In turbojet (gas turbine engines), we analyze fluid in terms of pressure. We say that when fluid/air hits stator of compressor, its velocity decreases but static pressure increases due to Bernoulli equation. It assumes that total energy of fluid is conserved.

But why are we assuming this? In my opinion, when fluid hits a surface such as stator(fixed blades), its energy should be down, because it loses energy by hitting something else. It has to automatically transfer some energy to stator.

Instead, we say that its kinetic energy is transformed to static pressure when it hits stator, which is a bit interesting to me. If its velocity decreases naturally in a tube for a normal flow without external affects, that's understandable. However here, there is another object to hit, and this is not a normal velocity decrease.

How do you explain this?

  • $\begingroup$ See engineering.stackexchange.com/q/54667/10902 $\endgroup$
    – Solar Mike
    Commented Apr 13, 2023 at 8:43
  • $\begingroup$ See Engineering Thermodynamics, Work and Heat Transfer by Rogers & Mayhew $\endgroup$
    – Solar Mike
    Commented Apr 13, 2023 at 8:44
  • $\begingroup$ @SolarMike They are not regarding my current question. Please stop searching my previous posts and pasting their links in my new posts. They are totally different questions. Please let others answer my question. Thanks. $\endgroup$
    – Jawel7
    Commented Apr 13, 2023 at 9:26
  • $\begingroup$ Read the textbook... and question suggestions come from links provided... $\endgroup$
    – Solar Mike
    Commented Apr 13, 2023 at 9:29

1 Answer 1


Bernoulli's principle is proven, and can be proven by anyone (including yourself) experimentally; it is not an "assumption". Generally it is better to experiment and learn to trust the physics on simpler systems before advancing to complex systems like turbines where there is a lot going on.

An ideal gas and the Kinetic theory of gases state that the particles only undergo elastic collisions which means momentum is conserved. Think of them like rubber balls. You can think of a stator blade like wall. When a rubber ball comes and hits the wall, it bounces off with opposite momentum but with 100% of its energy. As more and more of these balls are thrown at the wall they not only bounce off the wall but off of each other. The concentration and speed of balls near the wall surface will increase, resulting in an increase in pressure and temperature in the area near the wall.


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