Jet Noise Reduction

Special thanks to The Clarion-Ledger

John Seiner, associate director of the National Center for Physical Acoustics at the University of Mississippi, checks out the installation of new engine flaps during testing at the Naval Air Warfare Center Division in Lakehurst, N.J. Seiner and his team developed the flaps to reduce engine noise from the Navy’s high-performance F/A-18 fighter jets. The new technology also may have applications in commercial aviation.

OXFORD — The window-rattling scream of high-performance fighter jets is a familiar sound for people living near many military bases, but acoustics researchers at the University of Mississippi have found a way to tone down the jets’ engine noise.

Scientists at the UM National Center for Physical Acoustics have found that small modifications to the engine exhaust nozzles can significantly reduce the noise produced by Navy fighter jets. In field testing, the modified nozzles also increased engine performance and showed promise to help aircraft elude missiles equipped with heat-seeking sensors.

The Office of Naval Research initiated acoustic suppression studies for F/A-18 fighter jets in 2002, providing NCPA with $2.5 million for the project. Led by John Seiner, the center’s associate director, the four-person team has made important advances.

“The engine test was successful,” Seiner said. “Not only did we completely eliminate the jets’ shock noise, we also experienced good infrared reduction while increasing the engine’s thrust.”

Seiner, a former NASA engineer, replaced flat seals on parts of the exhaust nozzle with corrugated ones. The seals keep hot gases from leaking into and damaging other parts of the nozzle when movable flaps, called internal divergent flaps, operate to maintain performance at various airspeeds.

The tests were done on F/A-18E/F Super Hornet aircraft. The team conducted a full-scale engine test using the new technology this summer at the Naval Air Warfare Center Division in Lakehurst, N.J. The results show the new seals reduced the aircraft’s noise by four decibels.

“Past research has successfully suppressed jet noise, but always at the expense of performance,” Seiner said. “This is a first in more than 50 years of research that the aircraft’s thrust wasn’t compromised.”

The study was funded to address community concerns in Virginia Beach, Va., after residents there filed a lawsuit against the federal government claiming their quality of life and property values declined because of noise pollution associated with the fighter jets. An estimated 2,000 homeowners surrounding the Naval Air Station Oceana in Virginia Beach are affected by various fighter aircraft, such as the F/A-18 Hornet and Super Hornet.

“The noise created by the F/A-18 is environmentally disruptive,” said UM researcher Larry Ukeiley. “On top of that, the Navy conducts night flights to simulate real-world combat, so the jets do awaken people.”

U.S. Rep. Ed Schrock of Virginia sought $30 million in appropriations to conduct such research in 2001. The bid was unsuccessful, but he’s pleased to hear about the UM research.

“The F/A-18 Super Hornet produces 118 decibels of noise, which is the equivalent of a rock concert,” Schrock said. “A reduction of four decibels would have a significant impact on noise issues related to our military aircraft.”

The technology also may have applications in commercial aviation, Seiner said. The concept may help quiet high-performance engines in airliners such as the Boeing 777.