Jet Sound Contribution to Shock Waves Near Supersonic Planes

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In summary, the sound emitted from jet engines during supersonic flight does not contribute significantly to the sound energy near the shock wave region. The "N-shaped" shock wave is caused by a rapid pressure drop and is considered one shock. While jet engines can produce powerful sounds, they do not contribute much to the shock wave from the aircraft's nose. However, the shock wave from the tail may be significantly influenced by the sound emitted from the engines. The main contributors to jet engine noise are fan noise and exhaust noise, which are both different in frequency and intensity.
  • #1
zoki85
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Typical supersonic airplane in supersonic flight creates 2 shock waves (2 Mach cones):
"N-shaped" shock wave.
How much of the "sound" energy near the shock waves region is contributed by the sound emmited from jet engines work?
 
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  • #2
I believe not much at all. The biggest sound in a jet engine (the screech as it goes over you) is from unsteady disturbances on the stators (or something like that, as I've been told).

The shock is merely a discontinuity in the flow, and is caused by the rapid pressure drop,raise,drop. Someone correct me if I'm wrong, but that N shock is considered one shock as well.

On a side note, there are various different sounds emitted from a jet engine, and they all produce characteristically different sounds.
 
  • #3
"N shock" is constituted of two Mach cones separated aproximately by a plane length (say 10..20 m in aircraft's vicinity).
Imagine theoretical aircraft with completely silent engines propagating supersonic.It creates two Mach cones.
Real aircrats are also source of a sound created by the work of its' propulsion engines.If you ever heard stationary work of such engines they can be source of a VERY POWERFUL SOUND!
Considering shock wave from the aircraft's nose they don't contribute nothing at all.Considering the shock from tail they can contribute and I think they may contribute quite a lot!
Another thinking is what is contribution in between two Mach cones.
Are my questions clear?
 
  • #4
I forget the exact physics of the particular sounds, but there are two major "sounds" that are emitted by the engine. There is the "screech" you hear as a plane passes directly over you (I'm talking subsonic right now, but it should apply). If you've ever sat near an airport, you know what I'm talking about.

The properties of these unsteady waves allow it to spread at an almost right angle when it leaves the engine. Now, after a couple of seconds, you hear the low rumble. This is a completely different family of pressure waves. Those are higher amplitude, but much lower frequency.

I may be completely wrong, but I think at 50,000ft, the enormous pressure discontinuity would overwhelm effects from the jet engine.
 
  • #5
The two main contributors to jet engine noise are fan noise and exhaust noise. Fan noise is usually dominated by a single frequency component that is a function of things like tip speed, blade geometry and number of blades. Exhaust noise is highly random and is pretty much as broad band frequency as you can get.
 
  • #6
FredGarvin said:
The two main contributors to jet engine noise are fan noise and exhaust noise. Fan noise is usually dominated by a single frequency component that is a function of things like tip speed, blade geometry and number of blades. Exhaust noise is highly random and is pretty much as broad band frequency as you can get.
Thank you for the reply.
Note that my question wasn't about mechanisms and types of sounds emmited by the engine.
It's about to what extent that sound magnify effect of the shock wave of supersonic aircraft.
 

Related to Jet Sound Contribution to Shock Waves Near Supersonic Planes

1. What is the significance of jet sound in causing shock waves near supersonic planes?

Jet sound is a major contributing factor in the formation of shock waves near supersonic planes. As the plane moves faster, the air in front of it gets compressed, resulting in a high-pressure region. When this high-pressure air is released behind the plane, it creates a loud sound known as a sonic boom. This boom is a type of shock wave that can cause damage to structures and disturb people and animals on the ground. Therefore, understanding and controlling the jet sound is crucial in reducing the impact of shock waves near supersonic planes.

2. How does the design of a supersonic plane affect the production of jet sound?

The design of a supersonic plane plays a significant role in the production of jet sound. The shape and size of the plane's engines, as well as the placement of the exhaust nozzles, can affect the intensity of the sound produced. For example, a longer and narrower exhaust nozzle can help reduce the intensity of the sound by allowing the exhaust to expand more gradually. Additionally, the overall aerodynamics of the plane can also impact the production of jet sound and shock waves.

3. Are there any regulations in place to control the jet sound from supersonic planes?

Yes, there are regulations in place to control the jet sound from supersonic planes. In the United States, the Federal Aviation Administration (FAA) has established noise standards for supersonic aircraft. These standards limit the maximum noise levels that can be produced by supersonic planes during takeoff and landing. Additionally, certain areas have restrictions on supersonic flights to minimize the impact of shock waves and jet sound on nearby communities.

4. Can advancements in technology help reduce the impact of jet sound on shock waves near supersonic planes?

Yes, advancements in technology have the potential to reduce the impact of jet sound on shock waves near supersonic planes. One approach is to develop quieter engine designs that produce less intense jet sound. Another strategy is to use specialized materials and structures that can absorb or redirect the shock waves, reducing their impact on the ground. However, further research and development are needed to fully understand and effectively address the issue.

5. How do scientists study the contribution of jet sound to shock waves near supersonic planes?

Scientists use various methods to study the contribution of jet sound to shock waves near supersonic planes. One approach is to conduct wind tunnel tests, where a scaled-down model of the plane is placed in a controlled environment to simulate the conditions of flight. This allows researchers to measure the intensity and characteristics of jet sound and shock waves. Another method is to use computer simulations and mathematical models to predict and analyze the effects of different variables on jet sound and shock waves. Field experiments and measurements from actual supersonic flights are also used to gather data and validate the findings of other methods.

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