Fluid Mechanics Help: Sonic Pressure Wave Behavior in Pipes

In summary: Thanks!If two tennis balls collide, kinetic energy will always be lost, but momentum will always be conserved.
  • #1
Rotormaster
6
0
Hi guys.

I have a question on sonic pressure wave behavior in pipes.

When a pressure wave traversing down a pipe encounters a change in cross-section, namely, a convergence say like that of an expansion chamber, a negative pressure wave is reflected back in the opposite direction. My question is, does the energy of the reflected negative pressure wave proportionally equal the energy that the original wave loses in encountering the convergence?
 
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  • #2
Hi Rotormaster! :smile:
Rotormaster said:
… does the energy of the reflected negative pressure wave proportionally equal the energy that the original wave loses in encountering the convergence?

No.

If we treat this as a collision, then of course https://www.physicsforums.com/library.php?do=view_item&itemid=53" of a musical instrument), so we need one extra constraint …

that constraint is the fixed speed of the waves, not their energy. :wink:
 
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  • #3
tiny-tim said:
Hi Rotormaster! :smile:


No.

If we treat this as a collision, then of course https://www.physicsforums.com/library.php?do=view_item&itemid=53" of a musical instrument), so we need one extra constraint …

that constraint is the fixed speed of the waves, not their energy. :wink:

Hi there!

I find this interesting but I don't quite understand what you said.

Obviously, momentum is conserved. And of course, their speed is fixed as we are talking about sonic waves. And, clearly, their energy is obviously not fixed as they are ever engaging in contact with their environment, until they dissipate that is.

But why did you say that the momentum lost by the original wave is equal to the momentum of the reflected wave??

Can you elaborate?

Thanks.
 
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  • #4
Welcome to PF!

Hi Juval! Welcome to PF! :wink:
Juval said:
But why did you say that the momentum lost by the original wave is equal to the momentum of the reflected wave??

?? :confused:

As you said …
Obviously, momentum is conserved.

… and if momentum is conserved, where else can the "lost" momentum go? :smile:​
 
  • #5


tiny-tim said:
Hi Juval! Welcome to PF! :wink:


?? :confused:

As you said …


… and if momentum is conserved, where else can the "lost" momentum go? :smile:​

Thanks!

Yes, I see what you are saying with that, but that is not what I was referring to.

What I meant was that, a question was asked in the initial post whether the energy of the reflected wave directly equals the energy lost by the original wave. You answered this with a "no"... But then you went on to say that "the momentum lost by the original wave is equal to the reflected wave"??

Hopefully you can explain what you meant by that.

Sorry, I should have made myself clearer from the beginning. :)
 
  • #6
Hi Juval! :smile:

If two tennis balls collide, kinetic energy will always be lost, but momentum will always be conserved.

The momentum lost by one tennis ball will always equal the momentum gained by the other tennis ball.

It's the same with a sound wave …

kinetic energy will be lost (and disappear into other forms of energy)

but the momentum lost by the original wave will equal the momentum gained by the reflected wave.​
 

Related to Fluid Mechanics Help: Sonic Pressure Wave Behavior in Pipes

1. What is a sonic pressure wave in pipes and how does it behave?

A sonic pressure wave is a type of wave that travels through a fluid, such as water or air, at the speed of sound. In pipes, these waves are generated by sudden changes in the fluid flow, such as a valve opening or closing. They behave by creating high and low pressure areas in the fluid, which can cause vibrations and potentially damage the pipe if not properly controlled.

2. How can sonic pressure waves in pipes be measured?

There are several methods for measuring sonic pressure waves in pipes, including using pressure transducers or sensors placed at various points along the pipe. These devices can measure the pressure fluctuations caused by the waves and provide data for analysis and control of the fluid flow.

3. What factors affect the behavior of sonic pressure waves in pipes?

The behavior of sonic pressure waves in pipes can be influenced by various factors, such as the fluid velocity, pipe diameter, and temperature. Changes in these factors can alter the speed of the waves and their strength, which can impact the overall behavior in the pipe system.

4. How can sonic pressure waves in pipes be controlled?

To control sonic pressure waves in pipes, it is important to design the pipe system with proper dimensions and fluid flow rates, as well as utilizing devices such as dampeners or surge tanks to absorb and dissipate the waves. Additionally, proper valve and pump operation can also help to mitigate the effects of sonic pressure waves.

5. What are the potential risks associated with sonic pressure waves in pipes?

Sonic pressure waves in pipes can pose risks to the integrity of the pipe system, as well as potential safety hazards for workers and the surrounding environment. If not properly controlled, these waves can cause pipe failures, leaks, and other damage. They can also create high levels of noise and vibration, which can be harmful to workers and nearby structures.

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