental challenges. Last year, NASA and DLR worked together with the Canadian National Research Council to study the effects of alternative aviation fuels at cruise altitudes on emissions and contrail formation (see article). NASA has also separately announced funding for research into quieter, greener supersonic travel that will address sonic booms and high-altitude emissions from supersonic jets.
Under the NASA/DLR project, each will run high-fidelity noise predictions on two virtual aircraft configurations – a model of an aircraft with overwing turbofans and another with turbofans under the wings. One of the key technologies for reliable noise prediction during new development takes into account all sources of aircraft noise and the impact of their installation, explain the partners. As the basis for noise prediction, acoustic measurement data will be used that was acquired by DLR in previous scientific flights with its now decommissioned Advanced Technologies Testing Aircraft System.
NASA and DLR signed a framework agreement in December 2010 on aeronautical research collaboration and have brought their respective scientific strengths together on several projects, including research into more efficient and environmentally-friendly aircraft, said DLR’s Rolf Henke.
Eight studies have been selected by NASA’s Commercial Supersonic Technology Project to receive a total of over $2.3 million in funding for research that the agency says may help overcome barriers to commercial supersonic flight. $1.2 million will go to a study by the Massachusetts Institute of Technology, which is being led by Steven Barrett, on the global environmental impact of supersonic cruise aircraft in the stratosphere. Other studies will look at sonic booms and low noise integration concepts and propulsion technologies.
Sonic booms – the loud report from a shockwave created by an aircraft flying faster than 660mph, the speed of sound at aircraft cruising altitude – were considered to be a public nuisance in the US and the FAA banned civilian supersonic aircraft from flying over land in 1973. The FAA has since been looking at changing this rule in the light of the NASA research, which shows the noise from booms can be significantly reduced. However, it has indicated that a change in policy would only be proposed if any future supersonic plane produced no greater noise impact on a community than a subsonic airplane.
In one of the studies to be funded by NASA, experts at GE’s Global Research Center will focus on reducing supersonic jet engine noise during take-offs and landings. Its engineers say the noise coming from high-speed aircraft, even at the lower take-off and landing speeds is a significant challenge that needs to be addressed.
“GE has developed extensive high-fidelity simulation tools and design concepts for noise reduction in our commercial and military engines, and we now plan to leverage that technology to reduce propulsion noise for this application,” said Kishore Ramakrishnan, principal investigator on the NASA programme and member of the Aerodynamics Lab at GE Global Research.
The sonic boom noise level of the supersonic Concorde was 105 PLdB. The PLdB that researchers believe would be acceptable for unrestricted supersonic flight over land is 75, but NASA wants to eventually beat that and reach 70 PLdB. Peter Coen, NASA’s supersonic project manager, said it was possible that smaller supersonic business jets could enter service sooner as lighter aircraft create weaker shock waves, which makes the low boom design challenge easier to solve.
“The business jet would probably be the first on the market, and that would help introduce some of the technologies that eventually would be used on the supersonic airliner. But such product decisions belong to others outside of NASA,” he said. “Our job is to support the science and technology behind those choices, eventually making supersonic flight available to the travelling public.”