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As I understand it, in rocket propulsion a converging/diverging nozzle is used to convert the random velocity vectors of the combustion chamber gases into a mostly unidirectional velocity field at the exhaust nozzle. What are the physics of this process?

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closed as too broad by Kyle Kanos, ACuriousMind, Sofia, John Rennie, tom Mar 14 '15 at 20:17

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ This seems to be a fairly broad question. $\endgroup$ – Kyle Kanos Mar 13 '15 at 20:28
  • $\begingroup$ I'm voting to close this question as off-topic because the question belongs to the aviation site $\endgroup$ – Sofia Mar 13 '15 at 22:54
  • $\begingroup$ maybe you could read en.wikipedia.org/wiki/Rocket_engine_nozzle, study it carefully because there are lot of concepts covered in it and then ask specific (physics based) questions based on the parts of the article you need clarified? $\endgroup$ – user74893 Mar 13 '15 at 23:05
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In a rocket, propulsion occurs when the combustion products are expelled in a direction opposite to the direction of intended thrust. Sending it sideways does not move you in the right direction - so it's important to have a coherent output.

You would also like the velocity of the exhaust gas to be as high as possible. It turns out that if your exhaust gas velocity is supersonic, then the shaped nozzle will cause further acceleration of the gas - in the process producing more thrust.

This is nicely explained on this NASA website from which I copy the following for ease of reference - but I recommend you read the original (which includes a detailed description):

enter image description here

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