Aircraft

Fin-lined nozzles could greatly reduce jet engine noise

Fin-lined nozzles could greatl...
Doctoral student Mohammad Saleem with some of the test nozzles – they were designed in a collaboration between the University of Cincinnati, the US Naval Research Laboratory and Naval Air Station Patuxent River
Doctoral student Mohammad Saleem with some of the test nozzles – they were designed in a collaboration between the University of Cincinnati, the US Naval Research Laboratory and Naval Air Station Patuxent River
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Doctoral student Mohammad Saleem with some of the test nozzles – they were designed in a collaboration between the University of Cincinnati, the US Naval Research Laboratory and Naval Air Station Patuxent River
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Doctoral student Mohammad Saleem with some of the test nozzles – they were designed in a collaboration between the University of Cincinnati, the US Naval Research Laboratory and Naval Air Station Patuxent River
Lasers and other equipment were used to observe and monitor the jet engine noise
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Lasers and other equipment were used to observe and monitor the jet engine noise
Doctoral students Mohammad Saleem and Aatresh Karnam work with a scale-model jet engine
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Doctoral students Mohammad Saleem and Aatresh Karnam work with a scale-model jet engine
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Whatever other qualities they may possess, jet fighters are not known for their quiet engines. They could soon become considerably less noisy without any loss in performance, though, thanks to a relatively simple alteration.

In tests performed within an anechoic chamber at the University of Cincinnati, aerospace engineers started by firing up a 1/28th-scale model of the F404 jet engine used in the F-18 fighter aircraft. Once they had established a baseline for the amount of noise created by its exhaust plumes, they tried swapping in different exhaust nozzles.

After some experimentation, it was found that a nozzle with a ring of small triangular fins on its inner surface altered the exhaust flow in such a manner that the perceived engine noise was reduced by five to eight decibels. That might not sound like much, but as lead scientist Prof. Ephraim Gutmark points out, "Typically, engine companies are happy even getting a half-decibel improvement because decibels represent a logarithmic scale."

Doctoral students Mohammad Saleem and Aatresh Karnam work with a scale-model jet engine
Doctoral students Mohammad Saleem and Aatresh Karnam work with a scale-model jet engine

Additionally, it was determined that use of the nozzle would not negatively affect the performance of the engine. In fact, the noise reduction could allow jets to last longer – in a phenomenon known as acoustic loading, planes can be literally shaken apart over time by the excessive vibrations caused by their engine noise.

Of course, quieter planes should also be easier on pilots and flight crews. According to the US Department of Veterans Affairs, hearing loss and tinnitus are the leading causes of military disability claims.

The US Naval Air Systems Command (NAVAIR) plans to test full-scale versions of the finned nozzles on F-18 Super Hornets, later this fall (Northern Hemisphere).

Source: University of Cincinnati

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8 comments
8 comments
Tag
Pretty cool. Reminds me of efforts to lower rotor noise from helicopters. We could all use some noise reduction features in a lot of the technology in our lives.
David
Bypass engines have been using mixers for many years. The fins mentioned in this article might function like vortex generators on wings.
Robt
Why only military engines?
Are they implying that the internal fins would not reduce the noise of a higher bypass turbofan?
Ed Clark
Really interesting research and a great goal. I live near an airport and would love to hear quieter jet engines. ;) Lowering the volume by 10db would be a game changer for everyone, keep working at it!
AlphaAaron
I wonder if anyone has arranged fins in a "rifling" pattern like a gun barrel. Perhaps sending the exhaust gasses out in a twirled patter would also reduce noise with little to no performance decrease. Maybe this experiment is the first step?
ljaques
I hope it can be modified to work with all airliner nozzles, too. 5-8dB is a really noticeable difference.
bahbah
The culprit for the intense noise of jet engines (especially in the high frequency range) is the shear tension between high speed exhaust in the nozzle shearing the much lower ambient air speeds. These triangular fins help to reduce the exhaust speed at the exhaust edges giving a more gradual speed differential. A coarse coating or a perforated edge in the jet exhaust might give similar results.
LarryStevens
Will it work for commercial engines?