About difference in Velocity and motion in Jet engines

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Discussion Overview

The discussion revolves around the mechanics of jet engines, specifically focusing on the differences in velocity and motion generated by the compression of air and the combustion process. Participants explore the roles of various components in jet propulsion, including air compression, combustion, and exhaust dynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the process of compressing air at high speed and its relation to motion, noting a perceived difference in velocity that propels the engine forward.
  • Another participant questions the omission of the combustion process in the initial explanation, suggesting it is a critical component of jet propulsion.
  • Some participants argue that combustion alone does not provide motion, while others assert that it plays a significant role in the operation of jet engines.
  • A participant highlights the importance of exhaust in the overall functioning of jet engines, implying it contributes to thrust generation.
  • One participant proposes a hypothetical scenario involving gas volume changes to illustrate the relationship between incoming and outgoing velocities in jet engines.

Areas of Agreement / Disagreement

Participants express differing views on the role of combustion in generating motion, with some asserting its importance while others question its necessity. The discussion remains unresolved regarding the precise contributions of each component to jet engine operation.

Contextual Notes

There are missing assumptions regarding the definitions of motion and velocity in the context of jet engines, as well as unresolved mathematical relationships related to gas volumes and velocities.

ZdMh
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I was watching a video about jet engines, and it was obvious for me and for the instructor that if we compress air at high speed from the gas turbine inlet, then after multiple stages collide with the turbines blades inside, the body will move in the sense of difference in velocity, so forward. At a moment it was obvious, but I can't really explain it why? Can you help me with that using some formulas.
 
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It sounds like you are leaving the combustion part out of your description...?
 
berkeman said:
It sounds like you are leaving the combustion part out of your description...?

But the combustion itself can't necessarily provide a motion
 
Don't forget the exhaust...
 
ZdMh said:
... the body will move in the sense of difference in velocity, so forward.
ZdMh said:
But the combustion itself can't necessarily provide a motion

Could you explain these parts a little better, please?
 
ZdMh said:
But the combustion itself can't necessarily provide a motion
Maybe not necessarily, but in a jet engine it sure as heck does! :smile:

1619099906470.png

https://en.wikipedia.org/wiki/Components_of_jet_engines
 
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The combustion heats the gas causing the volume to increase.

Choosing an arbitrary number, suppose we have
one cubic meter per second coming in and 100 m³/s going out. What does that tell you about the velocities?
 
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