About difference in Velocity and motion in Jet engines

[ZdMh]

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.

 

[berkeman]

It sounds like you are leaving the combustion part out of your description...?

 

[ZdMh]

It sounds like you are leaving the combustion part out of your description...?

But the combustion itself can't necessarily provide a motion

 

[onatirec]

Don't forget the exhaust...

 

[Lnewqban]

... the body will move in the sense of difference in velocity, so forward.

But the combustion itself can't necessarily provide a motion

Could you explain these parts a little better, please?

 

[berkeman]

But the combustion itself can't necessarily provide a motion

Maybe not necessarily, but in a jet engine it sure as heck does!

https://en.wikipedia.org/wiki/Components_of_jet_engines

 

[anorlunda]

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?