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The most common explanation to this phenomenon which I have read is that the pressure disturbance signal cannot propagate upstream, as the medium in which it travels itself flows downstream, so signals can no longer reach the upstream part, hence flow is choked.

How I look at is, that there are a lot of particles connected to each other through springs or restoring forces, as one particle is pulled away, it exerts a pulling effect on the other particles and fluid flows. What I think is that, there is some significant time of interaction between two connected particles, during this time impulse is transferred from one particle to another. If flow velocity is too high(greater than velocity at which disturbances propagate), then the particles stop exerting pulling forces too early and the time of interaction is reduced. This lowers the impulse transmitted and the particle can no longer pull the upstream particles with it, as the time of interaction is less than adequate.

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Yes, it does.

Air molecules can be modeled as a very large number of hard little rubber balls that continuously bounce violently off one another. Because they have mass and a certain "springiness", there will be a characteristic velocity at which vibrations or other disturbances can be propagated between them, and travel over long distances. This is the velocity of sound in air.

When the flow velocity of air or any gas through a constriction in a pipe approaches the velocity of sound in that gas, then the gas molecules approaching the constriction cannot smoothly adjust to the presence of the constriction ahead of them before they physically slam into it. A shock wave forms in the constriction, against which the gas molecules pile up, and flow in the constriction is said to be choked.

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  • $\begingroup$ Yes, this makes sense. There is a characteristic time interval for which the particles should interact in order to propagate disrturbances in the medium, if the time of interaction is reduced, the signal or impulse is not effectively transmitted to the connecting particles, so as to cause flow. The change will be too sudden to affect other particles in layman terms. $\endgroup$
    – user141356
    Commented Jun 8, 2020 at 20:10
  • $\begingroup$ Does my explanation about impulse transmission, between two such balls connected by springy forces hold? I am trying to arrive at the same conclusion, through a different perspective. Please guide me!! $\endgroup$
    – user141356
    Commented Jun 8, 2020 at 21:47
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    $\begingroup$ yes you are on the right track, but you must accommodate the presence of a very large number of balls and springs- also note the springs are not linked firmly to each other; it is better to think of the gas molecules as rubber balls that are far apart from one another most of the time. $\endgroup$
    – niels nielsen
    Commented Jun 9, 2020 at 0:06
  • $\begingroup$ Yes, I will keep these finer details in mind. But the bigger picture of some finite time of interaction between two particles, so as to transfer significant impulse and pull each other together for flow to occur, remains intact, right? This explanation came intuitively to me, once I pictured things at particle level. Thank you for your patience and help. Very grateful. $\endgroup$
    – user141356
    Commented Jun 9, 2020 at 1:05
  • $\begingroup$ I’ve just stumbled across this, and I’ve been trying to figure this out for days now. In choked flow, why can’t it accelerate past sonic speed? If the choked flow is in a pipe, and the end of the pipe has a low pressure section, what is preventing the upstream molecules from accelerating and filling this low pressure gap? No molecule communication has to be done; all that happens is that the upstream molecules feel the missing downstream molecules beside them, so it should accelerate? $\endgroup$
    – Wyatt
    Commented Nov 15 at 5:40

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