Noise reduction in a jet engine

In summary, the conversation discusses the use of atmospheric air mixing in jet engines to reduce exhaust noise. The increased speed of mixing allows for a higher frequency pressure wave, potentially outside of the human hearing range. This method is employed to lessen the shear between the fast exhaust air and slower relative wind, which is the main cause of noise in jet engines.
  • #1
nuub
9
0
I am in the process of writing a report on the Physics of Jet engines and I have come across a problem I cannot comprehend. In the exhaust of many jet engines they allow the atmospheric air to mix with the air from the engine to reduce exhaust noise. From what I understand this allows the gasses to mix faster, but why does this help reduce noise?

So far I think it is to do with the increased speed of mixing means that the pressure wave built up if of a higher frequency and so perhaps it is outside our hearing range? This doesn't seem quite right.

If anyone knows of how it actually works, or any other mechanisms that are employed to reduce noise please tell me.
 
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  • #2
Well this may be a little late, but I will give it a shot anyway. From my understanding what causes the vast majority of the noise from a jet engine is due to the fact that you have the very fast exhaust air and the slower realitive wind directly in contact with each other. This creates a strong shear and produces vast amounts of noise. So what they do is route some air around the acutal combustion chamber. This creates a very fast exhaust air surrounded by the medium speed air that was routed around the chamber, which is in turn surrounded by the relative wind. This lessens the amount of shear between any two levels of the air.

I hope that makes sense; I am terrible at explaining things.
 
  • #3
dronezero said:
I hope that makes sense; I am terrible at explaining things.
That sounded pretty good - welcome to the site.
 

1. How does noise reduction work in a jet engine?

Noise reduction in a jet engine works by implementing various technologies and designs that can reduce the amount of noise produced by the engine. These can include using sound-absorbing materials, modifying the shape of the engine components, and implementing advanced exhaust systems.

2. Why is noise reduction important in jet engines?

Noise reduction in jet engines is important for several reasons. Firstly, it helps to minimize the impact of aircraft noise on surrounding communities and the environment. Additionally, reducing noise levels can also improve the overall comfort and safety of passengers and crew on board the aircraft.

3. What factors contribute to the noise produced by a jet engine?

The noise produced by a jet engine is mainly caused by the high-speed exhaust gases exiting the engine, as well as the interaction of these gases with the surrounding air. Other factors that can contribute to engine noise include the design and shape of the engine components, as well as the speed and altitude of the aircraft.

4. How is noise reduction in jet engines tested and measured?

Noise reduction in jet engines is typically tested and measured using various techniques, such as ground-based noise monitoring, flight testing, and computer simulations. These methods allow engineers to analyze and evaluate the effectiveness of different noise reduction technologies and designs.

5. What are some challenges in implementing noise reduction in jet engines?

One of the main challenges in implementing noise reduction in jet engines is balancing the reduction of noise with other important factors, such as engine performance, efficiency, and safety. Additionally, implementing noise reduction technologies can also be a complex and expensive process, requiring extensive testing and research to ensure their effectiveness.

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