What happens when a plane slows down from hypersonic speed?

[Mustafa Bayram]

Is it results in a new shockwave or does the shockwave continuously created by hypersonic flight suddenly disappear? I guess slowing down from hypersonic speed will cause a lot of vibration on the plane.

 

[Lnewqban]

Welcome, @Mustafa Bayram !

I don't know for sure, but it seems to me that slowing down should be a more peaceful transition, which nature is passing from a high-demand-energy condition (compressing-heating surrounding atmospheric air) to a condition that requires a lot less energy (non-compressed cooler air).

Copied from
https://www.grc.nasa.gov/www/k-12/airplane/mach.html

"There is no upstream influence in a supersonic flow; disturbances are only transmitted downstream."

 

[hutchphd]

slowing down from hypersonic speed

"Hypersonic" is usually defined as above Mach 5. "Supersonic" is defined as above Mach 1. Is that what you mean?

 

[Baluncore]

Is it results in a new shockwave or does the shockwave continuously created by hypersonic flight suddenly disappear?

At, or above, the speed of sound, shockwaves radiate energy from the aircraft.
Below the speed of sound, a shockwave is not generated.

The problem with accelerating through the speed of sound is changes in vehicle stability, and the generation of sufficient thrust.
Decelerating through the speed of sound, changes vehicle stability and wastes energy.

 

[boneh3ad]

I don't really understand the question. There will always be a shock of some kind at the leading edge/tip of a vehicle if $M>1$, and that shock will smoothly change in character as a vehicle accelerates or decelerates through various Mach numbers unless conditions are near the shock detachment point. In that situation you might get abrupt changes between attached oblique shocks and bow shocks.

 

[Mustafa Bayram]

"Hypersonic" is usually defined as above Mach 5. "Supersonic" is defined as above Mach 1. Is that what you mean?

didn't know that thanks, I mean supersonic

 

[Mustafa Bayram]

I don't really understand the question. There will always be a shock of some kind at the leading edge/tip of a vehicle if $M>1$, and that shock will smoothly change in character as a vehicle accelerates or decelerates through various Mach numbers unless conditions are near the shock detachment point. In that situation you might get abrupt changes between attached oblique shocks and bow shocks.

one of my students asks if a second shockwave is created when a plane slows down from a supersonic flight. I think this can be a good answer; a continuous shock wave created at equal or above the speed of sound. when it slows down from the speed of sound vibrations downgrade and the shockwave is disappear.

 

[boneh3ad]

one of my students asks if a second shockwave is created when a plane slows down from a supersonic flight. I think this can be a good answer; a continuous shock wave created at equal or above the speed of sound. when it slows down from the speed of sound vibrations downgrade and the shockwave is disappear.

But that's not what I said. I'm not sure what you mean by "vibrations downgrade." I didn't even mention vibration.

 

[russ_watters]

one of my students asks if a second shockwave is created when a plane slows down from a supersonic flight. I think this can be a good answer; a continuous shock wave created at equal or above the speed of sound.

Yes, I think there is a common misconception around that the boom you hear is the plane breaking the sound barrier - as if there's no boom for an already supersonic plane. That isn't correct; the boom is just the continuously created shock wave passing you as it sweeps across the ground/sky.

 

[sophiecentaur]

Copied from
https://www.grc.nasa.gov/www/k-12/airplane/mach.html

"There is no upstream influence in a supersonic flow; disturbances are only transmitted downstream."

So, I take that to mean that one observer will hear a bang but the next guy along the road will not but no one will hear the bang 'stopping' lol. Makes sense, though; a set of recordings made along the path of the aircraft will have a range of different bangs - the last ones would be a 'quieter bang' perhaps.

 

[DaveC426913]

I might be easier to visualize what happens (at least for me) if one realizes that the only reason that a plane slows down at all is due to the drag caused by that onrushing air. The engines power down and the force on the leading edges of the craft cause the craft to slow, allowing the shockwave to advance, smoothing out the gradient.

 

[sophiecentaur]

I might be easier to visualize what happens (at least for me) if one realizes that the only reason that a plane slows down at all is due to the drag caused by that onrushing air. The engines power down and the force on the leading edges of the craft cause the craft to slow, allowing the shockwave to advance, smoothing out the gradient.

There is only one impulse wave travelling over the ground (or perhaps a double). Before it arrives, you don't hear it. When it passes you, you hear it. When it's gone past you no longer hear it cos it's going away from you.