How does a jet-engine compressor compress air?

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Discussion Overview

The discussion centers on the mechanics of how a jet-engine compressor compresses air, exploring the stages of compression, the role of rotating vanes, and the interaction between the compressor and turbine sections. Participants delve into theoretical and practical aspects of jet engine design, including the principles of airflow and pressure changes within the engine.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • Some participants describe the compressor as having various stages of rotating vanes that incrementally compress air, with a diffuser at the end that further increases static pressure.
  • Others explain that the rotating blades impart momentum and energy to the air, pushing it downstream, and highlight the role of the turbine in converting energy from heated gases.
  • One participant emphasizes that the thrust of the engine is produced via Newton's 3rd law due to the acceleration of the air stream, rather than by the turbines themselves.
  • Another participant mentions that gas turbine compressors primarily accelerate air, with pressure rise occurring when the air enters the larger combustion section, referencing Bernoulli's principle.
  • Some participants discuss the use of centrifugal compressors in conjunction with axial compressors, noting that centrifugal stages are more common in smaller engines and have different efficiency characteristics.
  • There is a mention of confusion regarding the role of turbines in thrust generation, with some clarifying that turbines do not create thrust but are necessary for driving the compressor.
  • Participants also discuss the efficiency of different engine designs, noting that larger engines may be more efficient with slower-moving fuel-air mixtures compared to smaller engines.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement on various points, particularly regarding the mechanics of thrust generation and the efficiency of different compressor types. Some views remain contested, particularly around the roles of the compressor and turbine in thrust production and the specifics of compressor design.

Contextual Notes

There are unresolved questions regarding the efficiency of different compressor types and the specific mechanics of how centrifugal compressors integrate with axial designs. Some assumptions about airflow and pressure changes may depend on definitions not fully explored in the discussion.

Who May Find This Useful

This discussion may be useful for individuals interested in aerospace engineering, jet propulsion, and the technical workings of gas turbine engines.

  • #31
That's squarely in Fred's arena, but I don't think so. There are a lot of variables that contribute to creating thrust, such as type of fuel, combustion temperature, nozzle design, exhaust temperature...
 
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  • #32
Theoretically, the most basic equation for thrust is

F_t= \dot{m}(V_{OUT}-V_{IN})

where
\dot{m} = air mass flow rate
V_{OUT} = air exit velocity
V_{IN} = air inlet velocity
 
  • #33
1.ooohhhh i thought thrust= exhaust velocity * rate of combustion
is this wrong?

2.which part of the aircraft experiences this reaction force(thrust) first? (is this question stupid?)
3.is there a difference between thrust and propulsion?
4.and for compression?
there's no theoretical equation for compression?
 
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