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Researchers seek to reduce the impact of jet engine noise

17 March 2013

Virginia Tech’s College of Engineering is one of several US-based research teams tasked with finding a solution to jet noise as part of a three-year project.

Left to right: Tobias Ecker, Wing Ng and Todd Lowe at work on the test rig (photo: Virginia Tech)
Left to right: Tobias Ecker, Wing Ng and Todd Lowe at work on the test rig (photo: Virginia Tech)

This project is funded by the US Office of Naval Research’s Hot Jet Noise Reduction programme, related to a broader Navy initiative known as the Noise Induced Hearing Loss programme. The Navy’s goal: reduce noise exposure on the flight deck and its impact on the communities near air bases or in the path of jet flyovers. NASA also is partially funding the project.

“It is a subject that has received very little attention in the military world since it doesn’t improve military vehicle performance,” said Todd Lowe, an assistant professor in the Department of Aerospace and Ocean Engineering.

Yet it has created a problem of hearing loss and damage among military personnel, said Lowe. Measured in decibels – the intensity of sound perceived by humans – the Navy estimates that jet noise from tactical aircraft can reach 150dBA on the flight line as sailors and Marines prepare fighters and other aircraft for launching.

Lowe is working on the project with Wing Ng, who is a professor in the Department of Mechanical Engineering. Working on Lowe and Ng’s research team are Donald Brooks of Snowville, Virginia, and Tobias Ecker of Blieskastel, Germany, both doctoral students in the aerospace and ocean engineering programme.

Brooks built an $80,000 scale model hot jet rig – minus the engine – that simulates the noise of a fighter jet by forcibly pushing air through a small nozzle opening at speeds of around Mach 1.6. This movement of air and the turbulence it creates causes the roar that is associated with jets.

“The loudness is exactly the same as a real jet in flight, if heard from a properly scaled distance,” said Lowe. “For instance, our rig has the same loudness to an observer standing 1 foot away as an observer who is standing about 50 feet away from the real jet engine in flight.”

The jet rig entails a Sylvania 192 kilowatt heater that is larger and more powerful than similar models because it uses only one inline heater rather than multiple units, Brooks said. The change makes the apparatus smaller and easily portable.

“The idea was to have the ability to take the jet rig to other facilities such as anechoic test facilities to do more studies on the jet flow, without having to build multiple rigs in different locations,” said Brooks.

Lab tests are only the beginning of the multi-stage research project, begun last year. The second stage of the project includes a JT15D jet engine now housed at the nearby Virginia Tech Montgomery Executive Airport. There the stationary jet – built into a large scaffold – can be fired, with the blast noise and flow of air recorded, again, both by high-speed cameras and microphone.

A third stage may involve testing with stationary engines from F18 jets.

Once all data is collected, Lowe said the US Office of Naval Research will take the expertise and carry on the work in building noise-mitigation technology that will combine with ear protection. Lowe said the jet rig equipment may find additional lab uses, including the possible testing of heat on asphalt surfaces to mitigate melting.

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