Supersonic motion: no backward propagating shock waves

In summary, the speaker previously believed that a body accelerating beyond the speed of sound emits a shock wave that propagates spherically backward in the rear hemisphere. However, after reviewing literature on fluid dynamics, they now realize that this is not the case and that every point of a supersonic body generates sonic pressure waves, which only interfere and form shock waves in certain directions. They are unsure why they previously thought pressure waves were always shock waves in supersonic motion, but are grateful to have corrected this misconception. This discussion is a continuation of a previous thread on this topic.
  • #1
voko
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There was a recent thread (now closed) where I claimed that a body accelerating beyond the speed of sound emits a shock wave that propagates spherically backward in the rear hemisphere.

I have reviewed literature on fluid dynamics and it is quite clear to me now that I was wrong. There is no backward-propagating shock waves, spherical or otherwise.

It might perhaps be interesting for the participants of the discussion why I had that idea. In fact, in one message I revealed my underlying reasoning, even though I did not expand on that. My chief mistake was in thinking that every point of a supersonic body excites shock waves, which then propagate spherically in all directions. That is not correct. Every point of a body moving in a fluid, super- and subsonically alike generates sonic pressure waves; in some directions, in supersonic motion, these sonic pressure waves interfere and form shock waves, not everywhere and certainly not in the rear.

It is not clear why I thought that pressure waves were always shock waves in supersonic motion. That seems very strange to me in retrospect. Either way I am happy that I have got rid of that misconception and I thank everyone who participated in the thread.
 
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  • #2
Glad to hear that voko. Maybe the mods can merge this thread into the old closed one.
 
  • #3
Thread closed temporarily for Moderation...

Thread re-opened. This is an allowed continutaion of the previous (now locked) thread.
 
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Related to Supersonic motion: no backward propagating shock waves

1. What is supersonic motion?

Supersonic motion is the movement of an object or fluid at a speed that exceeds the speed of sound in the medium it is traveling through.

2. What are backward propagating shock waves?

Backward propagating shock waves are shock waves that travel in the opposite direction of the supersonic motion. They occur when the object or fluid decelerates from supersonic speed to subsonic speed.

3. Why are backward propagating shock waves a concern in supersonic motion?

Backward propagating shock waves can cause significant damage to the object or fluid, as well as create loud noise and vibrations. They can also disrupt the flow of air or fluid around the object, affecting its performance and stability.

4. How can backward propagating shock waves be avoided in supersonic motion?

To avoid backward propagating shock waves, it is important to design the object or fluid in a way that minimizes the change in speed and direction. This can be achieved through careful aerodynamic shaping and use of control surfaces.

5. What are some practical applications of supersonic motion with no backward propagating shock waves?

Supersonic motion with no backward propagating shock waves has many practical applications, such as in high-speed aircraft and missiles, supersonic wind tunnels, and high-speed trains. It can also be used in medical technology, such as shock wave lithotripsy for breaking up kidney stones.

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