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When solving problems of converging diverging nozzles, a shock wave is formed in the flow. For the purpose of problem solving we consider it to be stationary in one point of the flow.

Is this actually physical? Do normal shock waves stay stationary inside the converging diverging nozzle? I thought that normal shock waves move faster than the speed of sound.

Any ideas welcome.

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    $\begingroup$ " I thought that normal shock waves move faster than the speed of sound." - Shock waves move at supersonic speeds relative to the material that they are propagating in. If that material (say some fluid from a nozzle) is moving at high speed compared to the laboratory frame then, yes, the shock wave could appear to be stationary in the laboratory frame. $\endgroup$
    – user93237
    Commented Feb 17, 2018 at 18:49
  • $\begingroup$ OK. That does make sense. However in converging diverging nozzles all the problems I have come across seem to have stationary normal shock waves. Is this a general characteristic for their formation in converging diverging nozzles ? $\endgroup$
    – john melon
    Commented Feb 17, 2018 at 19:48
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    $\begingroup$ To repeat a critical part of @SamuelWeir's comment, those shocks are stationary with respect to the solid hardware, but not with respect to the fluid medium. $\endgroup$ Commented Feb 17, 2018 at 20:53
  • $\begingroup$ I understand this. However, in a converging diverging nozzle, will the flow always be in such a way as to annul the velocity of the shock wave, making it seem stationary to an observatory in the laboratory frame of reference ? $\endgroup$
    – john melon
    Commented Feb 18, 2018 at 16:54
  • $\begingroup$ Related: physics.stackexchange.com/q/134753/59023 $\endgroup$ Commented Feb 19, 2018 at 2:51

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